gagarinlg · Oct 15, 2026 · Oct 15, 2026 · Oct 15, 2026 · Oct 15, 2026 · Oct 15, 2026
diff --git a/AGENTS.md b/AGENTS.md
@@ -92,8 +92,10 @@ Key invariants:
   CRSF/Ghost are forwarded raw. The module is a pure passthrough.
 - Master trainer = central (`AT+ROLE1`), slave/telemetry = peripheral
   (`AT+ROLE0`).
-- The firmware stays at 115200 baud; `AT+BAUD4` is acknowledged implicitly by
-  EdgeTX switching to 115200 without checking a response.
+- UART starts at 115200 for the EdgeTX boot handshake. `AT+BAUD4` selects
+  115200; `AT+BAUD6` selects 460800 for mono 16 kHz A2DP PCM. Both baud changes
+  have no response, so EdgeTX must switch its UART immediately after sending
+  the command.
 
 ## Build & test
 

diff --git a/README.md b/README.md
@@ -20,6 +20,7 @@ Documentation: https://btwifimod.gitbook.io/
 | Auto-connect to the last known device | Supported |
 | Device name from `AT+NAME` (persisted and advertised) | Supported |
 | Selectable BLE host: Bluedroid or NimBLE | Supported |
+| Classic A2DP audio source (Bluedroid, Classic-BT boards) | Supported |
 
 ## How telemetry works
 
@@ -49,8 +50,9 @@ service (`0xFFF0`, characteristic `0xFFF6`, NOTIFY).
 
 ## Wiring
 
-The module talks to the radio over a 3.3 V UART link (8N1, 115200 baud). Only
-TX, RX and GND are required; add +5V if the module is powered from the radio.
+The module talks to the radio over a 3.3 V UART link (8N1, 115200 baud at
+startup). A2DP PCM mode can switch the link to 460800 baud. Only TX, RX and GND
+are required; add +5V if the module is powered from the radio.
 The data lines are **crossed**: the module TX goes to the radio RX and the
 module RX to the radio TX. Keep GND common with the radio, and power the module
 from a supply that can handle the ESP32 current peaks.
@@ -74,12 +76,16 @@ The last two rows are the reference, non-validated targets (see
 
 ## EdgeTX protocol
 
-The module speaks the FrSky Bluetooth AT protocol over an 8N1 UART link at
-115200 baud. All responses are `\r\n`-terminated; the real ACK that advances
-EdgeTX is the `Central:<addr>` / `Peripheral:<addr>` line emitted after
-`AT+TXPW` / `AT+ROLE`. Trainer and S.Port frames are `0x7E`-delimited and
-byte-stuffed, while CRSF/Ghost are forwarded raw. See `AGENTS.md` for the full
-set of protocol invariants.
+The module speaks the FrSky Bluetooth AT protocol over an 8N1 UART link. The
+link starts at 115200 baud for the boot handshake. `AT+BAUD4` selects 115200;
+`AT+BAUD6` selects 460800 for mono A2DP PCM. Baud commands have no response, so
+EdgeTX must switch its UART immediately after sending the command. A2DP audio
+input is raw signed 16-bit little-endian mono PCM at 16 kHz; the module
+resamples it for the Bluetooth sink. All AT responses are `\r\n`-terminated;
+the real ACK that advances EdgeTX is the `Central:<addr>` / `Peripheral:<addr>`
+line emitted after `AT+TXPW` / `AT+ROLE`. Trainer and S.Port frames are
+`0x7E`-delimited and byte-stuffed, while CRSF/Ghost are forwarded raw. See
+`AGENTS.md` for the full set of protocol invariants.
 
 ## Code structure
 
@@ -109,14 +115,15 @@ doc/BENCH.md      Bench setup, procedure and validation status.
 PlatformIO (ESP-IDF). Two BLE hosts are selectable: Bluedroid (default) or
 NimBLE.
 
