Added ECHO cmd and fixed some timing issues

docs/ARCHITECTURE.md

@@ -205,7 +205,7 @@ sequenceDiagram
 ```
 
 **Beispiel-Implementierung:** `main/cmd/cmd_accel_deadzone.c`  
-**Weitere Bridge-Handler:** `cmd_accel_stream.c`, `cmd_tap_notify.c`, `cmd_led_ring.c`, `cmd_espnow_find_me.c`, `cmd_restart.c`, `cmd_espnow_unicast_test.c`, `cmd/cmd_ota.c` (OTA + `ota_espnow.c`).
+**Weitere Bridge-Handler:** `cmd_accel_stream.c`, `cmd_tap_notify.c`, `cmd_led_ring.c`, `cmd_espnow_find_me.c`, `cmd_restart.c`, `cmd_espnow_unicast_test.c`, `cmd_espnow_echo_ping.c`, `cmd/cmd_ota.c` (OTA + `ota_espnow.c`).
 
 **Nur Master / nur Cache (kein Slave-Roundtrip):** `cmd_client_info.c`, `cmd_battery.c`, `cmd_cache_status.c`, `cmd_version.c`.
 

docs/DOCUMENTATION.md

@@ -181,6 +181,8 @@ UART_CMD_REQ(&uart_msg, alox_UartMessage_accel_deadzone_request_tag, accel_deadz
 | `ESPNOW_FIND_ME` | M→S | `find_me` | LED-Locate |
 | `ESPNOW_RESTART` | M→S | `restart` | Reboot Slave |
 | `ESPNOW_UNICAST_TEST` | M→S | `unicast_test` | Link-Test |
+| `ESPNOW_ECHO_PING` | M→S | `echo_ping` | Latenztest (Host-Timestamp + `master_time_us`) |
+| `ESPNOW_ECHO_PONG` | S→M | `echo_pong` | Echo unverändert zurück zum Master |
 | `ESPNOW_OTA_*` | M↔S | `ota_*` | Firmware-Verteilung |
 
 ### 6.3 Zeitkonstanten (`esp_now_comm.c`)
@@ -193,6 +195,7 @@ UART_CMD_REQ(&uart_msg, alox_UartMessage_accel_deadzone_request_tag, accel_deadz
 | Master-Verlust (Slave) | 5 s ohne Discover |
 | Accel-Stream | 16 ms |
 | Batterie-Report | 30 s (+ einmal 150 ms nach Join) |
+| Echo-Ping Timeout (Master) | 500 ms (`ESPNOW_ECHO_PING_TIMEOUT_MS`) |
 
 ### 6.4 `EspNowSlavePresence`
 
@@ -229,6 +232,7 @@ Nur auf dem **Master** registriert (`powerpod.c`). IDs aus `MessageType` in `uar
 | 26 | BATTERY_STATUS | `cmd_battery.c` | Cache LiPo Master + Slaves |
 | 27 | TAP_NOTIFY | `cmd_tap_notify.c` | Tap-Weiterleitung konfigurieren |
 | 29 | CACHE_STATUS | `cmd_cache_status.c` | Accel + Tap Cache (ein Round-Trip) |
+| 30 | ESPNOW_ECHO_PING | `cmd_espnow_echo_ping.c` | Timestamp-Echo über ESP-NOW (Latenztest) |
 
 ### 7.1 VERSION (3)
 
@@ -287,6 +291,31 @@ Nur auf dem **Master** registriert (`powerpod.c`). IDs aus `MessageType` in `uar
 
 Minimaler Master→Slave-Ping; Slave loggt `UNICAST TEST OK`.
 
+### 7.11 ESPNOW_ECHO_PING (30)
+
+Round-Trip-Latenztest zu einem **Slave** (`client_id` > 0, muss in der Registry sein).
+
+**Ablauf:**
+
+1. Host (goTool) setzt `timestamp_us` (Unix-µs) und sendet `EspNowEchoPingRequest` per UART.
+2. Master (`cmd_espnow_echo_ping.c`) löst MAC aus Registry auf, ruft `esp_now_comm_echo_ping()` auf.
+3. Master sendet `ESPNOW_ECHO_PING` mit `host_timestamp_us` und `master_time_us` (`esp_timer_get_time()` kurz vor Send).
+4. Slave (`handle_echo_ping`) antwortet mit `ESPNOW_ECHO_PONG` (Felder unverändert).
+5. Master empfängt Pong, berechnet `esp_rtt_us = esp_timer_get_time() - master_time_us`, antwortet per UART.
+
+**Request:** `client_id`, `timestamp_us` (vom Host gesetzt).
+
+**Response:** `success`, `client_id`, `timestamp_us` (echoed), `esp_rtt_us` (nur bei Erfolg).
+
+| Feld | Quelle | Bedeutung |
+|------|--------|-----------|
+| `timestamp_us` | Host → Slave → Host | Korrelations-ID; muss mit Request übereinstimmen |
+| `esp_rtt_us` | Master | Rohe µs-Differenz von `esp_timer_get_time()` (Ping-Send → Pong-Empfang im `recv_cb`) |
+
+**Implementierung:** `main/cmd/cmd_espnow_echo_ping.c`, `esp_now_comm_echo_ping()` in `esp_now_master.c`, Slave `handle_echo_ping` in `esp_now_slave.c`.
+
+**Host-seitig (goTool):** `rtt_ms` = volle UART-Kette (Send bis Response-Empfang); unabhängig von `esp_rtt_us`.
+
 ---
 
 ## 8. OTA
@@ -427,6 +456,7 @@ Includes in generierten `.pb.c` müssen `"uart_messages.pb.h"` heißen (nicht `m
 | `cmd_espnow_find_me.c` | FIND_ME |
 | `cmd_restart.c` | RESTART |
 | `cmd_espnow_unicast_test.c` | ESPNOW_UNICAST_TEST |
+| `cmd_espnow_echo_ping.c` | ESPNOW_ECHO_PING |
 | `cmd_ota.c` | OTA_* |
 | `cmd_ota_slave_progress.c` | OTA_SLAVE_PROGRESS |
 

goTool/README.md

@@ -28,6 +28,7 @@ go run . -port /dev/ttyUSB0 clients
 | `tap-notify` | `0x1b` | Get/set which tap kinds (single/double/triple) notify via ESP-NOW (`-set`, `-client`, `-all`, `-single`, `-double`, `-triple`) |
 | `cache-status` | `0x1d` | Subscribed accel + tap cache (`CACHE_STATUS`); one UART round-trip for 16 ms polling |
 | `unicast-test` | `0x07` | Sends ESP-NOW unicast test to one slave (`-client`, `-seq`) |
+| `echo-ping` | `0x1e` | ESP-NOW echo round-trip to one slave (`-client`); prints `rtt_ms` (host UART chain) and `esp_rtt_us` (master ESP-NOW, raw µs) |
 | `test` | — | Run an automated scenario (JSON configs under `testdata/`) |
 | `serve` | — | Web dashboard at `http://localhost:8080` (WebSocket live updates) |
 | `ota` | 16–19 | UART firmware upload to master; firmware then pushes to slaves via ESP-NOW |
@@ -113,8 +114,20 @@ go run . -port /dev/ttyUSB0 unicast-test -client 16 -seq 42
 
 On success the slave serial log should show `UNICAST TEST OK from master … seq=42`.
 
+```bash
+go run . -port /dev/ttyUSB0 echo-ping -client 16
+```
+
+Measures latency to one slave. `rtt_ms` is the full host round-trip (UART + ESP-NOW + UART back). `esp_rtt_us` is the master-side ESP-NOW leg only (`esp_timer_get_time()` delta, raw microseconds from firmware).
+
 Example output:
 
+```
+echo ping: success=true client_id=16 rtt_ms=49.729 esp_rtt_us=18234
+```
+
+`clients` example:
+
 ```
 clients (2):
   [0] id=42 mac=aabbccddeeff ver=1 available=true used=false last_ping=250 last_success_ping=250

goTool/api_serve.go

@@ -41,6 +41,19 @@ type unicastAPIResponse struct {
 	Error   string `json:"error,omitempty"`
 }
 
+type echoPingAPIRequest struct {
+	ClientID uint32 `json:"client_id"`
+}
+
+type echoPingAPIResponse struct {
+	Success     bool    `json:"success"`
+	ClientID    uint32  `json:"client_id,omitempty"`
+	TimestampUs uint64  `json:"timestamp_us,omitempty"`
+	RttMs       float64 `json:"rtt_ms"`
+	EspRttUs    uint32  `json:"esp_rtt_us"`
+	Error       string  `json:"error,omitempty"`
+}
+
 type findMeAPIRequest struct {
 	ClientID uint32 `json:"client_id"`
 }
@@ -91,6 +104,13 @@ func mountServeAPI(mux *http.ServeMux, link *managedSerial, hub *wsHub, streamCt
 		}
 		serveUnicastTest(w, r, link)
 	})
+	mux.HandleFunc("/api/echo-ping", func(w http.ResponseWriter, r *http.Request) {
+		if r.Method != http.MethodPost {
+			http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
+			return
+		}
+		serveEchoPing(w, r, link)
+	})
 	mux.HandleFunc("/api/find-me", func(w http.ResponseWriter, r *http.Request) {
 		if r.Method != http.MethodPost {
 			http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
@@ -316,6 +336,30 @@ func serveUnicastTest(w http.ResponseWriter, r *http.Request, link *managedSeria
 	})
 }
 
+func serveEchoPing(w http.ResponseWriter, r *http.Request, link *managedSerial) {
+	var body echoPingAPIRequest
+	if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
+		writeJSON(w, http.StatusBadRequest, echoPingAPIResponse{Error: "invalid JSON"})
+		return
+	}
+	if body.ClientID == 0 {
+		writeJSON(w, http.StatusBadRequest, echoPingAPIResponse{Error: "client_id required"})
+		return
+	}
+	result, err := link.EchoPing(body.ClientID)
+	if err != nil {
+		writeJSON(w, http.StatusServiceUnavailable, echoPingAPIResponse{Error: err.Error()})
+		return
+	}
+	writeJSON(w, http.StatusOK, echoPingAPIResponse{
+		Success:     result.Success,
+		ClientID:    result.ClientID,
+		TimestampUs: result.TimestampUs,
+		RttMs:       result.RttMs,
+		EspRttUs:    result.EspRttUs,
+	})
+}
+
 func parseUintQuery(r *http.Request, key string, def uint32) (uint32, error) {
 	s := r.URL.Query().Get(key)
 	if s == "" {

goTool/client_api.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"fmt"
+	"time"
 
 	"google.golang.org/protobuf/proto"
 
@@ -410,6 +411,66 @@ func (s *serialPort) espnowUnicastTest(clientID, seq uint32) (*pb.EspNowUnicastT
 	return r, nil
 }
 
+// EchoPingResult is the host-side round-trip for ESP-NOW echo ping.
+type EchoPingResult struct {
+	Success     bool    `json:"success"`
+	ClientID    uint32  `json:"client_id"`
+	TimestampUs uint64  `json:"timestamp_us"`
+	RttMs       float64 `json:"rtt_ms"`     // goTool: full UART round-trip
+	EspRttUs    uint32  `json:"esp_rtt_us"` // master: µs delta ping send → pong recv
+}
+
+func (s *serialPort) echoPing(clientID uint32) (*EchoPingResult, error) {
+	t0 := time.Now()
+	timestampUs := uint64(t0.UnixMicro())
+	req := &pb.EspNowEchoPingRequest{
+		ClientId:    clientID,
+		TimestampUs: timestampUs,
+	}
+	msg := &pb.UartMessage{
+		Type: pb.MessageType_ESPNOW_ECHO_PING,
+		Payload: &pb.UartMessage_EspnowEchoPingRequest{
+			EspnowEchoPingRequest: req,
+		},
+	}
+	body, err := proto.Marshal(msg)
+	if err != nil {
+		return nil, fmt.Errorf("encode: %w", err)
+	}
+	payload := append([]byte{byte(pb.MessageType_ESPNOW_ECHO_PING)}, body...)
+	respPayload, err := s.exchangePayload(payload, "ESPNOW_ECHO_PING")
+	if err != nil {
+		return nil, err
+	}
+	rttMs := float64(time.Since(t0).Microseconds()) / 1000.0
+
+	var respMsg pb.UartMessage
+	if err := proto.Unmarshal(respPayload[1:], &respMsg); err != nil {
+		return nil, fmt.Errorf("decode: %w", err)
+	}
+	r := respMsg.GetEspnowEchoPingResponse()
+	if r == nil {
+		return nil, fmt.Errorf("missing espnow_echo_ping_response")
+	}
+	if !r.GetSuccess() {
+		return &EchoPingResult{
+			Success:  false,
+			ClientID: r.GetClientId(),
+			RttMs:    rttMs,
+		}, nil
+	}
+	if r.GetTimestampUs() != timestampUs {
+		return nil, fmt.Errorf("timestamp mismatch: sent %d got %d", timestampUs, r.GetTimestampUs())
+	}
+	return &EchoPingResult{
+		Success:     true,
+		ClientID:    r.GetClientId(),
+		TimestampUs: r.GetTimestampUs(),
+		RttMs:       rttMs,
+		EspRttUs:    r.GetEspRttUs(),
+	}, nil
+}
+
 func (m *managedSerial) FindMe(clientID uint32) error {
 	return m.withPort(func(sp *serialPort) error {
 		return runFindMeClient(sp, clientID)
@@ -490,6 +551,20 @@ func (s *serialPort) EspnowUnicastTest(clientID, seq uint32) (*pb.EspNowUnicastT
 	return s.espnowUnicastTest(clientID, seq)
 }
 
+func (s *serialPort) EchoPing(clientID uint32) (*EchoPingResult, error) {
+	return s.echoPing(clientID)
+}
+
+func (m *managedSerial) EchoPing(clientID uint32) (*EchoPingResult, error) {
+	var result *EchoPingResult
+	err := m.withPort(func(sp *serialPort) error {
+		var e error
+		result, e = sp.echoPing(clientID)
+		return e
+	})
+	return result, err
+}
+
 func (s *serialPort) LedRing(req *pb.LedRingProgressRequest) (*pb.LedRingProgressResponse, error) {
 	return s.ledRingProgress(req)
 }

goTool/cmd_echo_ping.go

@@ -0,0 +1,26 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+)
+
+func runEchoPing(sp *serialPort, args []string) error {
+	fs := flag.NewFlagSet("echo-ping", flag.ExitOnError)
+	clientID := fs.Uint("client", 0, "slave client id from `clients`")
+	if err := fs.Parse(args); err != nil {
+		return err
+	}
+	if *clientID == 0 {
+		return fmt.Errorf("client id required (see `gotool clients`)")
+	}
+
+	r, err := sp.echoPing(uint32(*clientID))
+	if err != nil {
+		return err
+	}
+
+	fmt.Printf("echo ping: success=%v client_id=%d rtt_ms=%.3f esp_rtt_us=%d\n",
+		r.Success, r.ClientID, r.RttMs, r.EspRttUs)
+	return nil
+}

goTool/docs/API_REST.md

@@ -216,6 +216,54 @@ Content-Type: application/json
 {"client_id": 16, "seq": 42}
 ```
 
+### Echo ping (ESP-NOW round-trip latency)
+
+```http
+POST /api/echo-ping
+Content-Type: application/json
+{"client_id": 16}
+```
+
+`client_id` must be a registered slave id (`> 0`). The host sends a microsecond timestamp; the master forwards it over ESP-NOW and the slave echoes it back unchanged.
+
+**Flow:** Host → UART → `cmd_espnow_echo_ping` → `ESPNOW_ECHO_PING` (with `master_time_us` from `esp_timer_get_time()`) → Slave → `ESPNOW_ECHO_PONG` → Master `recv_cb` → UART response.
+
+**Response fields:**
+
+| Field | Unit | Meaning |
+|-------|------|---------|
+| `success` | — | `true` if pong received within 500 ms |
+| `client_id` | — | Echo of request |
+| `timestamp_us` | µs (Unix) | Echoed host timestamp; must match request on success |
+| `rtt_ms` | ms | **Host-side** round-trip: goTool send → UART response (full chain incl. USB serial) |
+| `esp_rtt_us` | µs | **Master-side** ESP-NOW only: `esp_timer_get_time()` delta from ping send to pong recv |
+
+`esp_rtt_us` is the raw firmware value (microseconds, not converted). The web dashboard displays it converted to milliseconds for readability (`esp_rtt_us / 1000`, 3 decimal places). The success banner stays visible for at least 5 seconds.
+
+```json
+{
+  "success": true,
+  "client_id": 16,
+  "timestamp_us": 1717654321123456,
+  "rtt_ms": 49.729,
+  "esp_rtt_us": 18234
+}
+```
+
+On failure (`success: false`), `esp_rtt_us` is omitted; `rtt_ms` still reflects the host round-trip. HTTP 503 if UART exchange fails (e.g. timeout, client not in registry).
+
+**CLI:**
+
+```bash
+go run . -port /dev/ttyUSB0 echo-ping -client 16
+```
+
+Example output:
+
+```
+echo ping: success=true client_id=16 rtt_ms=49.729 esp_rtt_us=18234
+```
+
 ### Find me
 
 ```http
@@ -280,5 +328,6 @@ Same as external API:
 | Einzelner Slave | `client_id: <id>` |
 | Alle Slaves deadzone | `all_clients` + `slaves_only` on POST |
 | Unicast test | `POST /api/unicast-test` |
+| Echo ping | `POST /api/echo-ping` (per-slave latency; UI shows Host ms + ESP ms) |
 | Tap notify S/D/T | `PUT /api/clients/{id}/tap-notify` |
 | Tap receive (UI) | Live stream + tap notify; see WebSocket doc for external API |

goTool/docs/API_WEBSOCKET.md

@@ -5,6 +5,7 @@ External API: `ws://localhost:8081/ws` (default `-api-addr`, disable with empty
 Start with `go run . -port /dev/ttyUSB0 serve`.
 
