Audio & LE Audio¶

IPRO7 has an audio ADC (AUADC) for analog and PDM microphones, a 10-bit DAC (GPDAC) and I2S. The SDK puts a capture and an output framework on top of them in components/audio, adds LC3 and other codecs, USB audio through CherryUSB, and the LE Audio profiles of the BLE host. On the IPRO7AI Reef EVK the out-of-box firmware ipro7ai_reef_demo drives every audio block from the shell, and its src/audio.c is the reference code for this page.

Architecture¶

flowchart LR
  PDM["PDM mic"] --> AUADC["AUADC"]
  HS["Headset mic (J2)"] --> AUADC
  AUADC --> CAP["audio_capture"]
  CAP --> APP["Application<br/>(record, monitor, ASRC)"]
  APP --> OUT["audio_output"]
  OUT --> DAC["GPDAC → speaker amp / headphones"]
  OUT --> UAC["USB UAC → host"]
  ISO["LE Audio ISO (CIS)"] --> DEC["LC3 decode"] --> HDAC["Headset DAC path"]

Audio hardware¶

The audio blocks of the IPRO7AI Reef EVK V4.0 and the board-header names that code uses for them (bsp/board/ipro7/ipro7ai_reef_board_config.h):

• The headphone jack always gets the DAC signal. "Headphones only" means keeping the speaker amplifier off; there is no other routing switch.
• The PDM path does not run at exactly 16,000 Hz: nominally 15,875 Hz (2.032 MHz / 128), measured at about 15,872 Hz on a Reef. mic sdrec writes the measured rate into the WAV header, and mic usb converts to the host's 16,000 Hz with audio_asrc.
• The DAC backend of audio_output runs at a fixed 32 kHz (DAC_RATE in audio_capture.h); other sample rates are resampled.
• The amplifier gain is high (30 V/V in the demo README); the demo plays tones at 20 % amplitude by default.
• Set CONFIG_DMA_CHANNEL_ALLOCATOR=y so capture, playback and the USB isochronous endpoint get DMA channels at run time without clashing.

Jack type, connector and the full pin map are on the IPRO7AI Reef EVK page. The IPRO7 EVB and the IPRO7AI EVK have their own audio examples (ipro_pdm_mic_demo, ipro7ai_evk_demo); see their board pages.

Audio framework¶

CONFIG_AUDIO_OUTPUT=y
CONFIG_AUDIO_CAPTURE=y
CONFIG_DMA_CHANNEL_ALLOCATOR=y
# USB microphone through the audio_output UAC backend
CONFIG_COMPONENTS_CHERRYUSB_ENABLE=y
CONFIG_CHERRYUSB_DEVICE=y
CONFIG_CHERRYUSB_DEVICE_AUDIO=y

The resampler, the clock-drift resampler (audio_asrc), the speaker EQ and bass boost are always built.

How the pieces are used:

• audio_capture_init() takes an audio_capture_cfg_t (source type, sample rate, frame size, and the PDM or analog settings), audio_capture_add_consumer() returns a consumer id with its own buffer, audio_capture_start() starts the DMA, and audio_capture_read(id, buf, bytes, timeout_ms) returns PCM.
• audio_output_create() takes an audio_output_cfg_t. In AUDIO_OUTPUT_MODE_STREAMING the output plays continuously from a cyclic DMA ring and audio_output_write(out, pcm, samples) blocks only briefly when the ring is full; AUDIO_OUTPUT_MODE_ONESHOT blocks until the whole buffer has played. The third argument of audio_output_write() counts samples per channel, not bytes.
• For the DAC backend, pass the amplifier enable pin and its active level (dac_spk_gpio, dac_spk_en_active); audio_output_start() switches the amplifier on.

Hands-on on the Reef¶

Record three seconds from the PDM microphone, play them back on the headphones, then record a WAV file to the SD card and use the board as a USB microphone. Everything runs in ipro7ai_reef_demo; the excerpts show the code you reuse in your own application.

To turn these checks into repeatable tests, see Test your application.

LE Audio¶

LE Audio carries LC3 audio over ISO channels: CIS for unicast, BIS for broadcast. On the receiving side the data path is:

flowchart LR
  P["Phone (unicast client)"] -->|"CIS"| C["Controller bt54_iso2"]
  C --> H["Host: ASCS / BAP"]
  H --> Q["Application queue"]
  Q --> D["LC3 decode task"]
  D --> O["DAC"]

Settings needed in .config (excerpt from ipro_le_audio_headset/defconfig_reef):

CONFIG_BT_CTLR_IPRO=y
CONFIG_IPRO_BLE_CTLR_LIB="link1_periph"
CONFIG_IPRO_BLE_CTLR_FEATURE="bt54_iso2"
CONFIG_IPRO_BLE_CTLR_CFG_DBG=y
CONFIG_EM_SIZE=32
CONFIG_BT_CONN=1
CONFIG_BT_SETTINGS=y
CONFIG_BT_AUDIO=y
CONFIG_BT_AUDIO_RX=y
CONFIG_COMPONENTS_LC3_ENABLE=y

The build does not resolve Kconfig dependencies, so start from the whole defconfig_reef rather than this excerpt; it also enables BAP, PACS, ASCS, ISO, CAP, CSIP and VCP. The controller archive rules are in BLE Development.