-**Supported targets** (app partition 1 MB):
+**Supported targets** (Bluedroid builds for Classic-Bluetooth boards also carry
+the A2DP source and use the 1.34 MB `pico_partitions.csv` app partition):
 
-| Environment | BLE host | Flash | Board |
-|---|---|---|---|
-| `C3SuperMini` | Bluedroid | ~84 % | ESP32-C3 SuperMini |
-| `C3SuperMini_nimble` | NimBLE | ~52 % | ESP32-C3 SuperMini |
-| `ESP32_DEV38P` | Bluedroid | ~86 % | ESP32-DEV-38P |
-| `ESP32_DEV38P_nimble` | NimBLE | ~53 % | ESP32-DEV-38P |
+| Environment | BLE host | App partition | Flash | Board |
+|---|---|---|---|---|
+| `C3SuperMini` | Bluedroid | 1 MB | ~84 % | ESP32-C3 SuperMini |
+| `C3SuperMini_nimble` | NimBLE | 1 MB | ~52 % | ESP32-C3 SuperMini |
+| `ESP32_DEV38P` | Bluedroid + A2DP | 1.34 MB | ~91 % | ESP32-DEV-38P |
+| `ESP32_DEV38P_nimble` | NimBLE | 1 MB | ~53 % | ESP32-DEV-38P |
 
 **Reference targets** (app partition 1.31 MB via `pico_partitions.csv`, not
 hardware-validated):
@@ -192,18 +199,72 @@ module:
 
 | Command | Meaning |
 |---|---|
-| `AT+BAUD4` | baud rate level (this firmware stays at 115200) |
+| `AT+BAUD4` | switch to 115200 baud |
+| `AT+BAUD6` | switch to 460800 baud for mono A2DP PCM |
 | `AT+NAME<name>` | set the Bluetooth name (persisted and advertised) |
 | `AT+TXPW<n>` | TX power (acknowledged) |
 | `AT+ROLE0` | Peripheral (telemetry / trainer slave) |
 | `AT+ROLE1` | Central (trainer master) |
-| `AT+DISC?` | start a scan (central) |
+| `AT+DISC?` | scan BLE in Central mode or Classic Bluetooth in A2DP mode |
 | `AT+CON<addr>` | connect to a device (central) |
+| `AT+A2DPON` | enable the Classic Bluetooth A2DP source |
+| `AT+A2DPCON<addr>` | connect to an A2DP sink (12 hex digits, no separators) |
+| `AT+A2DPOFF` | stop A2DP and turn Bluetooth off |
+| `AT+A2DPVOL<n>` | set AVRCP absolute volume (0..127) |
+| `AT+A2DPVOL?` | query AVRCP's 128 logical volume values |
+| `AT+A2DPSTART` / `AT+A2DPSTOP` | play or stop the A2DP sink |
+| `AT+BLEON` / `AT+BLEOFF` | enable the last BLE role / disable BLE |
+| `AT+BTOFF` | turn Bluetooth off |
 | `AT+CLEAR` | forget the saved device |
 | `AT+HTRESET` | reset the headtracker (BTWifiModule extension) |
 
 Responses: `OK+...`, `Central:<addr>`, `Peripheral:<addr>`, `Connected:<addr>`,
-`DisConnected`, `ERROR`.
+`DisConnected`, `A2DPVOL:<n>` (unsolicited sink volume update, 0..127), `ERROR`.
+AVRCP exposes a logical range of 0..127; it does not report the speaker's
+physical volume-detent count.
+
+A2DP is enabled in the Bluedroid configuration of every Classic-Bluetooth board
+(Radiomaster Pico and ESP32-DEV-38P) and never in the NimBLE build, which is
+BLE-only. On the ESP32-DEV-38P the AT link is UART2 (GPIO18 TX / GPIO19 RX) while
+logs stay on the CP2102 port (UART0), so A2DP is driven from a USB-UART adapter or
+the radio, not the log port.
+For a test without EdgeTX PCM input, build and flash `RM_pico_a2dp_test`; it
+streams a local 500 Hz tone. Connect to a discoverable sink with:
+
+```text
+AT+A2DPON
+AT+DISC?
+AT+A2DPCON<12-digit-address>
+```
+
+After the connection is established, send `AT+BAUD6` before transmitting PCM.
+To return to the normal radio link speed, send `AT+BAUD4` at 460800 baud.
+For PC-fed audio, install `pyserial` on Windows:
+
+```powershell
+py -m pip install pyserial
+```
+
+Prepare a mono, 16-bit PCM WAV at 16 kHz. If needed, convert an audio file with
+FFmpeg:
+
+```powershell
+ffmpeg -i input.mp3 -ac 1 -ar 16000 -c:a pcm_s16le audio.wav
+```
+
+Flash the normal `RM_pico` firmware (not `RM_pico_a2dp_test`, which uses its
+internal tone), close PuTTY, then run the sender. It probes at 115200 and
+460800, resets and restarts the A2DP stack, and restores 115200 if it detects a
+460800 session. It defaults to COM4 and the sink MAC `FC58FAACAA1A`:
+
+```powershell
+py tools\uart_audio_sender.py audio.wav
+```
+
+Override either default with `--port` or `--address`. The sender switches the
+module and PC to 460800, verifies the new rate, and prebuffers audio before
+connecting. It returns both sides to 115200 when playback ends. If neither baud
+probe receives a response, reset the module and retry.
 