 ---
+
 ## Connection flow
 
 1. Connect → server sends `hello` (push off; defaults and command list).
@@ -19,20 +20,24 @@ On disconnect, `set_stream` state for that socket is dropped. Firmware settings
 
 ## Two layers (firmware vs host)
 
+
 | Layer              | Commands                             | Effect                                                             |
-|-------|----------|--------|
+| ------------------ | ------------------------------------ | ------------------------------------------------------------------ |
 | Firmware (ESP-NOW) | `set_input_stream`, `set_tap_notify` | Per `client_id`: slave sends accel and/or tap events to the master |
 | This connection    | `set_stream`                         | Whether you receive push JSON on this socket                       |
 
+
 UART polling runs only when at least one connection has `receive_input: true` **and** at least one slave streams input or has tap notify enabled. `set_tap_notify` alone does not enable push — you still need `set_stream`.
 
 ### Push timing (per connection)
 
+
 | Field         | Where                                  | Meaning                                                      |
-|-------|-------|---------|
+| ------------- | -------------------------------------- | ------------------------------------------------------------ |
 | `interval_ms` | `hello`, `set_stream`, `stream_status` | Minimum ms between `input` pushes on this socket (1 … 10000) |
 | `pre_fetch`   | `set_stream`, `stream_status`          | Ms before each push when the host starts the UART cache read |
 
+
 Global UART poll interval = minimum `interval_ms` among all connections with push enabled.
 
 Typical sequence:
@@ -74,8 +79,9 @@ Combines latest accel cache and visible tap state for every slave slot on the ma
 }
 ```
 
+
 | Field          | Meaning                                                              |
-|-------|---------|
+| -------------- | -------------------------------------------------------------------- |
 | `t`            | Unix timestamp in nanoseconds when the host read the cache           |
 | `success`      | `true` if `CACHE_STATUS` succeeded                                   |
 | `clients[]`    | One entry per slave slot (includes invalid/stale entries)            |
@@ -86,6 +92,7 @@ Combines latest accel cache and visible tap state for every slave slot on the ma
 | `tap_kind`     | `"single"`, `"double"`, or `"triple"`; omit when no recent tap       |
 | `tap_age_ms`   | Ms since tap in master cache; omit with `tap_kind`                   |
 
+
 Tap events stay visible for `tap_display_min_ms` (2000, in `hello`) after the API first saw them.
 
 **Failure** (no `clients` array):
@@ -198,8 +205,9 @@ Response `tap_notify_status`:
 {"type":"set_led_ring","mode":"find-me","all_clients":true,"slaves_only":true}
 ```
 
+
 | Request `mode` | Notes                       |
-|----------------|--------|
+| -------------- | --------------------------- |
 | `clear`        | Turn off                    |
 | `color`        | Full ring RGB + `intensity` |
 | `progress`     | `progress` 0–100            |
@@ -207,6 +215,7 @@ Response `tap_notify_status`:
 | `blink`        | `blink_ms`, `blink_count`   |
 | `find-me`      | Locate pod                  |
 
+
 Target: `client_id` (`0` = master) or `all_clients` (+ optional `slaves_only`).
 
