Added ECHO cmd and fixed some timing issues

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":