 ## Credits
 

diff --git a/doc/BENCH.md b/doc/BENCH.md
@@ -9,7 +9,10 @@ to repeat the same checks for each BLE host (Bluedroid and NimBLE).
 - ESP32-DEV-38P (ESP32 classic, `ESP32_DEV38P*`): radio UART on
   GPIO18 (TX) / GPIO19 (RX); logs on UART0 (its CP2102 bridge). Its auto-reset
   does not drive IO0, so enter download mode manually (hold BOOT, tap RESET)
-  before flashing.
+  before flashing. The Bluedroid build (`ESP32_DEV38P`) enables Bluetooth
+  Classic, so this single firmware provides both the BLE roles and the Classic
+  A2DP/AVRCP audio source; it uses the 1.34 MB `pico_partitions.csv` app
+  partition because the A2DP stack does not fit in the default 1 MB one.
 - Reference only (not validated): ESP32 Pico Kit (`pico32`, `pico32_nimble`,
   radio UART GPIO4 TX / GPIO5 RX) and Radiomaster Pico (`RM_pico`,
   `RM_pico_nimble`, radio UART GPIO1 TX / GPIO3 RX, console on UART1
@@ -68,7 +71,8 @@ response. Run it once per firmware variant.
 | `AT+TXPW<n>`   | `OK+Txpw:0` + mode line                             | -                      |
 | `AT+DISC?`     | `OK+DISCS`, `OK+DISC:<addr>` per peer, `OK+DISCE`   | central; peripheral none |
 | `AT+CLEAR`     | `OK+CLEAR`                                          | central; peripheral none |
-| `AT+BAUD<n>`   | no response (stays at 115200)                       | -                      |
+| `AT+BAUD4`     | no response; switches to 115200                     | -                      |
+| `AT+BAUD6`     | no response; switches to 460800                     | A2DP PCM               |
 | `AT+HTRESET`   | `OK+HTRESET`, or `ERROR` unless headtracker board   | -                      |
 | unknown        | no response                                         | -                      |
 
@@ -116,6 +120,24 @@ Notes:
   headtracker reads about -80 dBm on the module and -56 dBm on the phone.
   Range is therefore limited by the module antenna.
 
+## Classic A2DP audio source (Bluedroid, Classic-BT boards)
+
+Available on `ESP32_DEV38P` (Classic Bluetooth) and `RM_pico`; never on NimBLE.
+
+1. Drive the AT link (for the ESP32-DEV-38P a USB-UART adapter on GPIO18/19, not
+   the CP2102 log port) and send the sequence
+   `AT+A2DPON`, `AT+DISC?`, `AT+A2DPCON<12-digit-address>`.
+2. Expect `OK+A2DPON`, then `OK+DISCS` / `OK+DISC:<addr>` per sink / `OK+DISCE`
+   from the inquiry, and finally a started media stream.
+3. Volume: `AT+A2DPVOL<n>` (0..127), `AT+A2DPVOL?` to query, and unsolicited
+   `A2DPVOL:<n>` lines when the sink changes the absolute volume.
+4. PCM path: send `AT+BAUD6` after connecting and feed mono 16-bit LE PCM at
+   16 kHz over the AT link (or use `tools/uart_audio_sender.py`).
+5. `AT+A2DPSTOP` / `AT+A2DPSTART` control playback; `AT+A2DPOFF` stops A2DP and
+   turns Bluetooth off.
+
+BLE and A2DP cannot run at the same time: enabling one stops the other.
+
 ## Expected values (telemetry)
 