 Response `led_ring_status` — `mode` is numeric: 0=clear, 1=progress, 2=digit, 3=blink, 4=find-me, 5=color.
@@ -240,3 +249,4 @@ Response `battery_status`:
   ]
 }
 ```
+

goTool/main.go

@@ -19,6 +19,7 @@ func usage() {
 	fmt.Fprintf(os.Stderr, "  tap-notify    get/set which tap kinds notify via ESP-NOW\n")
 	fmt.Fprintf(os.Stderr, "  cache-status  subscribed accel + tap cache (one UART round-trip)\n")
 	fmt.Fprintf(os.Stderr, "  unicast-test  send ESP-NOW unicast test to one slave\n")
+	fmt.Fprintf(os.Stderr, "  echo-ping     ESP-NOW timestamp echo round-trip to one slave\n")
 	fmt.Fprintf(os.Stderr, "  test          run automated scenario (see testdata/)\n")
 	fmt.Fprintf(os.Stderr, "  serve         web dashboard (Bootstrap + WebSocket)\n")
 	fmt.Fprintf(os.Stderr, "  ota           UART OTA upload (A/B partitions)\n")
@@ -52,7 +53,7 @@ func main() {
 			os.Exit(2)
 		}
 		runErr = runServe(*portName, *baud, flag.Args()[1:])
-	case "version", "clients", "client-info", "deadzone", "accel-deadzone", "tap-notify", "tap_notify", "cache-status", "cache_status", "unicast-test", "unicast_test", "led-ring", "led_ring", "find-me", "find_me", "restart", "ota", "ota-progress", "ota_progress":
+	case "version", "clients", "client-info", "deadzone", "accel-deadzone", "tap-notify", "tap_notify", "cache-status", "cache_status", "unicast-test", "unicast_test", "echo-ping", "echo_ping", "led-ring", "led_ring", "find-me", "find_me", "restart", "ota", "ota-progress", "ota_progress":
 		if *portName == "" {
 			fmt.Fprintf(os.Stderr, "command %q requires -port\n\n", cmd)
 			usage()
@@ -78,6 +79,8 @@ func main() {
 			runErr = runCacheStatus(sp)
 		case "unicast-test", "unicast_test":
 			runErr = runUnicastTest(sp, flag.Args()[1:])
+		case "echo-ping", "echo_ping":
+			runErr = runEchoPing(sp, flag.Args()[1:])
 		case "led-ring", "led_ring":
 			runErr = runLedRing(sp, flag.Args()[1:])
 		case "find-me", "find_me":

goTool/pb/uart_messages.pb.go

@@ -46,6 +46,8 @@ const (
 	MessageType_TAP_NOTIFY          MessageType = 27
 	// * Combined cached accel + tap poll (one UART round-trip, ~16 ms cadence).
 	MessageType_CACHE_STATUS MessageType = 29
+	// * Host → master → slave → master: timestamp echo round-trip (latency test).
+	MessageType_ESPNOW_ECHO_PING MessageType = 30
 )
 
 // Enum value maps for MessageType.
@@ -72,6 +74,7 @@ var (
 		26: "BATTERY_STATUS",
 		27: "TAP_NOTIFY",
 		29: "CACHE_STATUS",
+		30: "ESPNOW_ECHO_PING",
 	}
 	MessageType_value = map[string]int32{
 		"UNKNOWN":             0,
@@ -95,6 +98,7 @@ var (
 		"BATTERY_STATUS":      26,
 		"TAP_NOTIFY":          27,
 		"CACHE_STATUS":        29,
+		"ESPNOW_ECHO_PING":    30,
 	}
 )
 
@@ -211,6 +215,8 @@ type UartMessage struct {
 	//	*UartMessage_TapNotifyResponse
 	//	*UartMessage_CacheStatusRequest
 	//	*UartMessage_CacheStatusResponse
+	//	*UartMessage_EspnowEchoPingRequest
+	//	*UartMessage_EspnowEchoPingResponse
 	Payload       isUartMessage_Payload `protobuf_oneof:"payload"`
 	unknownFields protoimpl.UnknownFields
 	sizeCache     protoimpl.SizeCache
@@ -521,6 +527,24 @@ func (x *UartMessage) GetCacheStatusResponse() *CacheStatusResponse {
 	return nil
 }
 
+func (x *UartMessage) GetEspnowEchoPingRequest() *EspNowEchoPingRequest {
+	if x != nil {
+		if x, ok := x.Payload.(*UartMessage_EspnowEchoPingRequest); ok {
+			return x.EspnowEchoPingRequest
+		}
+	}
+	return nil
+}
+
+func (x *UartMessage) GetEspnowEchoPingResponse() *EspNowEchoPingResponse {
+	if x != nil {
+		if x, ok := x.Payload.(*UartMessage_EspnowEchoPingResponse); ok {
+			return x.EspnowEchoPingResponse
+		}
+	}
+	return nil
+}
+
 type isUartMessage_Payload interface {
 	isUartMessage_Payload()
 }
@@ -641,6 +665,14 @@ type UartMessage_CacheStatusResponse struct {
 	CacheStatusResponse *CacheStatusResponse `protobuf:"bytes,34,opt,name=cache_status_response,json=cacheStatusResponse,proto3,oneof"`
 }
 
+type UartMessage_EspnowEchoPingRequest struct {
+	EspnowEchoPingRequest *EspNowEchoPingRequest `protobuf:"bytes,35,opt,name=espnow_echo_ping_request,json=espnowEchoPingRequest,proto3,oneof"`
+}
+
+type UartMessage_EspnowEchoPingResponse struct {
+	EspnowEchoPingResponse *EspNowEchoPingResponse `protobuf:"bytes,36,opt,name=espnow_echo_ping_response,json=espnowEchoPingResponse,proto3,oneof"`
+}
+
 func (*UartMessage_AckPayload) isUartMessage_Payload() {}
 
 func (*UartMessage_EchoPayload) isUartMessage_Payload() {}
@@ -699,6 +731,10 @@ func (*UartMessage_CacheStatusRequest) isUartMessage_Payload() {}
 
 func (*UartMessage_CacheStatusResponse) isUartMessage_Payload() {}
 
+func (*UartMessage_EspnowEchoPingRequest) isUartMessage_Payload() {}
+
+func (*UartMessage_EspnowEchoPingResponse) isUartMessage_Payload() {}
+
 type Ack struct {
 	state         protoimpl.MessageState `protogen:"open.v1"`
 	unknownFields protoimpl.UnknownFields
@@ -2329,6 +2365,130 @@ func (x *EspNowUnicastTestResponse) GetSeq() uint32 {
 	return 0
 }
 
+// * Host → master: ESP-NOW echo ping to one slave (timestamp echoed back).
+type EspNowEchoPingRequest struct {
+	state    protoimpl.MessageState `protogen:"open.v1"`
+	ClientId uint32                 `protobuf:"varint,1,opt,name=client_id,json=clientId,proto3" json:"client_id,omitempty"`
+	// * Microseconds since Unix epoch (host clock).
+	TimestampUs   uint64 `protobuf:"varint,2,opt,name=timestamp_us,json=timestampUs,proto3" json:"timestamp_us,omitempty"`
+	unknownFields protoimpl.UnknownFields
+	sizeCache     protoimpl.SizeCache
+}
+
+func (x *EspNowEchoPingRequest) Reset() {
+	*x = EspNowEchoPingRequest{}
+	mi := &file_uart_messages_proto_msgTypes[27]
+	ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+	ms.StoreMessageInfo(mi)
+}
+
+func (x *EspNowEchoPingRequest) String() string {
+	return protoimpl.X.MessageStringOf(x)
+}
+
+func (*EspNowEchoPingRequest) ProtoMessage() {}
+
+func (x *EspNowEchoPingRequest) ProtoReflect() protoreflect.Message {
+	mi := &file_uart_messages_proto_msgTypes[27]
+	if x != nil {
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		if ms.LoadMessageInfo() == nil {
+			ms.StoreMessageInfo(mi)
+		}
+		return ms
+	}
+	return mi.MessageOf(x)
+}
+
+// Deprecated: Use EspNowEchoPingRequest.ProtoReflect.Descriptor instead.
+func (*EspNowEchoPingRequest) Descriptor() ([]byte, []int) {
+	return file_uart_messages_proto_rawDescGZIP(), []int{27}
+}
+
+func (x *EspNowEchoPingRequest) GetClientId() uint32 {
+	if x != nil {
+		return x.ClientId
+	}
+	return 0
+}
+
+func (x *EspNowEchoPingRequest) GetTimestampUs() uint64 {
+	if x != nil {
+		return x.TimestampUs
+	}
+	return 0
+}
+
+type EspNowEchoPingResponse struct {
+	state    protoimpl.MessageState `protogen:"open.v1"`
+	Success  bool                   `protobuf:"varint,1,opt,name=success,proto3" json:"success,omitempty"`
+	ClientId uint32                 `protobuf:"varint,2,opt,name=client_id,json=clientId,proto3" json:"client_id,omitempty"`
+	// * Echoed host timestamp from goTool request.
+	TimestampUs uint64 `protobuf:"varint,3,opt,name=timestamp_us,json=timestampUs,proto3" json:"timestamp_us,omitempty"`
+	// * esp_timer_get_time() delta from ping send to pong recv (master→slave→master).
+	EspRttUs      uint32 `protobuf:"varint,4,opt,name=esp_rtt_us,json=espRttUs,proto3" json:"esp_rtt_us,omitempty"`
+	unknownFields protoimpl.UnknownFields
+	sizeCache     protoimpl.SizeCache
+}
+
+func (x *EspNowEchoPingResponse) Reset() {
+	*x = EspNowEchoPingResponse{}
+	mi := &file_uart_messages_proto_msgTypes[28]
+	ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+	ms.StoreMessageInfo(mi)
+}
+
+func (x *EspNowEchoPingResponse) String() string {
+	return protoimpl.X.MessageStringOf(x)
+}
+
+func (*EspNowEchoPingResponse) ProtoMessage() {}
+
+func (x *EspNowEchoPingResponse) ProtoReflect() protoreflect.Message {
+	mi := &file_uart_messages_proto_msgTypes[28]
+	if x != nil {
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		if ms.LoadMessageInfo() == nil {
+			ms.StoreMessageInfo(mi)
+		}
+		return ms
+	}
+	return mi.MessageOf(x)
+}
+
+// Deprecated: Use EspNowEchoPingResponse.ProtoReflect.Descriptor instead.
+func (*EspNowEchoPingResponse) Descriptor() ([]byte, []int) {
+	return file_uart_messages_proto_rawDescGZIP(), []int{28}
+}
+
+func (x *EspNowEchoPingResponse) GetSuccess() bool {
+	if x != nil {
+		return x.Success
+	}
+	return false
+}
+
+func (x *EspNowEchoPingResponse) GetClientId() uint32 {
+	if x != nil {
+		return x.ClientId
+	}
+	return 0
+}
+
+func (x *EspNowEchoPingResponse) GetTimestampUs() uint64 {
+	if x != nil {
+		return x.TimestampUs
+	}
+	return 0
+}
+
+func (x *EspNowEchoPingResponse) GetEspRttUs() uint32 {
+	if x != nil {
+		return x.EspRttUs
+	}
+	return 0
+}
+
 // Host → master: LED ring on master (client_id=0) and/or slaves via ESP-NOW.
 // mode: 0=clear, 1=progress (0–100 %), 2=digit (0–10), 3=blink, 4=find-me, 5=all LEDs solid color.
 type LedRingProgressRequest struct {
@@ -2359,7 +2519,7 @@ type LedRingProgressRequest struct {
 
 func (x *LedRingProgressRequest) Reset() {
 	*x = LedRingProgressRequest{}
-	mi := &file_uart_messages_proto_msgTypes[27]
+	mi := &file_uart_messages_proto_msgTypes[29]
 	ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 	ms.StoreMessageInfo(mi)
 }
@@ -2371,7 +2531,7 @@ func (x *LedRingProgressRequest) String() string {
 func (*LedRingProgressRequest) ProtoMessage() {}
 
 func (x *LedRingProgressRequest) ProtoReflect() protoreflect.Message {
-	mi := &file_uart_messages_proto_msgTypes[27]
+	mi := &file_uart_messages_proto_msgTypes[29]
 	if x != nil {
 		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 		if ms.LoadMessageInfo() == nil {
@@ -2384,7 +2544,7 @@ func (x *LedRingProgressRequest) ProtoReflect() protoreflect.Message {
 
 // Deprecated: Use LedRingProgressRequest.ProtoReflect.Descriptor instead.
 func (*LedRingProgressRequest) Descriptor() ([]byte, []int) {
-	return file_uart_messages_proto_rawDescGZIP(), []int{27}
+	return file_uart_messages_proto_rawDescGZIP(), []int{29}
 }
 
 func (x *LedRingProgressRequest) GetMode() uint32 {
@@ -2485,7 +2645,7 @@ type LedRingProgressResponse struct {
 
 func (x *LedRingProgressResponse) Reset() {
 	*x = LedRingProgressResponse{}
-	mi := &file_uart_messages_proto_msgTypes[28]
+	mi := &file_uart_messages_proto_msgTypes[30]
 	ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 	ms.StoreMessageInfo(mi)
 }
@@ -2497,7 +2657,7 @@ func (x *LedRingProgressResponse) String() string {
 func (*LedRingProgressResponse) ProtoMessage() {}
 
 func (x *LedRingProgressResponse) ProtoReflect() protoreflect.Message {
-	mi := &file_uart_messages_proto_msgTypes[28]
+	mi := &file_uart_messages_proto_msgTypes[30]
 	if x != nil {
 		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 		if ms.LoadMessageInfo() == nil {
@@ -2510,7 +2670,7 @@ func (x *LedRingProgressResponse) ProtoReflect() protoreflect.Message {
 
 // Deprecated: Use LedRingProgressResponse.ProtoReflect.Descriptor instead.
 func (*LedRingProgressResponse) Descriptor() ([]byte, []int) {
-	return file_uart_messages_proto_rawDescGZIP(), []int{28}
+	return file_uart_messages_proto_rawDescGZIP(), []int{30}
 }
 
 func (x *LedRingProgressResponse) GetSuccess() bool {
@@ -2565,7 +2725,7 @@ type EspNowFindMeRequest struct {
 
 func (x *EspNowFindMeRequest) Reset() {
 	*x = EspNowFindMeRequest{}
-	mi := &file_uart_messages_proto_msgTypes[29]
+	mi := &file_uart_messages_proto_msgTypes[31]
 	ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 	ms.StoreMessageInfo(mi)
 }
@@ -2577,7 +2737,7 @@ func (x *EspNowFindMeRequest) String() string {
 func (*EspNowFindMeRequest) ProtoMessage() {}
 
 func (x *EspNowFindMeRequest) ProtoReflect() protoreflect.Message {
-	mi := &file_uart_messages_proto_msgTypes[29]
+	mi := &file_uart_messages_proto_msgTypes[31]
 	if x != nil {
 		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 		if ms.LoadMessageInfo() == nil {
@@ -2590,7 +2750,7 @@ func (x *EspNowFindMeRequest) ProtoReflect() protoreflect.Message {
 
 // Deprecated: Use EspNowFindMeRequest.ProtoReflect.Descriptor instead.
 func (*EspNowFindMeRequest) Descriptor() ([]byte, []int) {
-	return file_uart_messages_proto_rawDescGZIP(), []int{29}
+	return file_uart_messages_proto_rawDescGZIP(), []int{31}
 }
 
 func (x *EspNowFindMeRequest) GetClientId() uint32 {
@@ -2610,7 +2770,7 @@ type EspNowFindMeResponse struct {
 
 func (x *EspNowFindMeResponse) Reset() {
 	*x = EspNowFindMeResponse{}
-	mi := &file_uart_messages_proto_msgTypes[30]
+	mi := &file_uart_messages_proto_msgTypes[32]
 	ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 	ms.StoreMessageInfo(mi)
 }
@@ -2622,7 +2782,7 @@ func (x *EspNowFindMeResponse) String() string {
 func (*EspNowFindMeResponse) ProtoMessage() {}
 
 func (x *EspNowFindMeResponse) ProtoReflect() protoreflect.Message {
-	mi := &file_uart_messages_proto_msgTypes[30]
+	mi := &file_uart_messages_proto_msgTypes[32]
 	if x != nil {
 		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 		if ms.LoadMessageInfo() == nil {
@@ -2635,7 +2795,7 @@ func (x *EspNowFindMeResponse) ProtoReflect() protoreflect.Message {
 
 // Deprecated: Use EspNowFindMeResponse.ProtoReflect.Descriptor instead.
 func (*EspNowFindMeResponse) Descriptor() ([]byte, []int) {
-	return file_uart_messages_proto_rawDescGZIP(), []int{30}
+	return file_uart_messages_proto_rawDescGZIP(), []int{32}
 }
 
 func (x *EspNowFindMeResponse) GetSuccess() bool {
@@ -2662,7 +2822,7 @@ type RestartRequest struct {
 
 func (x *RestartRequest) Reset() {
 	*x = RestartRequest{}
-	mi := &file_uart_messages_proto_msgTypes[31]
+	mi := &file_uart_messages_proto_msgTypes[33]
 	ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 	ms.StoreMessageInfo(mi)
 }
@@ -2674,7 +2834,7 @@ func (x *RestartRequest) String() string {
 func (*RestartRequest) ProtoMessage() {}
 
 func (x *RestartRequest) ProtoReflect() protoreflect.Message {
-	mi := &file_uart_messages_proto_msgTypes[31]
+	mi := &file_uart_messages_proto_msgTypes[33]
 	if x != nil {
 		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 		if ms.LoadMessageInfo() == nil {
@@ -2687,7 +2847,7 @@ func (x *RestartRequest) ProtoReflect() protoreflect.Message {
 
 // Deprecated: Use RestartRequest.ProtoReflect.Descriptor instead.
 func (*RestartRequest) Descriptor() ([]byte, []int) {
-	return file_uart_messages_proto_rawDescGZIP(), []int{31}
+	return file_uart_messages_proto_rawDescGZIP(), []int{33}
 }
 
