This example is to show how to use the APIs of Hands-Free Audio Gateway (hf_ag) Component and the effects of them by providing a set of commands. You can use this example to communicate with a device that implements Hands-Free Client Role (e.g. a headphone set).
This example is designed to run on commonly available ESP32 development board, e.g. ESP32-DevKitC. To operate this example, it should be connected to a Hands-Free Client running on a Headphone/Headset or on another ESP32 development board loaded with [hfp_hf](../hfp_hf) example of ESP-IDF.
- PCM: To use PCM, audio stream is directed from Bluetooth controller to the specific GPIO pins you set in the demo, and you should link these GPIO pins to a speaker via I2S port. The audio data will not go through the `Bluedroid`. In menuconfig, you should choose PCM in `menuconfig` path:
- vHCI: To use vHCI, audio data stream will be directed from Bluetooth Controller through vHCI on ESP32 and go through the Bluedroid to the Application layer. In menuconfig, you should choose vHCI in `menuconfig` path:
PCM Signal supports three configurations in menuconfig: PCM Role, PCM Polar and Channel Mode(Stereo/Mono).
- PCM Role: PCM role can be configured as PCM master or PCM slave. The default configuration is `Master`, you can change the PCM role in `menuconfig` path:
`Component config --> Bluetooth --> Controller Options --> PCM Signal Configurations --> PCM Signal Configurations: Role, Polar and Channel Mode(Stereo/Mono) --> PCM Role`
- PCM Polar: PCM polarity can be configured as Falling Edge or Rising Edge. The default configuration is `Falling Edge`, you can change the PCM polar in `menuconfig` path:
`Component config --> Bluetooth --> Controller Options --> PCM Signal Configurations --> PCM Signal Configurations: Role, Polar and Channel Mode(Stereo/Mono) --> PCM Polar`
- Channel Mode(Stereo/Mono): PCM frame synchronization signal can be configured as Stereo mode or Mono mode, where the Mono mode can be configured in two different forms(Mono mode 1 and Mono mode 2). As is shown in the figure 
- Stereo Mode(Dual channel): FSYNC and DOUT signals both change simultaneously on the edge of CLK. The FSYNC signal continues until the end of the current channel-data transmission.
- Mono Mode 1(Single channel): FSYNC signal starts to change a CLK clock cycle earlier than the DOUT signal, which means that the FSYNC signal takes effect a clock cycle earlier than the first bit of the current channel-data transmission. The FSYNC signal continues for one extra CLK clock cycle.
- Mono Mode 2(Single channel): FSYNC and DOUT signals both change simultaneously on the edge of CLK. The FSYNC signal continues for one extra CLK clock cycle.
- The default configuration is `Stereo Mode`, you can change the PCM Channel mode in `menuconfig` path:
`Component config --> Bluetooth --> Controller Options --> PCM Signal Configurations --> PCM Signal Configurations: Role, Polar and Channel Mode(Stereo/Mono) --> Channel Mode(Stereo/Mono)`
`CVSD` is the default setting and is also the widely used codec for voice audio. But, `mSBC` is designed to have a better voice quality through `HFP`. To select which one is in use, we provide `Wide Band Speech` item in the `menuconfig`:
Switching on the `Wide Band Speech` means that the preferred codec is `mSBC`, but which one is actually being used also depends on the `Data Path` configuration.
- If you choose `PCM` for datapath, you can only use `CVSD` and hardware is responsible for the codec job. In the meanwhile, you cannot use `mSBC` by switching `Wide Band Speech` on, because the `mSBC` is implemented in the Bluedroid (Bluetooth Host Stack) by software.
- If you choose `vHCI` for datapath with `Wide Band Speech` on, codec job is done in the Bluedroid and mSBC is being used.
- If you choose `vHCI` for datapath with `Wide Band Speech` off, hardware is responsible for the codec job and `CVSD` is in use.
Build the project and flash it to the board. Then, run monitor tool to view serial output:
```
idf.py -p PORT flash monitor
```
(Replace PORT with the name of the serial port to use.)
(To exit the serial monitor, type ``Ctrl-]``.)
See the [Getting Started Guide](https://docs.espressif.com/projects/esp-idf/en/latest/get-started/index.html) for full steps to configure and use ESP-IDF to build projects.
I (2221) BT_APP_HF: APP HFP event: CONNECTION_STATE_EVT
I (2221) BT_APP_HF: --connection state CONNECTED, peer feats 0x0, chld_feats 0x0
I (2291) BT_APP_HF: APP HFP event: CIND_RESPONSE_EVT
I (2291) BT_APP_HF: --CIND Start.
I (2331) BT_APP_HF: APP HFP event: CONNECTION_STATE_EVT
I (2331) BT_APP_HF: --connection state SLC_CONNECTED, peer feats 0xff, chld_feats 0x4010
```
**Note: Only after Hands-free Profile(HFP) service is initialized and a service level connection exists between an HF Unit and an AG device, could other commands be available.**
ESP32 supports both CVSD and mSBC codec. HF Unit and AG device determine which codec to use by exchanging features during service level connection. The choice of codec also depends on the your configuration in `menuconfig`.
Since CVSD is the default codec in HFP, we just show the scenarios using mSBC:
- If you enable `BT_HFP_WBS_ENABLE` in `menuconfig`, mSBC will be available.
- If both HF Unit and AG support mSBC and `BT_HFP_WBS_ENABLE` is enabled, ESP32 chooses mSBC.
- If you use PCM data path, mSBC is not available.
You can type `vron` to start the voice recognition and type `vroff` to terminate this function in the AG device. Both commands will notify the HF Unit the status of voice recognition. For example, type `vron` and the log will print:
You can type `ciev <ind_type> <value>` to send device status of AG to HF Unit. Log on AG prints such as: `Device Indicator Changed!` and on HF Unit side prints such as:
You can type `iron` to enable the in-band ring tone and type `iroff` to disable it. The log on the AG side prints such as `Device Indicator Changed!` and on HF Unit side it prints such as:
- Not all commands in the table are supported by the HF Unit.
- If you want to `hf con;` to establish a service level connection with a specific HF Unit, you should add the MAC address of the HF Unit in `app_hf_msg_set.c` for example: `esp_bd_addr_t peer_addr = {0xb4, 0xe6, 0x2d, 0xeb, 0x09, 0x93};`
- Use `esp_hf_client_register_callback()` and `esp_hf_client_init();` before establishing a service level connection.
## Example Breakdown
Due to the complexity of the HFP, this example has more source files than other bluetooth examples. To show the functions of HFP in a simple way, we use the Commands and Effects scheme to illustrate APIs of the HFP in ESP-IDF.
- For the voice interface, ESP32 has provided PCM input/output signals which can be directed to GPIO pins. So, please go to `gpio_pcm_config.c` for the configuration details.
- If you want to update the command table, please refer to `app_hf_msg_set.c`.
- If you want to update the responses of the AG or want to update the log, please refer to `bt_app_hf.c`.
- The task configuration part is in `bt_app_core.c`.