 | Sensor       | Data ID | Sent value | Displayed     |
@@ -154,6 +176,7 @@ headtracker (no board-to-board master run):
 | AT command bench (16 checks)            | PASS      | PASS   |
 | Slave: telemetry to the phone app       | PASS      | PASS   |
 | Headtracker: detect + channels + reset  | PASS      | PASS   |
+| Classic A2DP source + AVRCP volume      | PASS      | n/a    |
 
 ## Automated battery
 
@@ -188,5 +211,12 @@ Last run (A = NimBLE, B = Bluedroid, headtracker at -84 dBm):
 - `AT+DISC?` now cancels any in-progress scan first, so it also completes
   while the module is auto-connecting (previously it returned `OK+DISCS` with
   no `OK+DISCE`).
+- `tools/uart_audio_sender.py` waits for an `A2DP media started` line after
+  `AT+A2DPCON`. The firmware only emits that string from the `AT+A2DPON` handler
+  and as an `A2DP` log line; on the ESP32-DEV-38P the logs go to the CP2102 port
+  (UART0), not the AT link (UART2), so the wait can time out even though media is
+  streaming. The audio path itself is fine: streaming owned PCM at 460800 after
+  `AT+BAUD6` plays correctly. The handshake is only reliable on the Radiomaster
+  Pico, where the console and the AT link share UART0.
 - Telemetry app: connection can drop right after connecting when the
   S.Port frames are invalid (fixed by the checksum in `tools/sport_sender.py`).
diff --git a/platformio.ini b/platformio.ini
@@ -9,7 +9,7 @@
 
 [platformio]
 ; Primary development target.
-default_envs = C3SuperMini
+default_envs = RM_pico
 
 ; Common configuration for all ESP32 targets (ESP-IDF).
 ; espressif32@6.10.0 == ESP-IDF v5.4.0 (matches the repo's sdkconfig.* files).
@@ -98,6 +98,14 @@ build_flags =
     -DCPU_ESP32=y
     -DBLUETOOTH=y
 
+; A2DP test build: stream a local tone without radio PCM input.
+[env:RM_pico_a2dp_test]
+extends = env:RM_pico
+board_build.esp-idf.sdkconfig_path = sdkconfig.RM_pico
+build_flags =
+    ${env:RM_pico.build_flags}
+    -DA2DP_TEST_TONE
+
 ; Same board with the NimBLE host instead of Bluedroid.
 [env:RM_pico_nimble]
 extends = esp32
@@ -163,10 +171,14 @@ build_flags =
 ; ---------------------------------------------------------------------------
 ; ESP32-DEV-38P (ESP32 DevKit, 38 pins) — Bluedroid
 ; Radio UART on GPIO18 (TX) / GPIO19 (RX); logs on UART0.
+; Classic Bluetooth is enabled in sdkconfig.ESP32_DEV38P, so this single build
+; offers both the BLE roles and the Classic A2DP/AVRCP audio source. The A2DP
+; stack does not fit in the default 1 MB app partition, hence pico_partitions.csv.
 ; ---------------------------------------------------------------------------
 [env:ESP32_DEV38P]
 extends = esp32
 board = esp32_dev_38p
+board_build.partitions = pico_partitions.csv
 upload_protocol = esptool
 build_type = release
 monitor_speed = 115200