 func (x *RestartRequest) GetClientId() uint32 {
@@ -2707,7 +2867,7 @@ type RestartResponse struct {
 
 func (x *RestartResponse) Reset() {
 	*x = RestartResponse{}
-	mi := &file_uart_messages_proto_msgTypes[32]
+	mi := &file_uart_messages_proto_msgTypes[34]
 	ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 	ms.StoreMessageInfo(mi)
 }
@@ -2719,7 +2879,7 @@ func (x *RestartResponse) String() string {
 func (*RestartResponse) ProtoMessage() {}
 
 func (x *RestartResponse) ProtoReflect() protoreflect.Message {
-	mi := &file_uart_messages_proto_msgTypes[32]
+	mi := &file_uart_messages_proto_msgTypes[34]
 	if x != nil {
 		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 		if ms.LoadMessageInfo() == nil {
@@ -2732,7 +2892,7 @@ func (x *RestartResponse) ProtoReflect() protoreflect.Message {
 
 // Deprecated: Use RestartResponse.ProtoReflect.Descriptor instead.
 func (*RestartResponse) Descriptor() ([]byte, []int) {
-	return file_uart_messages_proto_rawDescGZIP(), []int{32}
+	return file_uart_messages_proto_rawDescGZIP(), []int{34}
 }
 
 func (x *RestartResponse) GetSuccess() bool {
@@ -2759,7 +2919,7 @@ type OtaStartPayload struct {
 
 func (x *OtaStartPayload) Reset() {
 	*x = OtaStartPayload{}
-	mi := &file_uart_messages_proto_msgTypes[33]
+	mi := &file_uart_messages_proto_msgTypes[35]
 	ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 	ms.StoreMessageInfo(mi)
 }
@@ -2771,7 +2931,7 @@ func (x *OtaStartPayload) String() string {
 func (*OtaStartPayload) ProtoMessage() {}
 
 func (x *OtaStartPayload) ProtoReflect() protoreflect.Message {
-	mi := &file_uart_messages_proto_msgTypes[33]
+	mi := &file_uart_messages_proto_msgTypes[35]
 	if x != nil {
 		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 		if ms.LoadMessageInfo() == nil {
@@ -2784,7 +2944,7 @@ func (x *OtaStartPayload) ProtoReflect() protoreflect.Message {
 
 // Deprecated: Use OtaStartPayload.ProtoReflect.Descriptor instead.
 func (*OtaStartPayload) Descriptor() ([]byte, []int) {
-	return file_uart_messages_proto_rawDescGZIP(), []int{33}
+	return file_uart_messages_proto_rawDescGZIP(), []int{35}
 }
 
 func (x *OtaStartPayload) GetTotalSize() uint32 {
@@ -2805,7 +2965,7 @@ type OtaPayload struct {
 
 func (x *OtaPayload) Reset() {
 	*x = OtaPayload{}
-	mi := &file_uart_messages_proto_msgTypes[34]
+	mi := &file_uart_messages_proto_msgTypes[36]
 	ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 	ms.StoreMessageInfo(mi)
 }
@@ -2817,7 +2977,7 @@ func (x *OtaPayload) String() string {
 func (*OtaPayload) ProtoMessage() {}
 
 func (x *OtaPayload) ProtoReflect() protoreflect.Message {
-	mi := &file_uart_messages_proto_msgTypes[34]
+	mi := &file_uart_messages_proto_msgTypes[36]
 	if x != nil {
 		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 		if ms.LoadMessageInfo() == nil {
@@ -2830,7 +2990,7 @@ func (x *OtaPayload) ProtoReflect() protoreflect.Message {
 
 // Deprecated: Use OtaPayload.ProtoReflect.Descriptor instead.
 func (*OtaPayload) Descriptor() ([]byte, []int) {
-	return file_uart_messages_proto_rawDescGZIP(), []int{34}
+	return file_uart_messages_proto_rawDescGZIP(), []int{36}
 }
 
 func (x *OtaPayload) GetSeq() uint32 {
@@ -2856,7 +3016,7 @@ type OtaEndPayload struct {
 
 func (x *OtaEndPayload) Reset() {
 	*x = OtaEndPayload{}
-	mi := &file_uart_messages_proto_msgTypes[35]
+	mi := &file_uart_messages_proto_msgTypes[37]
 	ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 	ms.StoreMessageInfo(mi)
 }
@@ -2868,7 +3028,7 @@ func (x *OtaEndPayload) String() string {
 func (*OtaEndPayload) ProtoMessage() {}
 
 func (x *OtaEndPayload) ProtoReflect() protoreflect.Message {
-	mi := &file_uart_messages_proto_msgTypes[35]
+	mi := &file_uart_messages_proto_msgTypes[37]
 	if x != nil {
 		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 		if ms.LoadMessageInfo() == nil {
@@ -2881,7 +3041,7 @@ func (x *OtaEndPayload) ProtoReflect() protoreflect.Message {
 
 // Deprecated: Use OtaEndPayload.ProtoReflect.Descriptor instead.
 func (*OtaEndPayload) Descriptor() ([]byte, []int) {
-	return file_uart_messages_proto_rawDescGZIP(), []int{35}
+	return file_uart_messages_proto_rawDescGZIP(), []int{37}
 }
 
 // Device → host status (also used as ACK after each 4 KiB written).
@@ -2898,7 +3058,7 @@ type OtaStatusPayload struct {
 
 func (x *OtaStatusPayload) Reset() {
 	*x = OtaStatusPayload{}
-	mi := &file_uart_messages_proto_msgTypes[36]
+	mi := &file_uart_messages_proto_msgTypes[38]
 	ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 	ms.StoreMessageInfo(mi)
 }
@@ -2910,7 +3070,7 @@ func (x *OtaStatusPayload) String() string {
 func (*OtaStatusPayload) ProtoMessage() {}
 
 func (x *OtaStatusPayload) ProtoReflect() protoreflect.Message {
-	mi := &file_uart_messages_proto_msgTypes[36]
+	mi := &file_uart_messages_proto_msgTypes[38]
 	if x != nil {
 		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 		if ms.LoadMessageInfo() == nil {
@@ -2923,7 +3083,7 @@ func (x *OtaStatusPayload) ProtoReflect() protoreflect.Message {
 
 // Deprecated: Use OtaStatusPayload.ProtoReflect.Descriptor instead.
 func (*OtaStatusPayload) Descriptor() ([]byte, []int) {
-	return file_uart_messages_proto_rawDescGZIP(), []int{36}
+	return file_uart_messages_proto_rawDescGZIP(), []int{38}
 }
 
 func (x *OtaStatusPayload) GetStatus() uint32 {
@@ -2964,7 +3124,7 @@ type OtaSlaveProgressRequest struct {
 
 func (x *OtaSlaveProgressRequest) Reset() {
 	*x = OtaSlaveProgressRequest{}
-	mi := &file_uart_messages_proto_msgTypes[37]
+	mi := &file_uart_messages_proto_msgTypes[39]
 	ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 	ms.StoreMessageInfo(mi)
 }
@@ -2976,7 +3136,7 @@ func (x *OtaSlaveProgressRequest) String() string {
 func (*OtaSlaveProgressRequest) ProtoMessage() {}
 
 func (x *OtaSlaveProgressRequest) ProtoReflect() protoreflect.Message {
-	mi := &file_uart_messages_proto_msgTypes[37]
+	mi := &file_uart_messages_proto_msgTypes[39]
 	if x != nil {
 		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 		if ms.LoadMessageInfo() == nil {
@@ -2989,7 +3149,7 @@ func (x *OtaSlaveProgressRequest) ProtoReflect() protoreflect.Message {
 
 // Deprecated: Use OtaSlaveProgressRequest.ProtoReflect.Descriptor instead.
 func (*OtaSlaveProgressRequest) Descriptor() ([]byte, []int) {
-	return file_uart_messages_proto_rawDescGZIP(), []int{37}
+	return file_uart_messages_proto_rawDescGZIP(), []int{39}
 }
 
 func (x *OtaSlaveProgressRequest) GetClientId() uint32 {
@@ -3013,7 +3173,7 @@ type OtaSlaveProgressEntry struct {
 
 func (x *OtaSlaveProgressEntry) Reset() {
 	*x = OtaSlaveProgressEntry{}
-	mi := &file_uart_messages_proto_msgTypes[38]
+	mi := &file_uart_messages_proto_msgTypes[40]
 	ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 	ms.StoreMessageInfo(mi)
 }
@@ -3025,7 +3185,7 @@ func (x *OtaSlaveProgressEntry) String() string {
 func (*OtaSlaveProgressEntry) ProtoMessage() {}
 
 func (x *OtaSlaveProgressEntry) ProtoReflect() protoreflect.Message {
-	mi := &file_uart_messages_proto_msgTypes[38]
+	mi := &file_uart_messages_proto_msgTypes[40]
 	if x != nil {
 		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 		if ms.LoadMessageInfo() == nil {
@@ -3038,7 +3198,7 @@ func (x *OtaSlaveProgressEntry) ProtoReflect() protoreflect.Message {
 
 // Deprecated: Use OtaSlaveProgressEntry.ProtoReflect.Descriptor instead.
 func (*OtaSlaveProgressEntry) Descriptor() ([]byte, []int) {
-	return file_uart_messages_proto_rawDescGZIP(), []int{38}
+	return file_uart_messages_proto_rawDescGZIP(), []int{40}
 }
 
 func (x *OtaSlaveProgressEntry) GetClientId() uint32 {
@@ -3089,7 +3249,7 @@ type OtaSlaveProgressResponse struct {
 
 func (x *OtaSlaveProgressResponse) Reset() {
 	*x = OtaSlaveProgressResponse{}
-	mi := &file_uart_messages_proto_msgTypes[39]
+	mi := &file_uart_messages_proto_msgTypes[41]
 	ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 	ms.StoreMessageInfo(mi)
 }
@@ -3101,7 +3261,7 @@ func (x *OtaSlaveProgressResponse) String() string {
 func (*OtaSlaveProgressResponse) ProtoMessage() {}
 
 func (x *OtaSlaveProgressResponse) ProtoReflect() protoreflect.Message {
-	mi := &file_uart_messages_proto_msgTypes[39]
+	mi := &file_uart_messages_proto_msgTypes[41]
 	if x != nil {
 		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 		if ms.LoadMessageInfo() == nil {
@@ -3114,7 +3274,7 @@ func (x *OtaSlaveProgressResponse) ProtoReflect() protoreflect.Message {
 
 // Deprecated: Use OtaSlaveProgressResponse.ProtoReflect.Descriptor instead.
 func (*OtaSlaveProgressResponse) Descriptor() ([]byte, []int) {
-	return file_uart_messages_proto_rawDescGZIP(), []int{39}
+	return file_uart_messages_proto_rawDescGZIP(), []int{41}
 }
 
 func (x *OtaSlaveProgressResponse) GetActive() bool {
@@ -3156,7 +3316,7 @@ var File_uart_messages_proto protoreflect.FileDescriptor
 
 const file_uart_messages_proto_rawDesc = "" +
 	"\n" +
-	"\x13uart_messages.proto\x12\x04alox\x1a\fnanopb.proto\"\xec\x11\n" +
+	"\x13uart_messages.proto\x12\x04alox\x1a\fnanopb.proto\"\x9f\x13\n" +
 	"\vUartMessage\x12%\n" +
 	"\x04type\x18\x01 \x01(\x0e2\x11.alox.MessageTypeR\x04type\x12,\n" +
 	"\vack_payload\x18\x02 \x01(\v2\t.alox.AckH\x00R\n" +
@@ -3191,7 +3351,9 @@ const file_uart_messages_proto_rawDesc = "" +
 	"\x12tap_notify_request\x18\x1d \x01(\v2\x16.alox.TapNotifyRequestH\x00R\x10tapNotifyRequest\x12I\n" +
 	"\x13tap_notify_response\x18\x1e \x01(\v2\x17.alox.TapNotifyResponseH\x00R\x11tapNotifyResponse\x12L\n" +
 	"\x14cache_status_request\x18! \x01(\v2\x18.alox.CacheStatusRequestH\x00R\x12cacheStatusRequest\x12O\n" +
-	"\x15cache_status_response\x18\" \x01(\v2\x19.alox.CacheStatusResponseH\x00R\x13cacheStatusResponseB\t\n" +
+	"\x15cache_status_response\x18\" \x01(\v2\x19.alox.CacheStatusResponseH\x00R\x13cacheStatusResponse\x12V\n" +
+	"\x18espnow_echo_ping_request\x18# \x01(\v2\x1b.alox.EspNowEchoPingRequestH\x00R\x15espnowEchoPingRequest\x12Y\n" +
+	"\x19espnow_echo_ping_response\x18$ \x01(\v2\x1c.alox.EspNowEchoPingResponseH\x00R\x16espnowEchoPingResponseB\t\n" +
 	"\apayload\"\x05\n" +
 	"\x03Ack\"!\n" +
 	"\vEchoPayload\x12\x12\n" +
@@ -3311,7 +3473,16 @@ const file_uart_messages_proto_rawDesc = "" +
 	"\x03seq\x18\x02 \x01(\rR\x03seq\"G\n" +
 	"\x19EspNowUnicastTestResponse\x12\x18\n" +
 	"\asuccess\x18\x01 \x01(\bR\asuccess\x12\x10\n" +
-	"\x03seq\x18\x02 \x01(\rR\x03seq\"\xc1\x02\n" +
+	"\x03seq\x18\x02 \x01(\rR\x03seq\"W\n" +
+	"\x15EspNowEchoPingRequest\x12\x1b\n" +
+	"\tclient_id\x18\x01 \x01(\rR\bclientId\x12!\n" +
+	"\ftimestamp_us\x18\x02 \x01(\x04R\vtimestampUs\"\x90\x01\n" +
+	"\x16EspNowEchoPingResponse\x12\x18\n" +
+	"\asuccess\x18\x01 \x01(\bR\asuccess\x12\x1b\n" +
+	"\tclient_id\x18\x02 \x01(\rR\bclientId\x12!\n" +
+	"\ftimestamp_us\x18\x03 \x01(\x04R\vtimestampUs\x12\x1c\n" +
+	"\n" +
+	"esp_rtt_us\x18\x04 \x01(\rR\bespRttUs\"\xc1\x02\n" +
 	"\x16LedRingProgressRequest\x12\x12\n" +
 	"\x04mode\x18\x01 \x01(\rR\x04mode\x12\x1a\n" +
 	"\bprogress\x18\x02 \x01(\rR\bprogress\x12\x14\n" +
@@ -3376,7 +3547,7 @@ const file_uart_messages_proto_rawDesc = "" +
 	"\x0faggregate_bytes\x18\x03 \x01(\rR\x0eaggregateBytes\x12\x1f\n" +
 	"\vslave_count\x18\x04 \x01(\rR\n" +
 	"slaveCount\x12:\n" +
-	"\x06slaves\x18\x05 \x03(\v2\x1b.alox.OtaSlaveProgressEntryB\x05\x92?\x02\x10\x10R\x06slaves*\xf1\x02\n" +
+	"\x06slaves\x18\x05 \x03(\v2\x1b.alox.OtaSlaveProgressEntryB\x05\x92?\x02\x10\x10R\x06slaves*\x87\x03\n" +
 	"\vMessageType\x12\v\n" +
 	"\aUNKNOWN\x10\x00\x12\a\n" +
 	"\x03ACK\x10\x01\x12\b\n" +
@@ -3400,7 +3571,8 @@ const file_uart_messages_proto_rawDesc = "" +
 	"\x0eBATTERY_STATUS\x10\x1a\x12\x0e\n" +
 	"\n" +
 	"TAP_NOTIFY\x10\x1b\x12\x10\n" +
-	"\fCACHE_STATUS\x10\x1d\"\x04\b\x18\x10\x18\"\x04\b\x1c\x10\x1c*G\n" +
+	"\fCACHE_STATUS\x10\x1d\x12\x14\n" +
+	"\x10ESPNOW_ECHO_PING\x10\x1e\"\x04\b\x18\x10\x18\"\x04\b\x1c\x10\x1c*G\n" +
 	"\aTapKind\x12\f\n" +
 	"\bTAP_NONE\x10\x00\x12\x0e\n" +
 	"\n" +
@@ -3423,7 +3595,7 @@ func file_uart_messages_proto_rawDescGZIP() []byte {
 }
 
 var file_uart_messages_proto_enumTypes = make([]protoimpl.EnumInfo, 2)
-var file_uart_messages_proto_msgTypes = make([]protoimpl.MessageInfo, 40)
+var file_uart_messages_proto_msgTypes = make([]protoimpl.MessageInfo, 42)
 var file_uart_messages_proto_goTypes = []any{
 	(MessageType)(0),                  // 0: alox.MessageType
 	(TapKind)(0),                      // 1: alox.TapKind
@@ -3454,19 +3626,21 @@ var file_uart_messages_proto_goTypes = []any{
 	(*CacheStatusResponse)(nil),       // 26: alox.CacheStatusResponse
 	(*EspNowUnicastTestRequest)(nil),  // 27: alox.EspNowUnicastTestRequest
 	(*EspNowUnicastTestResponse)(nil), // 28: alox.EspNowUnicastTestResponse
-	(*LedRingProgressRequest)(nil),    // 29: alox.LedRingProgressRequest
+	(*EspNowEchoPingRequest)(nil),     // 29: alox.EspNowEchoPingRequest
-	(*LedRingProgressResponse)(nil),   // 30: alox.LedRingProgressResponse
+	(*EspNowEchoPingResponse)(nil),    // 30: alox.EspNowEchoPingResponse
-	(*EspNowFindMeRequest)(nil),       // 31: alox.EspNowFindMeRequest
+	(*LedRingProgressRequest)(nil),    // 31: alox.LedRingProgressRequest
-	(*EspNowFindMeResponse)(nil),      // 32: alox.EspNowFindMeResponse
+	(*LedRingProgressResponse)(nil),   // 32: alox.LedRingProgressResponse
-	(*RestartRequest)(nil),            // 33: alox.RestartRequest
+	(*EspNowFindMeRequest)(nil),       // 33: alox.EspNowFindMeRequest
-	(*RestartResponse)(nil),           // 34: alox.RestartResponse
+	(*EspNowFindMeResponse)(nil),      // 34: alox.EspNowFindMeResponse
-	(*OtaStartPayload)(nil),           // 35: alox.OtaStartPayload
+	(*RestartRequest)(nil),            // 35: alox.RestartRequest
-	(*OtaPayload)(nil),                // 36: alox.OtaPayload
+	(*RestartResponse)(nil),           // 36: alox.RestartResponse
-	(*OtaEndPayload)(nil),             // 37: alox.OtaEndPayload
+	(*OtaStartPayload)(nil),           // 37: alox.OtaStartPayload
-	(*OtaStatusPayload)(nil),          // 38: alox.OtaStatusPayload
+	(*OtaPayload)(nil),                // 38: alox.OtaPayload
-	(*OtaSlaveProgressRequest)(nil),   // 39: alox.OtaSlaveProgressRequest
+	(*OtaEndPayload)(nil),             // 39: alox.OtaEndPayload
-	(*OtaSlaveProgressEntry)(nil),     // 40: alox.OtaSlaveProgressEntry
+	(*OtaStatusPayload)(nil),          // 40: alox.OtaStatusPayload
-	(*OtaSlaveProgressResponse)(nil),  // 41: alox.OtaSlaveProgressResponse
+	(*OtaSlaveProgressRequest)(nil),   // 41: alox.OtaSlaveProgressRequest
