Send large BLE host frames across multiple notifies.

Prefer ATT MTU 517 and chunk oversized responses so CLIENT_INFO/BATTERY work with many pods; reset the goTool parser after timeouts so partial frames do not poison the next exchange.

Co-authored-by: Cursor <cursoragent@cursor.com>

main/ble_host.c

@@ -4,6 +4,7 @@
 #include "host_transport.h"
 #include "nvs_flash.h"
 #include "freertos/FreeRTOS.h"
+#include "freertos/semphr.h"
 #include "freertos/task.h"
 
 #include "nimble/nimble_port.h"
@@ -22,6 +23,12 @@ static const char *DEVICE_NAME = "Powerpod";
 #define BLE_CONN_ITVL_MIN_UNITS 6 /* 7.5 ms */
 #define BLE_CONN_ITVL_MAX_UNITS 6
 #define BLE_CONN_TUNE_MAX_TRIES 6
+/** Prefer large ATT MTU so CLIENT_INFO / BATTERY fit in fewer notify chunks. */
+#define BLE_PREFERRED_ATT_MTU 517
+#define BLE_NOTIFY_CHUNK_RETRIES 24
+#define BLE_NOTIFY_CHUNK_RETRY_MS 5
+/** Pace multi-chunk notifies so the central parser sees contiguous frame bytes. */
+#define BLE_NOTIFY_CHUNK_GAP_MS 8
 
 /*
  * Nordic UART style:
@@ -43,6 +50,7 @@ static bool notify_enabled;
 static uint16_t att_mtu = 23;
 static esp_timer_handle_t conn_tune_timer;
 static uint8_t conn_tune_tries;
+static SemaphoreHandle_t s_tx_mu;
 
 static int ble_gap_event(struct ble_gap_event *event, void *arg);
 static void ble_request_fast_conn_params(uint16_t handle);
@@ -61,28 +69,83 @@ uint16_t ble_host_max_payload(void) {
   return (uint16_t)(att_mtu - 3);
 }
 
-static esp_err_t ble_host_tx(const uint8_t *frame, size_t frame_len) {
-  struct os_mbuf *om;
-  int rc;
+/**
+ * One ATT notification (≤ MTU-3). Retries on transient NimBLE buffer pressure.
+ */
+static esp_err_t ble_notify_chunk(const uint8_t *data, uint16_t len) {
+  for (int attempt = 0; attempt < BLE_NOTIFY_CHUNK_RETRIES; attempt++) {
+    struct os_mbuf *om = ble_hs_mbuf_from_flat(data, len);
+    if (om == NULL) {
+      vTaskDelay(pdMS_TO_TICKS(BLE_NOTIFY_CHUNK_RETRY_MS));
+      continue;
+    }
 
+    int rc = ble_gatts_notify_custom(conn_handle, ble_chr_val_handle, om);
+    if (rc == 0) {
+      return ESP_OK;
+    }
+    /* Ownership stays with us on failure. */
+    os_mbuf_free_chain(om);
+    if (!ble_host_ready()) {
+      return ESP_ERR_INVALID_STATE;
+    }
+    ESP_LOGD(TAG, "notify chunk rc=%d attempt=%d len=%u", rc, attempt,
+             (unsigned)len);
+    vTaskDelay(pdMS_TO_TICKS(BLE_NOTIFY_CHUNK_RETRY_MS));
+  }
+  ESP_LOGW(TAG, "notify chunk gave up after retries len=%u", (unsigned)len);
+  return ESP_ERR_NO_MEM;
+}
+
+/**
+ * Send a full host frame. If larger than ATT MTU-3, split across consecutive
+ * notifies; goTool feeds every notify into the same byte parser, so the frame
+ * reassembles without a protocol change. Mutex keeps stream ticks from
+ * interleaving mid-frame.
+ */
+static esp_err_t ble_host_tx(const uint8_t *frame, size_t frame_len) {
   if (!ble_host_ready()) {
     return ESP_ERR_INVALID_STATE;
   }
-  if (frame_len == 0 || frame_len > ble_host_max_payload()) {
+  if (frame == NULL || frame_len == 0) {
+    return ESP_ERR_INVALID_ARG;
+  }
+
+  uint16_t max_chunk = ble_host_max_payload();
+  if (max_chunk == 0) {
     return ESP_ERR_INVALID_SIZE;
   }
 
-  om = ble_hs_mbuf_from_flat(frame, (uint16_t)frame_len);
-  if (om == NULL) {
-    return ESP_ERR_NO_MEM;
+  if (s_tx_mu == NULL ||
+      xSemaphoreTake(s_tx_mu, pdMS_TO_TICKS(2000)) != pdTRUE) {
+    return ESP_ERR_TIMEOUT;
   }
 
-  rc = ble_gatts_notify_custom(conn_handle, ble_chr_val_handle, om);
-  if (rc != 0) {
-    os_mbuf_free_chain(om);
-    return ESP_FAIL;
+  esp_err_t result = ESP_OK;
+  size_t off = 0;
+  while (off < frame_len) {
+    if (!ble_host_ready()) {
+      result = ESP_ERR_INVALID_STATE;
+      break;
+    }
+    size_t remain = frame_len - off;
+    uint16_t n =
+        (uint16_t)(remain > max_chunk ? max_chunk : remain);
+    result = ble_notify_chunk(&frame[off], n);
+    if (result != ESP_OK) {
+      ESP_LOGW(TAG, "TX abort at %u/%u (chunk %u, mtu_pay %u)",
+               (unsigned)off, (unsigned)frame_len, (unsigned)n,
+               (unsigned)max_chunk);
+      break;
+    }
+    off += n;
+    if (off < frame_len) {
+      vTaskDelay(pdMS_TO_TICKS(BLE_NOTIFY_CHUNK_GAP_MS));
+    }
   }
-  return ESP_OK;
+
+  xSemaphoreGive(s_tx_mu);
+  return result;
 }
 
 static void ble_conn_tune_timer_cb(void *arg) {
@@ -365,6 +428,12 @@ esp_err_t init_ble_host(QueueHandle_t cmd_queue) {
   host_transport_set_cmd_queue(cmd_queue);
   host_transport_set_tx(ble_host_tx);
 
+  s_tx_mu = xSemaphoreCreateMutex();
+  if (s_tx_mu == NULL) {
+    ESP_LOGE(TAG, "failed to create TX mutex");
+    return ESP_ERR_NO_MEM;
+  }
+
   /* NVS may already be init via pod_settings; ignore ALREADY_INIT. */
   ret = nvs_flash_init();
   if (ret == ESP_ERR_NVS_NO_FREE_PAGES ||
@@ -404,9 +473,11 @@ esp_err_t init_ble_host(QueueHandle_t cmd_queue) {
     return ESP_FAIL;
   }
 
-  rc = ble_att_set_preferred_mtu(247);
+  rc = ble_att_set_preferred_mtu(BLE_PREFERRED_ATT_MTU);
   if (rc != 0) {
     ESP_LOGW(TAG, "preferred MTU set failed: %d", rc);
+  } else {
+    ESP_LOGI(TAG, "preferred ATT MTU %u", (unsigned)BLE_PREFERRED_ATT_MTU);
   }
 
   nimble_port_freertos_init(ble_host_task);