diff --git a/sdkconfig.ESP32_DEV38P b/sdkconfig.ESP32_DEV38P
@@ -371,14 +371,14 @@ CONFIG_ESPTOOLPY_FLASHFREQ_40M=y
 # CONFIG_ESPTOOLPY_FLASHFREQ_20M is not set
 CONFIG_ESPTOOLPY_FLASHFREQ="40m"
 # CONFIG_ESPTOOLPY_FLASHSIZE_1MB is not set
-CONFIG_ESPTOOLPY_FLASHSIZE_2MB=y
-# CONFIG_ESPTOOLPY_FLASHSIZE_4MB is not set
+# CONFIG_ESPTOOLPY_FLASHSIZE_2MB is not set
+CONFIG_ESPTOOLPY_FLASHSIZE_4MB=y
 # CONFIG_ESPTOOLPY_FLASHSIZE_8MB is not set
 # CONFIG_ESPTOOLPY_FLASHSIZE_16MB is not set
 # CONFIG_ESPTOOLPY_FLASHSIZE_32MB is not set
 # CONFIG_ESPTOOLPY_FLASHSIZE_64MB is not set
 # CONFIG_ESPTOOLPY_FLASHSIZE_128MB is not set
-CONFIG_ESPTOOLPY_FLASHSIZE="2MB"
+CONFIG_ESPTOOLPY_FLASHSIZE="4MB"
 # CONFIG_ESPTOOLPY_HEADER_FLASHSIZE_UPDATE is not set
 CONFIG_ESPTOOLPY_BEFORE_RESET=y
 # CONFIG_ESPTOOLPY_BEFORE_NORESET is not set
@@ -474,7 +474,25 @@ CONFIG_BT_BLUEDROID_PINNED_TO_CORE=0
 CONFIG_BT_BTU_TASK_STACK_SIZE=4096
 # CONFIG_BT_BLUEDROID_MEM_DEBUG is not set
 CONFIG_BT_BLUEDROID_ESP_COEX_VSC=y
-# CONFIG_BT_CLASSIC_ENABLED is not set
+CONFIG_BT_CLASSIC_ENABLED=y
+CONFIG_BT_ENC_KEY_SIZE_CTRL_VSC=y
+# CONFIG_BT_ENC_KEY_SIZE_CTRL_NONE is not set
+# CONFIG_BT_CLASSIC_BQB_ENABLED is not set
+CONFIG_BT_A2DP_ENABLE=y
+CONFIG_BT_AVRCP_ENABLED=y
+
+#
+# AVRCP Features
+#
+CONFIG_BT_AVRCP_CT_COVER_ART_ENABLED=y
+# end of AVRCP Features
+
+# CONFIG_BT_SPP_ENABLED is not set
+# CONFIG_BT_L2CAP_ENABLED is not set
+# CONFIG_BT_SDP_COMMON_ENABLED is not set
+# CONFIG_BT_HFP_ENABLE is not set
+# CONFIG_BT_HID_ENABLED is not set
+CONFIG_BT_GOEPC_ENABLED=y
 CONFIG_BT_BLE_ENABLED=y
 CONFIG_BT_GATTS_ENABLE=y
 # CONFIG_BT_GATTS_PPCP_CHAR_GAP is not set
@@ -690,16 +708,31 @@ CONFIG_BT_BLE_RPA_TIMEOUT=900
 #
 # Controller Options
 #
-CONFIG_BTDM_CTRL_MODE_BLE_ONLY=y
+# CONFIG_BTDM_CTRL_MODE_BLE_ONLY is not set
 # CONFIG_BTDM_CTRL_MODE_BR_EDR_ONLY is not set
-# CONFIG_BTDM_CTRL_MODE_BTDM is not set
+CONFIG_BTDM_CTRL_MODE_BTDM=y
 CONFIG_BTDM_CTRL_BLE_MAX_CONN=2
-CONFIG_BTDM_CTRL_BR_EDR_SCO_DATA_PATH_EFF=0
+CONFIG_BTDM_CTRL_BR_EDR_MAX_ACL_CONN=2
+CONFIG_BTDM_CTRL_BR_EDR_MAX_SYNC_CONN=0
+# CONFIG_BTDM_CTRL_BR_EDR_SCO_DATA_PATH_HCI is not set
+CONFIG_BTDM_CTRL_BR_EDR_SCO_DATA_PATH_PCM=y