+	(*OtaSlaveProgressEntry)(nil),     // 42: alox.OtaSlaveProgressEntry
+	(*OtaSlaveProgressResponse)(nil),  // 43: alox.OtaSlaveProgressResponse
 }
 var file_uart_messages_proto_depIdxs = []int32{
 	0,  // 0: alox.UartMessage.type:type_name -> alox.MessageType
@@ -3475,22 +3649,22 @@ var file_uart_messages_proto_depIdxs = []int32{
 	5,  // 3: alox.UartMessage.version_response:type_name -> alox.VersionResponse
 	7,  // 4: alox.UartMessage.client_info_response:type_name -> alox.ClientInfoResponse
 	9,  // 5: alox.UartMessage.client_input_response:type_name -> alox.ClientInputResponse
-	35, // 6: alox.UartMessage.ota_start:type_name -> alox.OtaStartPayload
+	37, // 6: alox.UartMessage.ota_start:type_name -> alox.OtaStartPayload
-	36, // 7: alox.UartMessage.ota_payload:type_name -> alox.OtaPayload
+	38, // 7: alox.UartMessage.ota_payload:type_name -> alox.OtaPayload
-	37, // 8: alox.UartMessage.ota_end:type_name -> alox.OtaEndPayload
+	39, // 8: alox.UartMessage.ota_end:type_name -> alox.OtaEndPayload
-	38, // 9: alox.UartMessage.ota_status:type_name -> alox.OtaStatusPayload
+	40, // 9: alox.UartMessage.ota_status:type_name -> alox.OtaStatusPayload
 	10, // 10: alox.UartMessage.accel_deadzone_request:type_name -> alox.AccelDeadzoneRequest
 	11, // 11: alox.UartMessage.accel_deadzone_response:type_name -> alox.AccelDeadzoneResponse
 	27, // 12: alox.UartMessage.espnow_unicast_test_request:type_name -> alox.EspNowUnicastTestRequest
 	28, // 13: alox.UartMessage.espnow_unicast_test_response:type_name -> alox.EspNowUnicastTestResponse
-	39, // 14: alox.UartMessage.ota_slave_progress_request:type_name -> alox.OtaSlaveProgressRequest
+	41, // 14: alox.UartMessage.ota_slave_progress_request:type_name -> alox.OtaSlaveProgressRequest
-	41, // 15: alox.UartMessage.ota_slave_progress_response:type_name -> alox.OtaSlaveProgressResponse
+	43, // 15: alox.UartMessage.ota_slave_progress_response:type_name -> alox.OtaSlaveProgressResponse
-	29, // 16: alox.UartMessage.led_ring_progress_request:type_name -> alox.LedRingProgressRequest
+	31, // 16: alox.UartMessage.led_ring_progress_request:type_name -> alox.LedRingProgressRequest
-	30, // 17: alox.UartMessage.led_ring_progress_response:type_name -> alox.LedRingProgressResponse
+	32, // 17: alox.UartMessage.led_ring_progress_response:type_name -> alox.LedRingProgressResponse
-	31, // 18: alox.UartMessage.espnow_find_me_request:type_name -> alox.EspNowFindMeRequest
+	33, // 18: alox.UartMessage.espnow_find_me_request:type_name -> alox.EspNowFindMeRequest
-	32, // 19: alox.UartMessage.espnow_find_me_response:type_name -> alox.EspNowFindMeResponse
+	34, // 19: alox.UartMessage.espnow_find_me_response:type_name -> alox.EspNowFindMeResponse
-	33, // 20: alox.UartMessage.restart_request:type_name -> alox.RestartRequest
+	35, // 20: alox.UartMessage.restart_request:type_name -> alox.RestartRequest
-	34, // 21: alox.UartMessage.restart_response:type_name -> alox.RestartResponse
+	36, // 21: alox.UartMessage.restart_response:type_name -> alox.RestartResponse
 	12, // 22: alox.UartMessage.accel_stream_request:type_name -> alox.AccelStreamRequest
 	13, // 23: alox.UartMessage.accel_stream_response:type_name -> alox.AccelStreamResponse
 	14, // 24: alox.UartMessage.battery_status_request:type_name -> alox.BatteryStatusRequest
@@ -3499,22 +3673,24 @@ var file_uart_messages_proto_depIdxs = []int32{
 	20, // 27: alox.UartMessage.tap_notify_response:type_name -> alox.TapNotifyResponse
 	22, // 28: alox.UartMessage.cache_status_request:type_name -> alox.CacheStatusRequest
 	26, // 29: alox.UartMessage.cache_status_response:type_name -> alox.CacheStatusResponse
-	6,  // 30: alox.ClientInfoResponse.clients:type_name -> alox.ClientInfo
+	29, // 30: alox.UartMessage.espnow_echo_ping_request:type_name -> alox.EspNowEchoPingRequest
-	8,  // 31: alox.ClientInputResponse.clients:type_name -> alox.ClientInput
+	30, // 31: alox.UartMessage.espnow_echo_ping_response:type_name -> alox.EspNowEchoPingResponse
-	15, // 32: alox.BatterySample.lipo1:type_name -> alox.LipoReading
+	6,  // 32: alox.ClientInfoResponse.clients:type_name -> alox.ClientInfo
-	15, // 33: alox.BatterySample.lipo2:type_name -> alox.LipoReading
+	8,  // 33: alox.ClientInputResponse.clients:type_name -> alox.ClientInput
-	16, // 34: alox.BatteryStatusResponse.samples:type_name -> alox.BatterySample
+	15, // 34: alox.BatterySample.lipo1:type_name -> alox.LipoReading
-	1,  // 35: alox.TapEvent.kind:type_name -> alox.TapKind
+	15, // 35: alox.BatterySample.lipo2:type_name -> alox.LipoReading
-	1,  // 36: alox.CacheClientTap.kind:type_name -> alox.TapKind
+	16, // 36: alox.BatteryStatusResponse.samples:type_name -> alox.BatterySample
-	23, // 37: alox.CacheClientStatus.accel:type_name -> alox.CacheClientAccel
+	1,  // 37: alox.TapEvent.kind:type_name -> alox.TapKind
-	24, // 38: alox.CacheClientStatus.tap:type_name -> alox.CacheClientTap
+	1,  // 38: alox.CacheClientTap.kind:type_name -> alox.TapKind
-	25, // 39: alox.CacheStatusResponse.clients:type_name -> alox.CacheClientStatus
+	23, // 39: alox.CacheClientStatus.accel:type_name -> alox.CacheClientAccel
-	40, // 40: alox.OtaSlaveProgressResponse.slaves:type_name -> alox.OtaSlaveProgressEntry
+	24, // 40: alox.CacheClientStatus.tap:type_name -> alox.CacheClientTap
-	41, // [41:41] is the sub-list for method output_type
+	25, // 41: alox.CacheStatusResponse.clients:type_name -> alox.CacheClientStatus
-	41, // [41:41] is the sub-list for method input_type
+	42, // 42: alox.OtaSlaveProgressResponse.slaves:type_name -> alox.OtaSlaveProgressEntry
-	41, // [41:41] is the sub-list for extension type_name
+	43, // [43:43] is the sub-list for method output_type
-	41, // [41:41] is the sub-list for extension extendee
+	43, // [43:43] is the sub-list for method input_type
-	0,  // [0:41] is the sub-list for field type_name
+	43, // [43:43] is the sub-list for extension type_name
+	43, // [43:43] is the sub-list for extension extendee
+	0,  // [0:43] is the sub-list for field type_name
 }
 
 func init() { file_uart_messages_proto_init() }
@@ -3552,6 +3728,8 @@ func file_uart_messages_proto_init() {
 		(*UartMessage_TapNotifyResponse)(nil),
 		(*UartMessage_CacheStatusRequest)(nil),
 		(*UartMessage_CacheStatusResponse)(nil),
+		(*UartMessage_EspnowEchoPingRequest)(nil),
+		(*UartMessage_EspnowEchoPingResponse)(nil),
 	}
 	type x struct{}
 	out := protoimpl.TypeBuilder{
@@ -3559,7 +3737,7 @@ func file_uart_messages_proto_init() {
 			GoPackagePath: reflect.TypeOf(x{}).PkgPath(),
 			RawDescriptor: unsafe.Slice(unsafe.StringData(file_uart_messages_proto_rawDesc), len(file_uart_messages_proto_rawDesc)),
 			NumEnums:      2,
-			NumMessages:   40,
+			NumMessages:   42,
 			NumExtensions: 0,
 			NumServices:   0,
 		},

goTool/webui/index.html

@@ -403,6 +403,12 @@
                                   title="ESP-NOW Unicast-Test">
                             Test
                           </button>
+                          <button type="button" class="btn btn-outline-info btn-sm"
+                                  @click="echoPing(c.id)"
+                                  :disabled="busy || !state.uart_connected || !c.available"
+                                  title="ESP-NOW Timestamp-Echo (Round-Trip-Latenz)">
+                            Ping
+                          </button>
                           <button type="button" class="btn btn-outline-info btn-sm"
                                   @click="ledRing({ clientId: c.id })"
                                   :disabled="busy || !state.uart_connected || !c.available"
@@ -640,6 +646,7 @@
         busy: false,
         configMsg: '',
         configMsgOk: false,
+        _flashTimer: null,
         led: {
           mode: 'color',
           r: 0,
@@ -1031,10 +1038,14 @@
             this.busy = false;
           }
         },
-        flash(msg, ok) {
+        flash(msg, ok, durationMs = 5000) {
           this.configMsg = msg;
           this.configMsgOk = ok;
-          setTimeout(() => { this.configMsg = ''; }, 5000);
+          if (this._flashTimer) clearTimeout(this._flashTimer);
+          this._flashTimer = setTimeout(() => {
+            this.configMsg = '';
+            this._flashTimer = null;
+          }, durationMs);
         },
         async setDeadzone(clientId, deadzone, opts = {}) {
           if (deadzone == null || deadzone < 0) {
@@ -1258,6 +1269,43 @@
             this.busy = false;
           }
         },
+        formatMs(v) {
+          return v != null && Number.isFinite(Number(v)) ? Number(v).toFixed(3) : '—';
+        },
+        formatUsAsMs(us) {
+          return us != null && Number.isFinite(Number(us))
+            ? (Number(us) / 1000).toFixed(3)
+            : '—';
+        },
+        async echoPing(clientId) {
+          this.busy = true;
+          try {
+            const r = await fetch('/api/echo-ping', {
+              method: 'POST',
+              headers: { 'Content-Type': 'application/json' },
+              body: JSON.stringify({ client_id: clientId })
+            });
+            const data = await r.json();
+            if (!r.ok) {
+              this.flash(data.error || `Echo-Ping Slave ${clientId} fehlgeschlagen`, false);
+              return;
+            }
+            if (!data.success) {
+              this.flash(`Echo-Ping Slave ${clientId} fehlgeschlagen (${this.formatMs(data.rtt_ms)} ms)`, false);
+              return;
+            }
+            this.flash(
+              `Echo-Ping Slave ${clientId}: Host ${this.formatMs(data.rtt_ms)} ms, ` +
+              `ESP ${this.formatUsAsMs(data.esp_rtt_us)} ms`,
+              true,
+              5000
+            );
+          } catch (e) {
+            this.flash(String(e), false);
+          } finally {
+            this.busy = false;
+          }
+        },
         async restart(clientId = 0) {
           this.busy = true;
           try {

main/CMakeLists.txt

@@ -22,6 +22,7 @@ idf_component_register(
   "cmd/cmd_tap_notify.c"
   "cmd/cmd_cache_status.c"
   "cmd/cmd_espnow_unicast_test.c"
+  "cmd/cmd_espnow_echo_ping.c"
   "cmd/cmd_espnow_find_me.c"
   "cmd/cmd_restart.c"
   "pod_reboot.c"
@@ -61,6 +62,7 @@ idf_component_register(
   esp_driver_i2c
   esp_adc
   app_update
+  esp_timer
   bma456)
 
 target_compile_definitions(${COMPONENT_LIB}

main/cmd/cmd_espnow_echo_ping.c

@@ -0,0 +1,70 @@
+#include "client_registry.h"
+#include "cmd_espnow_echo_ping.h"
+#include "esp_log.h"
+#include "esp_now_comm.h"
+#include "uart_cmd.h"
+
+static const char *TAG = "[ECHO_PING]";
+
+static void reply(bool success, uint32_t client_id, uint64_t timestamp_us,
+                  uint32_t esp_rtt_us) {
+  alox_UartMessage response;
+  uart_cmd_init_response(&response, alox_MessageType_ESPNOW_ECHO_PING,
+                         alox_UartMessage_espnow_echo_ping_response_tag);
+  response.payload.espnow_echo_ping_response.success = success;
+  response.payload.espnow_echo_ping_response.client_id = client_id;
+  response.payload.espnow_echo_ping_response.timestamp_us = timestamp_us;
+  response.payload.espnow_echo_ping_response.esp_rtt_us = esp_rtt_us;
+  uart_cmd_send(&response, TAG);
+}
+
+static void handle_espnow_echo_ping(const uint8_t *data, size_t len) {
+  alox_UartMessage uart_msg;
+
+  if (uart_cmd_decode(data, len, &uart_msg) != ESP_OK) {
+    ESP_LOGW(TAG, "decode failed");
+    reply(false, 0, 0, 0);
+    return;
+  }
+
+  const alox_EspNowEchoPingRequest *req = UART_CMD_REQ(
+      &uart_msg, alox_UartMessage_espnow_echo_ping_request_tag,
+      espnow_echo_ping_request);
+  if (req == NULL || req->client_id == 0) {
+    ESP_LOGW(TAG, "need client_id in request");
+    reply(false, 0, 0, 0);
+    return;
+  }
+
+  const client_info_t *client = client_registry_find_by_id(req->client_id);
+  if (client == NULL) {
+    ESP_LOGW(TAG, "client id %lu not in registry",
+             (unsigned long)req->client_id);
+    reply(false, req->client_id, 0, 0);
+    return;
+  }
+
+  ESP_LOGI(TAG, "UART request client_id=%lu host_ts=%llu",
+           (unsigned long)req->client_id,
+           (unsigned long long)req->timestamp_us);
+
+  esp_now_echo_ping_result_t ping_result = {0};
+  esp_err_t err =
+      esp_now_comm_echo_ping(client->mac, req->timestamp_us, &ping_result);
+  if (err != ESP_OK) {
+    ESP_LOGW(TAG, "echo ping to id=%lu failed: %s", (unsigned long)req->client_id,
+             esp_err_to_name(err));
+    reply(false, req->client_id, 0, 0);
+    return;
+  }
+
+  ESP_LOGI(TAG, "UART reply client_id=%lu host_ts=%llu esp_rtt_us=%lu",
+           (unsigned long)req->client_id,
+           (unsigned long long)ping_result.echoed_us,
+           (unsigned long)ping_result.esp_rtt_us);
+  reply(true, req->client_id, ping_result.echoed_us, ping_result.esp_rtt_us);
+}
+
+void cmd_espnow_echo_ping_register(void) {
+  uart_cmd_register(alox_MessageType_ESPNOW_ECHO_PING, handle_espnow_echo_ping);
+}

main/cmd/cmd_espnow_echo_ping.h

@@ -0,0 +1,6 @@
+#ifndef CMD_ESPNOW_ECHO_PING_H
+#define CMD_ESPNOW_ECHO_PING_H
+
+void cmd_espnow_echo_ping_register(void);
+
+#endif

main/cmd/cmd_handler.c

@@ -57,6 +57,8 @@ static const char *message_type_name(uint16_t id) {
     return "TAP_NOTIFY";
   case alox_MessageType_CACHE_STATUS:
     return "CACHE_STATUS";
+  case alox_MessageType_ESPNOW_ECHO_PING:
+    return "ESPNOW_ECHO_PING";
   default:
     return "UNKNOWN";
   }

main/esp_now_comm.h

@@ -26,6 +26,17 @@ esp_err_t esp_now_comm_send_accel_deadzone(const uint8_t mac[CLIENT_MAC_LEN],
 esp_err_t esp_now_comm_send_unicast_test(const uint8_t mac[CLIENT_MAC_LEN],
                                          uint32_t seq);
 
+/** Result of a master-side ESP-NOW echo ping round-trip. */
+typedef struct {
+  uint64_t echoed_us;
+  uint32_t esp_rtt_us;
+} esp_now_echo_ping_result_t;
+
+/** Master: ESP-NOW echo ping round-trip; fills result on success. */
+esp_err_t esp_now_comm_echo_ping(const uint8_t mac[CLIENT_MAC_LEN],
+                                 uint64_t timestamp_us,
+                                 esp_now_echo_ping_result_t *result);
+
 /** Master: trigger find-me LED sequence on one slave. */
 esp_err_t esp_now_comm_send_find_me(const uint8_t mac[CLIENT_MAC_LEN],
                                     uint32_t client_id);

main/esp_now_core.c

@@ -21,7 +21,18 @@ static app_config_t s_config;
 static uint8_t s_wifi_channel;