+CONFIG_BTDM_CTRL_BR_EDR_SCO_DATA_PATH_EFF=1
+CONFIG_BTDM_CTRL_PCM_ROLE_EDGE_CONFIG=y
+CONFIG_BTDM_CTRL_PCM_ROLE_MASTER=y
+# CONFIG_BTDM_CTRL_PCM_ROLE_SLAVE is not set
+CONFIG_BTDM_CTRL_PCM_POLAR_FALLING_EDGE=y
+# CONFIG_BTDM_CTRL_PCM_POLAR_RISING_EDGE is not set
+CONFIG_BTDM_CTRL_PCM_FSYNCSHP_STEREO_MODE=y
+# CONFIG_BTDM_CTRL_PCM_FSYNCSHP_MONO_MODE_LF is not set
+# CONFIG_BTDM_CTRL_PCM_FSYNCSHP_MONO_MODE_FF is not set
 CONFIG_BTDM_CTRL_PCM_ROLE_EFF=0
 CONFIG_BTDM_CTRL_PCM_POLAR_EFF=0
 CONFIG_BTDM_CTRL_PCM_FSYNCSHP_EFF=0
+# CONFIG_BTDM_CTRL_AUTO_LATENCY is not set
+CONFIG_BTDM_CTRL_LEGACY_AUTH_VENDOR_EVT=y
+CONFIG_BTDM_CTRL_LEGACY_AUTH_VENDOR_EVT_EFF=y
 CONFIG_BTDM_CTRL_BLE_MAX_CONN_EFF=2
-CONFIG_BTDM_CTRL_BR_EDR_MAX_ACL_CONN_EFF=0
+CONFIG_BTDM_CTRL_BR_EDR_MAX_ACL_CONN_EFF=2
 CONFIG_BTDM_CTRL_BR_EDR_MAX_SYNC_CONN_EFF=0
 CONFIG_BTDM_CTRL_PINNED_TO_CORE_0=y
 # CONFIG_BTDM_CTRL_PINNED_TO_CORE_1 is not set
@@ -2203,7 +2236,9 @@ CONFIG_BLUEDROID_PINNED_TO_CORE_0=y
 CONFIG_BLUEDROID_PINNED_TO_CORE=0
 CONFIG_BTU_TASK_STACK_SIZE=4096
 # CONFIG_BLUEDROID_MEM_DEBUG is not set
-# CONFIG_CLASSIC_BT_ENABLED is not set
+CONFIG_CLASSIC_BT_ENABLED=y
+CONFIG_A2DP_ENABLE=y
+# CONFIG_HFP_ENABLE is not set
 CONFIG_GATTS_ENABLE=y
 # CONFIG_GATTS_SEND_SERVICE_CHANGE_MANUAL is not set
 CONFIG_GATTS_SEND_SERVICE_CHANGE_AUTO=y
@@ -2377,12 +2412,14 @@ CONFIG_BLUFI_INITIAL_TRACE_LEVEL=2
 CONFIG_SMP_ENABLE=y
 # CONFIG_BLE_ACTIVE_SCAN_REPORT_ADV_SCAN_RSP_INDIVIDUALLY is not set
 CONFIG_BLE_ESTABLISH_LINK_CONNECTION_TIMEOUT=30
-CONFIG_BTDM_CONTROLLER_MODE_BLE_ONLY=y
+# CONFIG_BTDM_CONTROLLER_MODE_BLE_ONLY is not set
 # CONFIG_BTDM_CONTROLLER_MODE_BR_EDR_ONLY is not set
-# CONFIG_BTDM_CONTROLLER_MODE_BTDM is not set
+CONFIG_BTDM_CONTROLLER_MODE_BTDM=y
 CONFIG_BTDM_CONTROLLER_BLE_MAX_CONN=2
+CONFIG_BTDM_CONTROLLER_BR_EDR_MAX_ACL_CONN=2
+CONFIG_BTDM_CONTROLLER_BR_EDR_MAX_SYNC_CONN=0
 CONFIG_BTDM_CONTROLLER_BLE_MAX_CONN_EFF=2
-CONFIG_BTDM_CONTROLLER_BR_EDR_MAX_ACL_CONN_EFF=0
+CONFIG_BTDM_CONTROLLER_BR_EDR_MAX_ACL_CONN_EFF=2
 CONFIG_BTDM_CONTROLLER_BR_EDR_MAX_SYNC_CONN_EFF=0
 CONFIG_BTDM_CONTROLLER_PINNED_TO_CORE=0
 CONFIG_BTDM_CONTROLLER_HCI_MODE_VHCI=y