 static uint8_t s_own_mac[ESP_NOW_ETH_ALEN];
 static SemaphoreHandle_t s_send_done;
+static SemaphoreHandle_t s_send_lock;
 static bool s_send_cb_ready;
+static volatile esp_now_send_status_t s_last_send_status;
+static volatile bool s_last_send_ok;
+
+#define ESPNOW_SEND_DONE_TIMEOUT_MS 500u
+#define ESPNOW_SEND_MAX_ATTEMPTS 8u
+#define ESPNOW_SEND_RETRY_DELAY_MS 10u
+#define ESPNOW_NOMEM_RETRY_DELAY_MS 50u
+
+#define ESPNOW_RELIABLE_MAX_ATTEMPTS 24u
+#define ESPNOW_RELIABLE_NOMEM_DELAY_MS 50u
 
 static uint8_t network_to_channel(uint8_t network) {
   if (network < 1 || network > 13) {
@@ -33,7 +44,8 @@ static uint8_t network_to_channel(uint8_t network) {
 static void espnow_send_done_cb(const esp_now_send_info_t *tx_info,
                                 esp_now_send_status_t status) {
   (void)tx_info;
-  (void)status;
+  s_last_send_status = status;
+  s_last_send_ok = (status == ESP_NOW_SEND_SUCCESS);
   if (s_send_done != NULL) {
     xSemaphoreGive(s_send_done);
   }
@@ -93,43 +105,140 @@ esp_err_t esp_now_core_ensure_broadcast_peer(void) {
   return esp_now_core_ensure_peer(ESPNOW_BCAST);
 }
 
+static esp_err_t send_with_backpressure(const uint8_t *dest_mac,
+                                        const alox_EspNowMessage *msg,
+                                        uint32_t max_attempts,
+                                        uint32_t nomem_delay_ms,
+                                        uint32_t retry_delay_ms,
+                                        bool quiet_retries) {
+  if (s_send_lock == NULL ||
+      xSemaphoreTake(s_send_lock, pdMS_TO_TICKS(5000)) != pdTRUE) {
+    return ESP_ERR_TIMEOUT;
+  }
+
+  uint8_t buf[ESPNOW_PB_MAX_SIZE];
+  size_t len = 0;
+  esp_err_t result = ESP_FAIL;
+
+  esp_err_t err = esp_now_proto_encode(msg, buf, sizeof(buf), &len);
+  if (err != ESP_OK) {
+    ESP_LOGW(TAG, "encode failed");
+    result = err;
+    goto out;
+  }
+
+  if (len > ESP_NOW_MAX_DATA_LEN) {
+    ESP_LOGW(TAG, "encoded len %u > ESP-NOW max %u", (unsigned)len,
+             (unsigned)ESP_NOW_MAX_DATA_LEN);
+    result = ESP_ERR_INVALID_SIZE;
+    goto out;
+  }
+
+  if (esp_now_core_ensure_peer(dest_mac) != ESP_OK) {
+    result = ESP_FAIL;
+    goto out;
+  }
+
+  for (uint32_t attempt = 0; attempt < max_attempts; attempt++) {
+    if (s_send_cb_ready && s_send_done != NULL) {
+      xSemaphoreTake(s_send_done, 0);
+    }
+    s_last_send_ok = false;
+
+    err = esp_now_send(dest_mac, buf, len);
+    if (err != ESP_OK) {
+      const bool last = (attempt + 1 >= max_attempts);
+      if (!quiet_retries || last) {
+        ESP_LOGW(TAG, "send type=%u failed (attempt %lu/%lu): %s",
+                 (unsigned)msg->type, (unsigned long)(attempt + 1),
+                 (unsigned long)max_attempts, esp_err_to_name(err));
+      }
+      vTaskDelay(pdMS_TO_TICKS(err == ESP_ERR_ESPNOW_NO_MEM ? nomem_delay_ms
+                                                             : retry_delay_ms));
+      continue;
+    }
+
+    if (s_send_cb_ready && s_send_done != NULL) {
+      if (xSemaphoreTake(s_send_done, pdMS_TO_TICKS(ESPNOW_SEND_DONE_TIMEOUT_MS)) !=
+          pdTRUE) {
+        const bool last = (attempt + 1 >= max_attempts);
+        if (!quiet_retries || last) {
+          ESP_LOGW(TAG, "send type=%u done timeout (attempt %lu/%lu)",
+                   (unsigned)msg->type, (unsigned long)(attempt + 1),
+                   (unsigned long)max_attempts);
+        }
+        vTaskDelay(pdMS_TO_TICKS(retry_delay_ms));
+        continue;
+      }
+      if (!s_last_send_ok) {
+        const bool last = (attempt + 1 >= max_attempts);
+        if (!quiet_retries || last) {
+          ESP_LOGW(TAG, "send type=%u peer status=%d (attempt %lu/%lu)",
+                   (unsigned)msg->type, (int)s_last_send_status,
+                   (unsigned long)(attempt + 1), (unsigned long)max_attempts);
+        }
+        vTaskDelay(pdMS_TO_TICKS(retry_delay_ms));
+        continue;
+      }
+    }
+    result = ESP_OK;
+    goto out;
+  }
+
+out:
+  xSemaphoreGive(s_send_lock);
+  return result;
+}
+
 esp_err_t esp_now_core_send_wait(const uint8_t *dest_mac,
                                  const alox_EspNowMessage *msg) {
+  return send_with_backpressure(dest_mac, msg, ESPNOW_SEND_MAX_ATTEMPTS,
+                                ESPNOW_NOMEM_RETRY_DELAY_MS,
+                                ESPNOW_SEND_RETRY_DELAY_MS, false);
+}
+
+esp_err_t esp_now_core_send_reliable(const uint8_t *dest_mac,
+                                     const alox_EspNowMessage *msg) {
+  return send_with_backpressure(dest_mac, msg, ESPNOW_RELIABLE_MAX_ATTEMPTS,
+                                ESPNOW_RELIABLE_NOMEM_DELAY_MS,
+                                ESPNOW_SEND_RETRY_DELAY_MS, true);
+}
+
+esp_err_t esp_now_core_send_fast(const uint8_t *dest_mac,
+                                 const alox_EspNowMessage *msg) {
+  if (s_send_lock == NULL ||
+      xSemaphoreTake(s_send_lock, pdMS_TO_TICKS(5000)) != pdTRUE) {
+    return ESP_ERR_TIMEOUT;
+  }
+
   uint8_t buf[ESPNOW_PB_MAX_SIZE];
   size_t len = 0;
 
   esp_err_t err = esp_now_proto_encode(msg, buf, sizeof(buf), &len);
   if (err != ESP_OK) {
     ESP_LOGW(TAG, "encode failed");
+    xSemaphoreGive(s_send_lock);
     return err;
   }
 
   if (len > ESP_NOW_MAX_DATA_LEN) {
     ESP_LOGW(TAG, "encoded len %u > ESP-NOW max %u", (unsigned)len,
              (unsigned)ESP_NOW_MAX_DATA_LEN);
+    xSemaphoreGive(s_send_lock);
     return ESP_ERR_INVALID_SIZE;
   }
 
   if (esp_now_core_ensure_peer(dest_mac) != ESP_OK) {
+    xSemaphoreGive(s_send_lock);
     return ESP_FAIL;
   }
 
-  if (s_send_cb_ready && s_send_done != NULL) {
-    xSemaphoreTake(s_send_done, 0);
-  }
-
   err = esp_now_send(dest_mac, buf, len);
   if (err != ESP_OK) {
     ESP_LOGW(TAG, "send type=%u failed: %s", (unsigned)msg->type,
              esp_err_to_name(err));
-    return err;
-  }
-
-  if (s_send_cb_ready && s_send_done != NULL) {
-    if (xSemaphoreTake(s_send_done, pdMS_TO_TICKS(50)) != pdTRUE) {
-      ESP_LOGW(TAG, "send type=%u done timeout", (unsigned)msg->type);
-    }
   }
+  xSemaphoreGive(s_send_lock);
   return err;
 }
 
@@ -163,7 +272,8 @@ esp_err_t esp_now_core_init_radio(uint8_t channel) {
 
 void esp_now_core_init_send_done(void) {
   s_send_done = xSemaphoreCreateBinary();
-  if (s_send_done != NULL &&
+  s_send_lock = xSemaphoreCreateMutex();
+  if (s_send_done != NULL && s_send_lock != NULL &&
       esp_now_register_send_cb(espnow_send_done_cb) == ESP_OK) {
     s_send_cb_ready = true;
   } else {

main/esp_now_master.c

@@ -5,8 +5,10 @@
 #include "esp_now_proto.h"
 #include "board_input.h"
 #include "ota_espnow.h"
+#include "ota_session.h"
 #include "ota_uart.h"
 #include "esp_log.h"
+#include "esp_timer.h"
 #include "freertos/FreeRTOS.h"
 #include "freertos/idf_additions.h"
 #include <string.h>
@@ -51,6 +53,66 @@ static esp_err_t send_unicast_test(const uint8_t *dest_mac, uint32_t seq) {
   return esp_now_core_send(dest_mac, &msg);
 }
 
+#define ESPNOW_ECHO_PING_TIMEOUT_MS 500
+#define ECHO_PING_TAG "[ECHO_PING]"
+
+static SemaphoreHandle_t s_echo_pong_sem;
+static bool s_echo_waiting;
+static uint64_t s_echo_expect_ts;
+static uint32_t s_echo_esp_rtt_us;
+static uint8_t s_echo_expect_mac[ESP_NOW_ETH_ALEN];
+
+static esp_err_t echo_ping_init(void) {
+  if (s_echo_pong_sem != NULL) {
+    return ESP_OK;
+  }
+  s_echo_pong_sem = xSemaphoreCreateBinary();
+  if (s_echo_pong_sem == NULL) {
+    return ESP_ERR_NO_MEM;
+  }
+  return ESP_OK;
+}
+
+static esp_err_t send_echo_ping(const uint8_t *dest_mac, uint64_t host_timestamp_us,
+                                uint64_t master_time_us) {
+  alox_EspNowMessage msg = alox_EspNowMessage_init_zero;
+  msg.type = alox_EspNowMessageType_ESPNOW_ECHO_PING;
+  msg.which_payload = alox_EspNowMessage_echo_ping_tag;
+  msg.payload.echo_ping.host_timestamp_us = host_timestamp_us;
+  msg.payload.echo_ping.master_time_us = master_time_us;
+  char mac_str[18];
+  esp_now_core_mac_to_str(dest_mac, mac_str, sizeof(mac_str));
+  ESP_LOGI(ECHO_PING_TAG, "ESP-NOW PING send to %s host_ts=%llu master_time_us=%llu",
+           mac_str, (unsigned long long)host_timestamp_us,
+           (unsigned long long)master_time_us);
+  return esp_now_core_send_fast(dest_mac, &msg);
+}
+
+static void echo_ping_on_pong(const uint8_t mac[ESP_NOW_ETH_ALEN],
+                              const alox_EspNowEchoPong *pong) {
+  if (pong == NULL || !s_echo_waiting) {
+    return;
+  }
+  if (!esp_now_core_mac_equal(mac, s_echo_expect_mac)) {
+    return;
+  }
+  if (pong->host_timestamp_us != s_echo_expect_ts) {
+    return;
+  }
+  int64_t now_us = esp_timer_get_time();
+  s_echo_esp_rtt_us =
+      (uint32_t)(now_us - (int64_t)pong->master_time_us);
+  char mac_str[18];
+  esp_now_core_mac_to_str(mac, mac_str, sizeof(mac_str));
+  ESP_LOGI(ECHO_PING_TAG,
+           "ESP-NOW PONG recv from %s host_ts=%llu master_time_us=%llu "
+           "recv_time_us=%lld esp_rtt_us=%lu",
+           mac_str, (unsigned long long)pong->host_timestamp_us,
+           (unsigned long long)pong->master_time_us, (long long)now_us,
+           (unsigned long)s_echo_esp_rtt_us);
+  xSemaphoreGive(s_echo_pong_sem);
+}
+
 static esp_err_t send_find_me(const uint8_t *dest_mac, uint32_t client_id) {
   alox_EspNowMessage msg = alox_EspNowMessage_init_zero;
   msg.type = alox_EspNowMessageType_ESPNOW_FIND_ME;
@@ -119,7 +181,7 @@ static esp_err_t send_ota_payload(const uint8_t *dest_mac, uint32_t seq,
   msg.payload.ota_payload.seq = seq;
   msg.payload.ota_payload.data.size = len;
   memcpy(msg.payload.ota_payload.data.bytes, data, len);
-  return esp_now_core_send_wait(dest_mac, &msg);
+  return esp_now_core_send_reliable(dest_mac, &msg);
 }
 
 static esp_err_t send_ota_end(const uint8_t *dest_mac) {
@@ -224,6 +286,48 @@ esp_err_t esp_now_comm_send_unicast_test(const uint8_t mac[CLIENT_MAC_LEN],
   return err;
 }
 
+esp_err_t esp_now_comm_echo_ping(const uint8_t mac[CLIENT_MAC_LEN],
+                                 uint64_t timestamp_us,
+                                 esp_now_echo_ping_result_t *result) {
+  if (mac == NULL || !esp_now_core_is_master()) {
+    return ESP_ERR_INVALID_STATE;
+  }
+  if (echo_ping_init() != ESP_OK) {
+    return ESP_ERR_NO_MEM;
+  }
+
+  xSemaphoreTake(s_echo_pong_sem, 0);
+  s_echo_waiting = true;
+  s_echo_expect_ts = timestamp_us;
+  s_echo_esp_rtt_us = 0;
+  memcpy(s_echo_expect_mac, mac, ESP_NOW_ETH_ALEN);
+
+  uint64_t master_time_us = (uint64_t)esp_timer_get_time();
+  esp_err_t err = send_echo_ping(mac, timestamp_us, master_time_us);
+  if (err != ESP_OK) {
+    s_echo_waiting = false;
+    return err;
+  }
+
+  if (xSemaphoreTake(s_echo_pong_sem,
+                     pdMS_TO_TICKS(ESPNOW_ECHO_PING_TIMEOUT_MS)) != pdTRUE) {
+    s_echo_waiting = false;
+    char mac_str[18];
+    esp_now_core_mac_to_str(mac, mac_str, sizeof(mac_str));
+    ESP_LOGW(ECHO_PING_TAG,
+             "ESP-NOW PONG timeout to %s host_ts=%llu",
+             mac_str, (unsigned long long)timestamp_us);
+    return ESP_ERR_TIMEOUT;
+  }
+
+  s_echo_waiting = false;
+  if (result != NULL) {
+    result->echoed_us = timestamp_us;
+    result->esp_rtt_us = s_echo_esp_rtt_us;
+  }
+  return ESP_OK;
+}
+
 esp_err_t esp_now_comm_send_accel_stream(const uint8_t mac[CLIENT_MAC_LEN],
                                          uint32_t client_id, bool enable) {
   if (mac == NULL || !esp_now_core_is_master()) {
@@ -415,6 +519,12 @@ void esp_now_master_on_recv(const esp_now_recv_info_t *info, const uint8_t *data
     return;
   }
 
+  if (msg.which_payload == alox_EspNowMessage_echo_pong_tag) {
+    esp_now_core_ensure_peer(info->src_addr);
+    echo_ping_on_pong(info->src_addr, &msg.payload.echo_pong);
+    return;
+  }
+
   if (msg.type == alox_EspNowMessageType_ESPNOW_BATTERY_REPORT &&
       msg.which_payload != alox_EspNowMessage_battery_report_tag) {
     ESP_LOGW(TAG, "BATTERY_REPORT type but which=%u", msg.which_payload);
@@ -439,7 +549,10 @@ static void discover_task(void *param) {
            (unsigned)esp_now_core_wifi_channel());
 
   while (1) {
-    esp_now_core_send(ESPNOW_BCAST, &msg);
+    msg.payload.discover.master_ota_pending = ota_session_busy();
+    if (!ota_espnow_distribution_active()) {
+      esp_now_core_send_fast(ESPNOW_BCAST, &msg);
+    }
     vTaskDelay(pdMS_TO_TICKS(ESPNOW_DISCOVER_INTERVAL_MS));
   }
 }

main/esp_now_slave.c

@@ -21,6 +21,8 @@
 
 #define ESPNOW_HEARTBEAT_INTERVAL_MS 1000
 #define SLAVE_MASTER_LOST_MS (ESPNOW_HEARTBEAT_INTERVAL_MS * 5)
+/** While master or slave OTA is in progress (discover may be sparse). */
+#define SLAVE_MASTER_OTA_GRACE_MS 300000u
 #define ESPNOW_ACCEL_INTERVAL_MS 16
 #define ESPNOW_BATTERY_INTERVAL_MS 30000
 #define SLAVE_BATTERY_AFTER_JOIN_MS 150
@@ -28,6 +30,7 @@
 static const char *TAG = "[ESPNOW_S]";
 
 static bool s_joined;
+static bool s_master_ota_grace;
 static bool s_accel_stream_enabled;
 static bool s_tap_notify_single;
 static bool s_tap_notify_double;
@@ -106,8 +109,18 @@ static esp_err_t send_battery_report(const uint8_t *dest_mac,
   return esp_now_core_send(dest_mac, &msg);
 }
 
+static uint32_t slave_master_lost_ms(void) {
+  if (ota_uart_is_active() || s_master_ota_grace) {
+    return SLAVE_MASTER_OTA_GRACE_MS;
+  }
+  return SLAVE_MASTER_LOST_MS;
+}
+
+static void touch_master_presence(uint32_t now) { s_last_discover_ms = now; }
+
 static void reset_join(void) {
   s_joined = false;
+  s_master_ota_grace = false;
   s_accel_stream_enabled = false;
   memset(s_master_mac, 0, sizeof(s_master_mac));
   s_last_discover_ms = 0;
@@ -216,6 +229,36 @@ static void handle_unicast_test(const uint8_t *master_mac,
            (unsigned long)test->seq, (int)s_joined);
 }
 
+static void handle_echo_ping(const uint8_t *master_mac,
+                             const alox_EspNowEchoPing *ping) {
+  if (ping == NULL || !s_joined ||
+      !esp_now_core_mac_equal(master_mac, s_master_mac)) {
+    return;
+  }
+
+  char mac_str[18];
+  esp_now_core_mac_to_str(master_mac, mac_str, sizeof(mac_str));
+  ESP_LOGI(TAG, "ESP-NOW PING recv from %s host_ts=%llu master_time_us=%llu",
+           mac_str, (unsigned long long)ping->host_timestamp_us,
+           (unsigned long long)ping->master_time_us);
+
+  alox_EspNowMessage msg = alox_EspNowMessage_init_zero;
+  msg.type = alox_EspNowMessageType_ESPNOW_ECHO_PONG;
+  msg.which_payload = alox_EspNowMessage_echo_pong_tag;
+  msg.payload.echo_pong.host_timestamp_us = ping->host_timestamp_us;
+  msg.payload.echo_pong.master_time_us = ping->master_time_us;
+
+  esp_err_t err = esp_now_core_send_fast(s_master_mac, &msg);
+  if (err != ESP_OK) {
+    ESP_LOGW(TAG, "ECHO PONG send failed: %s", esp_err_to_name(err));
+    return;
+  }
+
+  ESP_LOGI(TAG, "ESP-NOW PONG send to %s host_ts=%llu master_time_us=%llu",
+           mac_str, (unsigned long long)ping->host_timestamp_us,
+           (unsigned long long)ping->master_time_us);
+}
+
 static void handle_restart(const uint8_t *master_mac,
                            const alox_EspNowRestart *req) {
   const uint8_t *own = esp_now_core_own_mac();
@@ -358,8 +401,13 @@ static void handle_discover(const uint8_t *sender_mac,
     if (!esp_now_core_mac_equal(sender_mac, s_master_mac)) {
       return;
     }
-    if ((now - s_last_discover_ms) <= SLAVE_MASTER_LOST_MS) {
+    s_master_ota_grace = discover->master_ota_pending;
-      s_last_discover_ms = now;
+    if ((now - s_last_discover_ms) <= slave_master_lost_ms()) {
+      touch_master_presence(now);
+      return;
+    }
+    if (ota_uart_is_active()) {
+      touch_master_presence(now);
       return;
     }
     ESP_LOGW(TAG, "master lost, rejoining");
@@ -368,7 +416,8 @@ static void handle_discover(const uint8_t *sender_mac,
 
   memcpy(s_master_mac, sender_mac, ESP_NOW_ETH_ALEN);
   s_joined = true;
-  s_last_discover_ms = now;
+  s_master_ota_grace = discover->master_ota_pending;
+  touch_master_presence(now);
   esp_now_core_ensure_peer(sender_mac);
 
   char mac_str[18];
@@ -384,10 +433,14 @@ static void check_master_timeout(void) {
   if (!s_joined || s_last_discover_ms == 0) {
     return;
   }
+  if (ota_uart_is_active()) {
+    return;
+  }
   uint32_t now = esp_now_core_now_ms();
-  if ((now - s_last_discover_ms) > SLAVE_MASTER_LOST_MS) {
+  uint32_t limit = slave_master_lost_ms();
-    ESP_LOGW(TAG, "no master discover for %u ms, reconnecting",
+  if ((now - s_last_discover_ms) > limit) {
-             (unsigned)(now - s_last_discover_ms));
+    ESP_LOGW(TAG, "no master discover for %u ms (limit %u), reconnecting",
+             (unsigned)(now - s_last_discover_ms), (unsigned)limit);
     reset_join();
   }
 }
@@ -481,12 +534,16 @@ void esp_now_slave_on_recv(const esp_now_recv_info_t *info, const uint8_t *data,
 
   if (ota_uart_is_active()) {
     switch (msg.which_payload) {
+    case alox_EspNowMessage_discover_tag:
+      handle_discover(info->src_addr, &msg.payload.discover);
+      break;
     case alox_EspNowMessage_ota_start_tag:
     case alox_EspNowMessage_ota_payload_tag:
     case alox_EspNowMessage_ota_end_tag:
       if (!from_joined_master(info->src_addr)) {
         break;
       }
+      touch_master_presence(esp_now_core_now_ms());
       if (msg.which_payload == alox_EspNowMessage_ota_start_tag) {
         ota_espnow_slave_on_start(info->src_addr, &msg.payload.ota_start);
       } else if (msg.which_payload == alox_EspNowMessage_ota_payload_tag) {
@@ -510,6 +567,11 @@ void esp_now_slave_on_recv(const esp_now_recv_info_t *info, const uint8_t *data,
       handle_unicast_test(info->src_addr, &msg.payload.unicast_test);
     }
     break;
+  case alox_EspNowMessage_echo_ping_tag:
+    if (from_joined_master(info->src_addr)) {
+      handle_echo_ping(info->src_addr, &msg.payload.echo_ping);
+    }
+    break;
   case alox_EspNowMessage_accel_deadzone_tag:
     if (from_joined_master(info->src_addr)) {
       handle_accel_deadzone(info->src_addr, &msg.payload.accel_deadzone);
@@ -545,6 +607,11 @@ void esp_now_slave_on_recv(const esp_now_recv_info_t *info, const uint8_t *data,
       handle_restart(info->src_addr, &msg.payload.restart);
     }
     break;
+  case alox_EspNowMessage_ota_start_tag:
+    if (from_joined_master(info->src_addr)) {
+      ota_espnow_slave_on_start(info->src_addr, &msg.payload.ota_start);
+    }
+    break;
   default:
     ESP_LOGW(TAG, "unhandled which=%u type=%u", msg.which_payload,
              (unsigned)msg.type);

main/led_ring.c

@@ -158,7 +158,7 @@ void led_ring_init(void) {
 
 void led_ring_send_command(led_command_t *cmd) {
   if (led_queue != NULL) {
-    xQueueSend(led_queue, cmd, portMAX_DELAY);
+    (void)xQueueSend(led_queue, cmd, 0);
   }
 }
 

main/powerpod.c

@@ -5,6 +5,7 @@
 #include "cmd_tap_notify.h"
 #include "cmd_cache_status.h"
 #include "cmd_espnow_unicast_test.h"
+#include "cmd_espnow_echo_ping.h"
 #include "cmd_espnow_find_me.h"
 #include "cmd_restart.h"
 #include "cmd_client_info.h"
@@ -72,6 +73,9 @@ uint8_t reverse_high_nibble_lut(uint8_t n) {
 }
 
 void app_main(void) {
+
+  esp_log_level_set("*", ESP_LOG_NONE);
+
   if (pod_settings_init() != ESP_OK) {
     ESP_LOGW(TAG, "settings NVS init failed; using defaults");
   }
@@ -185,6 +189,7 @@ void app_main(void) {
     cmd_tap_notify_register();
     cmd_cache_status_register();
     cmd_espnow_unicast_test_register();
+    cmd_espnow_echo_ping_register();
     cmd_espnow_find_me_register();
     cmd_restart_register();
     cmd_led_ring_register();

main/proto/esp_now_messages.pb.c

@@ -9,6 +9,12 @@
 PB_BIND(alox_EspNowUnicastTest, alox_EspNowUnicastTest, AUTO)
 
 
+PB_BIND(alox_EspNowEchoPing, alox_EspNowEchoPing, AUTO)
+
+
+PB_BIND(alox_EspNowEchoPong, alox_EspNowEchoPong, AUTO)
+
+
 PB_BIND(alox_EspNowFindMe, alox_EspNowFindMe, AUTO)
 
 

main/proto/esp_now_messages.pb.h

@@ -29,7 +29,9 @@ typedef enum _alox_EspNowMessageType {
     alox_EspNowMessageType_ESPNOW_BATTERY_QUERY = 15,
     alox_EspNowMessageType_ESPNOW_BATTERY_REPORT = 16,
     alox_EspNowMessageType_ESPNOW_SET_TAP_NOTIFY = 17,
-    alox_EspNowMessageType_ESPNOW_TAP_EVENT = 18
+    alox_EspNowMessageType_ESPNOW_TAP_EVENT = 18,
+    alox_EspNowMessageType_ESPNOW_ECHO_PING = 19,
+    alox_EspNowMessageType_ESPNOW_ECHO_PONG = 20
 } alox_EspNowMessageType;
 
 /* Struct definitions */
@@ -37,6 +39,19 @@ typedef struct _alox_EspNowUnicastTest {
     uint32_t seq;
 } alox_EspNowUnicastTest;
 
+/* * Master → slave: echo ping (host ts + master monotonic time for RTT). */
+typedef struct _alox_EspNowEchoPing {
+    uint64_t host_timestamp_us;
+    /* * esp_timer_get_time() (µs since boot) when master forwarded this message. */
+    uint64_t master_time_us;
+} alox_EspNowEchoPing;
+
+/* * Slave → master: echo ping payload unchanged. */
+typedef struct _alox_EspNowEchoPong {
+    uint64_t host_timestamp_us;
+    uint64_t master_time_us;
+} alox_EspNowEchoPong;
+
 /* * Master → slave: locate pod (LED ring R/G/B ×3 @ full brightness). */
 typedef struct _alox_EspNowFindMe {
     /* * 0 = any slave; otherwise only slave_id must match */
@@ -50,6 +65,8 @@ typedef struct _alox_EspNowRestart {
 
 typedef struct _alox_EspNowDiscover {
     uint32_t network;
+    /* * Master is in an OTA session (UART upload or ESP-NOW distribution). */
+    bool master_ota_pending;
 } alox_EspNowDiscover;
 
 typedef struct _alox_EspNowSlavePresence {
@@ -169,6 +186,8 @@ typedef struct _alox_EspNowMessage {
         alox_EspNowBatteryReport battery_report;
         alox_EspNowTapNotify tap_notify;
         alox_EspNowTapEvent tap_event;
+        alox_EspNowEchoPing echo_ping;
+        alox_EspNowEchoPong echo_pong;
     } payload;
 } alox_EspNowMessage;
 
@@ -179,8 +198,10 @@ extern "C" {
 
 /* Helper constants for enums */
 #define _alox_EspNowMessageType_MIN alox_EspNowMessageType_ESPNOW_UNKNOWN
-#define _alox_EspNowMessageType_MAX alox_EspNowMessageType_ESPNOW_TAP_EVENT
+#define _alox_EspNowMessageType_MAX alox_EspNowMessageType_ESPNOW_ECHO_PONG
-#define _alox_EspNowMessageType_ARRAYSIZE ((alox_EspNowMessageType)(alox_EspNowMessageType_ESPNOW_TAP_EVENT+1))
+#define _alox_EspNowMessageType_ARRAYSIZE ((alox_EspNowMessageType)(alox_EspNowMessageType_ESPNOW_ECHO_PONG+1))
+
+
 
 
 
@@ -204,9 +225,11 @@ extern "C" {
 
 /* Initializer values for message structs */
 #define alox_EspNowUnicastTest_init_default      {0}
+#define alox_EspNowEchoPing_init_default         {0, 0}
+#define alox_EspNowEchoPong_init_default         {0, 0}
 #define alox_EspNowFindMe_init_default           {0}
 #define alox_EspNowRestart_init_default          {0}
-#define alox_EspNowDiscover_init_default         {0}
+#define alox_EspNowDiscover_init_default         {0, 0}
 #define alox_EspNowSlavePresence_init_default    {0, {{NULL}, NULL}, 0, 0, 0, 0}
 #define alox_EspNowAccelDeadzone_init_default    {0, 0}
 #define alox_EspNowAccelStream_init_default      {0, 0}
@@ -222,9 +245,11 @@ extern "C" {
 #define alox_EspNowOtaStatus_init_default        {0, 0, 0}
 #define alox_EspNowMessage_init_default          {_alox_EspNowMessageType_MIN, 0, {alox_EspNowDiscover_init_default}}
 #define alox_EspNowUnicastTest_init_zero         {0}
+#define alox_EspNowEchoPing_init_zero            {0, 0}
+#define alox_EspNowEchoPong_init_zero            {0, 0}
 #define alox_EspNowFindMe_init_zero              {0}
 #define alox_EspNowRestart_init_zero             {0}
-#define alox_EspNowDiscover_init_zero            {0}
+#define alox_EspNowDiscover_init_zero            {0, 0}
 #define alox_EspNowSlavePresence_init_zero       {0, {{NULL}, NULL}, 0, 0, 0, 0}
 #define alox_EspNowAccelDeadzone_init_zero       {0, 0}
 #define alox_EspNowAccelStream_init_zero         {0, 0}
@@ -242,9 +267,14 @@ extern "C" {
 
 /* Field tags (for use in manual encoding/decoding) */
 #define alox_EspNowUnicastTest_seq_tag           1
+#define alox_EspNowEchoPing_host_timestamp_us_tag 1
+#define alox_EspNowEchoPing_master_time_us_tag   2
+#define alox_EspNowEchoPong_host_timestamp_us_tag 1
+#define alox_EspNowEchoPong_master_time_us_tag   2
 #define alox_EspNowFindMe_client_id_tag          1
 #define alox_EspNowRestart_client_id_tag         1
 #define alox_EspNowDiscover_network_tag          1
+#define alox_EspNowDiscover_master_ota_pending_tag 2
 #define alox_EspNowSlavePresence_network_tag     1
 #define alox_EspNowSlavePresence_mac_tag         2
 #define alox_EspNowSlavePresence_version_tag     3
@@ -306,6 +336,8 @@ extern "C" {
 #define alox_EspNowMessage_battery_report_tag    17
 #define alox_EspNowMessage_tap_notify_tag        18
 #define alox_EspNowMessage_tap_event_tag         19
+#define alox_EspNowMessage_echo_ping_tag         20
+#define alox_EspNowMessage_echo_pong_tag         21
 
 /* Struct field encoding specification for nanopb */
 #define alox_EspNowUnicastTest_FIELDLIST(X, a) \
@@ -313,6 +345,18 @@ X(a, STATIC,   SINGULAR, UINT32,   seq,               1)
 #define alox_EspNowUnicastTest_CALLBACK NULL
 #define alox_EspNowUnicastTest_DEFAULT NULL
 
+#define alox_EspNowEchoPing_FIELDLIST(X, a) \
+X(a, STATIC,   SINGULAR, UINT64,   host_timestamp_us,   1) \
+X(a, STATIC,   SINGULAR, UINT64,   master_time_us,    2)
+#define alox_EspNowEchoPing_CALLBACK NULL
+#define alox_EspNowEchoPing_DEFAULT NULL
+
+#define alox_EspNowEchoPong_FIELDLIST(X, a) \
+X(a, STATIC,   SINGULAR, UINT64,   host_timestamp_us,   1) \
+X(a, STATIC,   SINGULAR, UINT64,   master_time_us,    2)
+#define alox_EspNowEchoPong_CALLBACK NULL
+#define alox_EspNowEchoPong_DEFAULT NULL
+
 #define alox_EspNowFindMe_FIELDLIST(X, a) \
 X(a, STATIC,   SINGULAR, UINT32,   client_id,         1)
 #define alox_EspNowFindMe_CALLBACK NULL
@@ -324,7 +368,8 @@ X(a, STATIC,   SINGULAR, UINT32,   client_id,         1)
 #define alox_EspNowRestart_DEFAULT NULL
 
 #define alox_EspNowDiscover_FIELDLIST(X, a) \
-X(a, STATIC,   SINGULAR, UINT32,   network,           1)
+X(a, STATIC,   SINGULAR, UINT32,   network,           1) \
+X(a, STATIC,   SINGULAR, BOOL,     master_ota_pending,   2)
 #define alox_EspNowDiscover_CALLBACK NULL
 #define alox_EspNowDiscover_DEFAULT NULL
 
@@ -442,7 +487,9 @@ X(a, STATIC,   ONEOF,    MESSAGE,  (payload,led_ring,payload.led_ring),  15) \
 X(a, STATIC,   ONEOF,    MESSAGE,  (payload,battery_query,payload.battery_query),  16) \
 X(a, STATIC,   ONEOF,    MESSAGE,  (payload,battery_report,payload.battery_report),  17) \
 X(a, STATIC,   ONEOF,    MESSAGE,  (payload,tap_notify,payload.tap_notify),  18) \
-X(a, STATIC,   ONEOF,    MESSAGE,  (payload,tap_event,payload.tap_event),  19)
+X(a, STATIC,   ONEOF,    MESSAGE,  (payload,tap_event,payload.tap_event),  19) \
+X(a, STATIC,   ONEOF,    MESSAGE,  (payload,echo_ping,payload.echo_ping),  20) \
+X(a, STATIC,   ONEOF,    MESSAGE,  (payload,echo_pong,payload.echo_pong),  21)
 #define alox_EspNowMessage_CALLBACK NULL
 #define alox_EspNowMessage_DEFAULT NULL
 #define alox_EspNowMessage_payload_discover_MSGTYPE alox_EspNowDiscover
@@ -463,8 +510,12 @@ X(a, STATIC,   ONEOF,    MESSAGE,  (payload,tap_event,payload.tap_event),  19)
 #define alox_EspNowMessage_payload_battery_report_MSGTYPE alox_EspNowBatteryReport
 #define alox_EspNowMessage_payload_tap_notify_MSGTYPE alox_EspNowTapNotify
 #define alox_EspNowMessage_payload_tap_event_MSGTYPE alox_EspNowTapEvent
+#define alox_EspNowMessage_payload_echo_ping_MSGTYPE alox_EspNowEchoPing
+#define alox_EspNowMessage_payload_echo_pong_MSGTYPE alox_EspNowEchoPong
 
 extern const pb_msgdesc_t alox_EspNowUnicastTest_msg;
+extern const pb_msgdesc_t alox_EspNowEchoPing_msg;
+extern const pb_msgdesc_t alox_EspNowEchoPong_msg;
 extern const pb_msgdesc_t alox_EspNowFindMe_msg;
 extern const pb_msgdesc_t alox_EspNowRestart_msg;
 extern const pb_msgdesc_t alox_EspNowDiscover_msg;
@@ -485,6 +536,8 @@ extern const pb_msgdesc_t alox_EspNowMessage_msg;
 
 /* Defines for backwards compatibility with code written before nanopb-0.4.0 */
 #define alox_EspNowUnicastTest_fields &alox_EspNowUnicastTest_msg
+#define alox_EspNowEchoPing_fields &alox_EspNowEchoPing_msg
+#define alox_EspNowEchoPong_fields &alox_EspNowEchoPong_msg
 #define alox_EspNowFindMe_fields &alox_EspNowFindMe_msg
 #define alox_EspNowRestart_fields &alox_EspNowRestart_msg
 #define alox_EspNowDiscover_fields &alox_EspNowDiscover_msg
@@ -512,7 +565,9 @@ extern const pb_msgdesc_t alox_EspNowMessage_msg;
 #define alox_EspNowAccelStream_size              8
 #define alox_EspNowBatteryQuery_size             6
 #define alox_EspNowBatteryReport_size            22
-#define alox_EspNowDiscover_size                 6
+#define alox_EspNowDiscover_size                 8
+#define alox_EspNowEchoPing_size                 22
+#define alox_EspNowEchoPong_size                 22
 #define alox_EspNowFindMe_size                   6
 #define alox_EspNowLedRing_size                  60
 #define alox_EspNowOtaEnd_size                   0

main/proto/esp_now_messages.proto

@@ -24,12 +24,27 @@ enum EspNowMessageType {
   ESPNOW_BATTERY_REPORT = 16;
   ESPNOW_SET_TAP_NOTIFY = 17;
   ESPNOW_TAP_EVENT = 18;
+  ESPNOW_ECHO_PING = 19;
+  ESPNOW_ECHO_PONG = 20;
 }
 
 message EspNowUnicastTest {
   uint32 seq = 1;
 }
 
+/** Master → slave: echo ping (host ts + master monotonic time for RTT). */
+message EspNowEchoPing {
+  uint64 host_timestamp_us = 1;
+  /** esp_timer_get_time() (µs since boot) when master forwarded this message. */
+  uint64 master_time_us = 2;
+}
+
+/** Slave → master: echo ping payload unchanged. */
+message EspNowEchoPong {
+  uint64 host_timestamp_us = 1;
+  uint64 master_time_us = 2;
+}
+
 /** Master → slave: locate pod (LED ring R/G/B ×3 @ full brightness). */
 message EspNowFindMe {
   /** 0 = any slave; otherwise only slave_id must match */
@@ -43,6 +58,8 @@ message EspNowRestart {
 
 message EspNowDiscover {
   uint32 network = 1;
+  /** Master is in an OTA session (UART upload or ESP-NOW distribution). */
+  bool master_ota_pending = 2;
 }
 
 message EspNowSlavePresence {
@@ -158,5 +175,7 @@ message EspNowMessage {
     EspNowBatteryReport battery_report = 17;
     EspNowTapNotify tap_notify = 18;
     EspNowTapEvent tap_event = 19;
+    EspNowEchoPing echo_ping = 20;
+    EspNowEchoPong echo_pong = 21;
   }
 }

main/proto/uart_messages.pb.c

@@ -87,6 +87,12 @@ PB_BIND(alox_EspNowUnicastTestRequest, alox_EspNowUnicastTestRequest, AUTO)
 PB_BIND(alox_EspNowUnicastTestResponse, alox_EspNowUnicastTestResponse, AUTO)
 
 
+PB_BIND(alox_EspNowEchoPingRequest, alox_EspNowEchoPingRequest, AUTO)
+
+
+PB_BIND(alox_EspNowEchoPingResponse, alox_EspNowEchoPingResponse, AUTO)
+
+
 PB_BIND(alox_LedRingProgressRequest, alox_LedRingProgressRequest, AUTO)
 
 

main/proto/uart_messages.pb.h

@@ -32,7 +32,9 @@ typedef enum _alox_MessageType {
     alox_MessageType_BATTERY_STATUS = 26,
     alox_MessageType_TAP_NOTIFY = 27,
     /* * Combined cached accel + tap poll (one UART round-trip, ~16 ms cadence). */
-    alox_MessageType_CACHE_STATUS = 29
+    alox_MessageType_CACHE_STATUS = 29,
+    /* * Host → master → slave → master: timestamp echo round-trip (latency test). */
+    alox_MessageType_ESPNOW_ECHO_PING = 30
 } alox_MessageType;
 
 typedef enum _alox_TapKind {
@@ -235,6 +237,22 @@ typedef struct _alox_EspNowUnicastTestResponse {
     uint32_t seq;
 } alox_EspNowUnicastTestResponse;
 
+/* * Host → master: ESP-NOW echo ping to one slave (timestamp echoed back). */
+typedef struct _alox_EspNowEchoPingRequest {
+    uint32_t client_id;
+    /* * Microseconds since Unix epoch (host clock). */
+    uint64_t timestamp_us;
+} alox_EspNowEchoPingRequest;
+
+typedef struct _alox_EspNowEchoPingResponse {
+    bool success;
+    uint32_t client_id;
+    /* * Echoed host timestamp from goTool request. */
+    uint64_t timestamp_us;
+    /* * esp_timer_get_time() delta from ping send to pong recv (master→slave→master). */
+    uint32_t esp_rtt_us;
+} alox_EspNowEchoPingResponse;
+
 /* Host → master: LED ring on master (client_id=0) and/or slaves via ESP-NOW.
  mode: 0=clear, 1=progress (0–100 %), 2=digit (0–10), 3=blink, 4=find-me, 5=all LEDs solid color. */
 typedef struct _alox_LedRingProgressRequest {
@@ -371,6 +389,8 @@ typedef struct _alox_UartMessage {
         alox_TapNotifyResponse tap_notify_response;
         alox_CacheStatusRequest cache_status_request;
         alox_CacheStatusResponse cache_status_response;
+        alox_EspNowEchoPingRequest espnow_echo_ping_request;
+        alox_EspNowEchoPingResponse espnow_echo_ping_response;
     } payload;
 } alox_UartMessage;
 
@@ -381,8 +401,8 @@ extern "C" {
 
 /* Helper constants for enums */
 #define _alox_MessageType_MIN alox_MessageType_UNKNOWN
-#define _alox_MessageType_MAX alox_MessageType_CACHE_STATUS
+#define _alox_MessageType_MAX alox_MessageType_ESPNOW_ECHO_PING
-#define _alox_MessageType_ARRAYSIZE ((alox_MessageType)(alox_MessageType_CACHE_STATUS+1))
+#define _alox_MessageType_ARRAYSIZE ((alox_MessageType)(alox_MessageType_ESPNOW_ECHO_PING+1))
 
 #define _alox_TapKind_MIN alox_TapKind_TAP_NONE
 #define _alox_TapKind_MAX alox_TapKind_TAP_TRIPLE
@@ -431,6 +451,8 @@ extern "C" {
 
 
 
+
+
 
 /* Initializer values for message structs */
 #define alox_UartMessage_init_default            {_alox_MessageType_MIN, 0, {alox_Ack_init_default}}
@@ -460,6 +482,8 @@ extern "C" {
 #define alox_CacheStatusResponse_init_default    {0, {alox_CacheClientStatus_init_default, alox_CacheClientStatus_init_default, alox_CacheClientStatus_init_default, alox_CacheClientStatus_init_default, alox_CacheClientStatus_init_default, alox_CacheClientStatus_init_default, alox_CacheClientStatus_init_default, alox_CacheClientStatus_init_default, alox_CacheClientStatus_init_default, alox_CacheClientStatus_init_default, alox_CacheClientStatus_init_default, alox_CacheClientStatus_init_default, alox_CacheClientStatus_init_default, alox_CacheClientStatus_init_default, alox_CacheClientStatus_init_default, alox_CacheClientStatus_init_default}}
 #define alox_EspNowUnicastTestRequest_init_default {0, 0}
 #define alox_EspNowUnicastTestResponse_init_default {0, 0}
+#define alox_EspNowEchoPingRequest_init_default  {0, 0}
+#define alox_EspNowEchoPingResponse_init_default {0, 0, 0, 0}
 #define alox_LedRingProgressRequest_init_default {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}
 #define alox_LedRingProgressResponse_init_default {0, 0, 0, 0, 0, 0}
 #define alox_EspNowFindMeRequest_init_default    {0}
@@ -500,6 +524,8 @@ extern "C" {
 #define alox_CacheStatusResponse_init_zero       {0, {alox_CacheClientStatus_init_zero, alox_CacheClientStatus_init_zero, alox_CacheClientStatus_init_zero, alox_CacheClientStatus_init_zero, alox_CacheClientStatus_init_zero, alox_CacheClientStatus_init_zero, alox_CacheClientStatus_init_zero, alox_CacheClientStatus_init_zero, alox_CacheClientStatus_init_zero, alox_CacheClientStatus_init_zero, alox_CacheClientStatus_init_zero, alox_CacheClientStatus_init_zero, alox_CacheClientStatus_init_zero, alox_CacheClientStatus_init_zero, alox_CacheClientStatus_init_zero, alox_CacheClientStatus_init_zero}}
 #define alox_EspNowUnicastTestRequest_init_zero  {0, 0}
 #define alox_EspNowUnicastTestResponse_init_zero {0, 0}
+#define alox_EspNowEchoPingRequest_init_zero     {0, 0}
+#define alox_EspNowEchoPingResponse_init_zero    {0, 0, 0, 0}
 #define alox_LedRingProgressRequest_init_zero    {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}
 #define alox_LedRingProgressResponse_init_zero   {0, 0, 0, 0, 0, 0}
 #define alox_EspNowFindMeRequest_init_zero       {0}
@@ -599,6 +625,12 @@ extern "C" {
 #define alox_EspNowUnicastTestRequest_seq_tag    2
 #define alox_EspNowUnicastTestResponse_success_tag 1
 #define alox_EspNowUnicastTestResponse_seq_tag   2
+#define alox_EspNowEchoPingRequest_client_id_tag 1
+#define alox_EspNowEchoPingRequest_timestamp_us_tag 2
+#define alox_EspNowEchoPingResponse_success_tag  1
+#define alox_EspNowEchoPingResponse_client_id_tag 2
+#define alox_EspNowEchoPingResponse_timestamp_us_tag 3
+#define alox_EspNowEchoPingResponse_esp_rtt_us_tag 4
 #define alox_LedRingProgressRequest_mode_tag     1
 #define alox_LedRingProgressRequest_progress_tag 2
 #define alox_LedRingProgressRequest_digit_tag    3
@@ -671,6 +703,8 @@ extern "C" {
 #define alox_UartMessage_tap_notify_response_tag 30
 #define alox_UartMessage_cache_status_request_tag 33
 #define alox_UartMessage_cache_status_response_tag 34
+#define alox_UartMessage_espnow_echo_ping_request_tag 35
+#define alox_UartMessage_espnow_echo_ping_response_tag 36
 
 /* Struct field encoding specification for nanopb */
 #define alox_UartMessage_FIELDLIST(X, a) \
@@ -703,7 +737,9 @@ X(a, STATIC,   ONEOF,    MESSAGE,  (payload,battery_status_response,payload.batt
 X(a, STATIC,   ONEOF,    MESSAGE,  (payload,tap_notify_request,payload.tap_notify_request),  29) \
 X(a, STATIC,   ONEOF,    MESSAGE,  (payload,tap_notify_response,payload.tap_notify_response),  30) \
 X(a, STATIC,   ONEOF,    MESSAGE,  (payload,cache_status_request,payload.cache_status_request),  33) \
-X(a, STATIC,   ONEOF,    MESSAGE,  (payload,cache_status_response,payload.cache_status_response),  34)
+X(a, STATIC,   ONEOF,    MESSAGE,  (payload,cache_status_response,payload.cache_status_response),  34) \
+X(a, STATIC,   ONEOF,    MESSAGE,  (payload,espnow_echo_ping_request,payload.espnow_echo_ping_request),  35) \
+X(a, STATIC,   ONEOF,    MESSAGE,  (payload,espnow_echo_ping_response,payload.espnow_echo_ping_response),  36)
 #define alox_UartMessage_CALLBACK NULL
 #define alox_UartMessage_DEFAULT NULL
 #define alox_UartMessage_payload_ack_payload_MSGTYPE alox_Ack
@@ -735,6 +771,8 @@ X(a, STATIC,   ONEOF,    MESSAGE,  (payload,cache_status_response,payload.cache_
 #define alox_UartMessage_payload_tap_notify_response_MSGTYPE alox_TapNotifyResponse
 #define alox_UartMessage_payload_cache_status_request_MSGTYPE alox_CacheStatusRequest
 #define alox_UartMessage_payload_cache_status_response_MSGTYPE alox_CacheStatusResponse
+#define alox_UartMessage_payload_espnow_echo_ping_request_MSGTYPE alox_EspNowEchoPingRequest
+#define alox_UartMessage_payload_espnow_echo_ping_response_MSGTYPE alox_EspNowEchoPingResponse
 
 #define alox_Ack_FIELDLIST(X, a) \
 
@@ -934,6 +972,20 @@ X(a, STATIC,   SINGULAR, UINT32,   seq,               2)
 #define alox_EspNowUnicastTestResponse_CALLBACK NULL
 #define alox_EspNowUnicastTestResponse_DEFAULT NULL
 
+#define alox_EspNowEchoPingRequest_FIELDLIST(X, a) \
+X(a, STATIC,   SINGULAR, UINT32,   client_id,         1) \
+X(a, STATIC,   SINGULAR, UINT64,   timestamp_us,      2)
+#define alox_EspNowEchoPingRequest_CALLBACK NULL
+#define alox_EspNowEchoPingRequest_DEFAULT NULL
+
+#define alox_EspNowEchoPingResponse_FIELDLIST(X, a) \
+X(a, STATIC,   SINGULAR, BOOL,     success,           1) \
+X(a, STATIC,   SINGULAR, UINT32,   client_id,         2) \
+X(a, STATIC,   SINGULAR, UINT64,   timestamp_us,      3) \
+X(a, STATIC,   SINGULAR, UINT32,   esp_rtt_us,        4)
+#define alox_EspNowEchoPingResponse_CALLBACK NULL
+#define alox_EspNowEchoPingResponse_DEFAULT NULL
+
 #define alox_LedRingProgressRequest_FIELDLIST(X, a) \
 X(a, STATIC,   SINGULAR, UINT32,   mode,              1) \
 X(a, STATIC,   SINGULAR, UINT32,   progress,          2) \
@@ -1057,6 +1109,8 @@ extern const pb_msgdesc_t alox_CacheClientStatus_msg;
 extern const pb_msgdesc_t alox_CacheStatusResponse_msg;
 extern const pb_msgdesc_t alox_EspNowUnicastTestRequest_msg;
 extern const pb_msgdesc_t alox_EspNowUnicastTestResponse_msg;
+extern const pb_msgdesc_t alox_EspNowEchoPingRequest_msg;
+extern const pb_msgdesc_t alox_EspNowEchoPingResponse_msg;
 extern const pb_msgdesc_t alox_LedRingProgressRequest_msg;
 extern const pb_msgdesc_t alox_LedRingProgressResponse_msg;
 extern const pb_msgdesc_t alox_EspNowFindMeRequest_msg;
@@ -1099,6 +1153,8 @@ extern const pb_msgdesc_t alox_OtaSlaveProgressResponse_msg;
 #define alox_CacheStatusResponse_fields &alox_CacheStatusResponse_msg
 #define alox_EspNowUnicastTestRequest_fields &alox_EspNowUnicastTestRequest_msg
 #define alox_EspNowUnicastTestResponse_fields &alox_EspNowUnicastTestResponse_msg
+#define alox_EspNowEchoPingRequest_fields &alox_EspNowEchoPingRequest_msg
+#define alox_EspNowEchoPingResponse_fields &alox_EspNowEchoPingResponse_msg
 #define alox_LedRingProgressRequest_fields &alox_LedRingProgressRequest_msg
 #define alox_LedRingProgressResponse_fields &alox_LedRingProgressResponse_msg
 #define alox_EspNowFindMeRequest_fields &alox_EspNowFindMeRequest_msg
@@ -1136,6 +1192,8 @@ extern const pb_msgdesc_t alox_OtaSlaveProgressResponse_msg;
 #define alox_CacheStatusRequest_size             0
 #define alox_CacheStatusResponse_size            736
 #define alox_ClientInput_size                    22
+#define alox_EspNowEchoPingRequest_size          17
+#define alox_EspNowEchoPingResponse_size         25
 #define alox_EspNowFindMeRequest_size            6
 #define alox_EspNowFindMeResponse_size           8
 #define alox_EspNowUnicastTestRequest_size       12

main/proto/uart_messages.proto

@@ -29,6 +29,8 @@ enum MessageType {
   reserved 28;
   /** Combined cached accel + tap poll (one UART round-trip, ~16 ms cadence). */
   CACHE_STATUS = 29;
+  /** Host → master → slave → master: timestamp echo round-trip (latency test). */
+  ESPNOW_ECHO_PING = 30;
 }
 
 message UartMessage {
@@ -63,6 +65,8 @@ message UartMessage {
     TapNotifyResponse tap_notify_response = 30;
     CacheStatusRequest cache_status_request = 33;
     CacheStatusResponse cache_status_response = 34;
+    EspNowEchoPingRequest espnow_echo_ping_request = 35;
+    EspNowEchoPingResponse espnow_echo_ping_response = 36;
   }
 }
 
@@ -255,6 +259,22 @@ message EspNowUnicastTestResponse {
   uint32 seq = 2;
 }
 
+/** Host → master: ESP-NOW echo ping to one slave (timestamp echoed back). */
+message EspNowEchoPingRequest {
+  uint32 client_id = 1;
+  /** Microseconds since Unix epoch (host clock). */
+  uint64 timestamp_us = 2;
+}
+
+message EspNowEchoPingResponse {
+  bool success = 1;
+  uint32 client_id = 2;
+  /** Echoed host timestamp from goTool request. */
+  uint64 timestamp_us = 3;
+  /** esp_timer_get_time() delta from ping send to pong recv (master→slave→master). */
+  uint32 esp_rtt_us = 4;
+}
+
 // Host → master: LED ring on master (client_id=0) and/or slaves via ESP-NOW.
 // mode: 0=clear, 1=progress (0–100 %), 2=digit (0–10), 3=blink, 4=find-me, 5=all LEDs solid color.
 message LedRingProgressRequest {

main/uart.c

@@ -52,7 +52,8 @@ void init_uart(QueueHandle_t cmd_queue) {
       .flow_ctrl = UART_HW_FLOWCTRL_DISABLE,
   };
 
-  err = uart_driver_install(UART_NUM, UART_BUF_SIZE * 2, UART_BUF_SIZE, 0, NULL, 0);
+  err = uart_driver_install(UART_NUM, UART_DRIVER_RX_BUF_SIZE,
+                            UART_DRIVER_TX_BUF_SIZE, 0, NULL, 0);
   if (err != ESP_OK) {
     ESP_LOGE(TAG, "uart_driver_install failed: %s", esp_err_to_name(err));
     return;

main/uart.h

@@ -16,7 +16,10 @@
 #define UART_RXD_PIN 3
 
 
-#define UART_BUF_SIZE 2048
+#define UART_BUF_SIZE 4096
+/** Driver RX ring — must hold a full OTA block burst (~20 × ~215 B frames). */
+#define UART_DRIVER_RX_BUF_SIZE 16384
+#define UART_DRIVER_TX_BUF_SIZE 4096
 #define START_MARKER 0xAA
 #define STOP_MARKER 0xCC
 #define MAX_BUF_SIZE 252