Unicast headset¶

apps/bluetooth/le_audio/ipro_le_audio_headset advertises as IPRO-LE-Audio; an LE Audio unicast client connects and sets up a CIS to the board.

make -C apps/bluetooth/le_audio/ipro_le_audio_headset DEFCONFIG=defconfig_reef   # output in build_reef/build_out/

On the Reef, defconfig_reef is the DAC variant: the output goes to the GPDAC (headphones on J2, speaker amplifier while no plug is in J2), SW3 and SW4 turn the volume down and up and SW5 mutes, through the VCP volume renderer. The other configurations of this application (.config, DAC.config, UAC.config) build for the IPRO7 EVB. Building, pairing and what to check are in Getting Started with LE Audio.

How src/bap_server.c registers PACS and ASCS (excerpt, simplified: logging and conditional compilation removed; unicast_server_cb is defined in the same file):

static const struct bt_audio_codec_cap lc3_sink_codec_cap =
    BT_AUDIO_CODEC_CAP_LC3(BT_AUDIO_CODEC_CAP_FREQ_16KHZ |
                       BT_AUDIO_CODEC_CAP_FREQ_32KHZ |
                       BT_AUDIO_CODEC_CAP_FREQ_48KHZ,
                   BT_AUDIO_CODEC_CAP_DURATION_7_5 |
                       BT_AUDIO_CODEC_CAP_DURATION_10 |
                       BT_AUDIO_CODEC_CAP_DURATION_PREFER_10,
                   BT_AUDIO_CODEC_CAP_CHAN_COUNT_SUPPORT(1),
                   26, 155, 1,
                   BT_AUDIO_CONTEXT_TYPE_MEDIA |
                       BT_AUDIO_CONTEXT_TYPE_CONVERSATIONAL);

static struct bt_pacs_cap lc3_sink_cap = {
    .codec_cap = &lc3_sink_codec_cap,
};

int bap_server_init(void)
{
    struct bt_pacs_register_param pacs_param = {
        .snk_pac = true,
        .snk_loc = true,
    };
    struct bt_bap_unicast_server_register_param server_param = {
        .snk_cnt = CONFIG_BT_ASCS_MAX_ASE_SNK_COUNT,
        .src_cnt = CONFIG_BT_ASCS_MAX_ASE_SRC_COUNT,
    };
    int err;

    err = bt_pacs_register(&pacs_param);                     /* 1. PACS service */
    if (err != 0 && err != -EALREADY) {
        return err;
    }
    err = bt_pacs_cap_register(BT_AUDIO_DIR_SINK, &lc3_sink_cap);  /* 2. LC3 capability */
    if (err != 0) {
        return err;
    }
    err = bt_pacs_set_location(BT_AUDIO_DIR_SINK, BT_AUDIO_LOCATION_FRONT_LEFT);
    if (err != 0) {
        return err;
    }
    bt_pacs_set_supported_contexts(BT_AUDIO_DIR_SINK,
                       BT_AUDIO_CONTEXT_TYPE_MEDIA |
                       BT_AUDIO_CONTEXT_TYPE_CONVERSATIONAL |
                       BT_AUDIO_CONTEXT_TYPE_UNSPECIFIED);
    bt_pacs_set_available_contexts(BT_AUDIO_DIR_SINK,
                       BT_AUDIO_CONTEXT_TYPE_MEDIA |
                       BT_AUDIO_CONTEXT_TYPE_CONVERSATIONAL |
                       BT_AUDIO_CONTEXT_TYPE_UNSPECIFIED);

    err = bt_bap_unicast_server_register(&server_param);      /* 3. ASCS endpoints */
    if (err != 0 && err != -EALREADY) {
        return err;
    }
    return bt_bap_unicast_server_register_cb(&unicast_server_cb);  /* 4. BAP callbacks */
}

Broadcast¶

No FreeRTOS application in this release does BIS broadcast. The host includes the bt_bap_broadcast_source_* and bt_bap_broadcast_sink_* APIs, and zephyr/samples/bap_broadcast_source and bap_broadcast_sink show them under Zephyr on the IPRO7 EVB and the IPRO7AI EVK; there is no Zephyr board for the Reef (see Zephyr RTOS).

Profiles¶

The host's subsys/bluetooth/audio/ holds the Zephyr v4.4.0 LE Audio profile sources (BAP, CAP, PACS, ASCS, VCP, CSIP, MICP, MCP, TMAP and more). The headset enables:

LC3¶

• Prebuilt library components/3rdparty/liblc3/lib/libliblc3.a with header lc3.h; add it with CONFIG_COMPONENTS_LC3_ENABLE=y.
• Bit rates from 16 to 320 kbps (LC3_MIN_BITRATE, LC3_MAX_BITRATE).
• Other codecs in components/3rdparty: SBC (libsbc), Opus (opus, used by ipro_agora_sentino), minimp3.

USB audio¶

USB audio uses CherryUSB's UAC device class on the Reef's USB-C (Full Speed):

CONFIG_COMPONENTS_CHERRYUSB_ENABLE=y
CONFIG_CHERRYUSB_DEVICE=y
CONFIG_CHERRYUSB_DEVICE_AUDIO=y

With CONFIG_AUDIO_OUTPUT=y as well, audio_output gets its UAC backend: create the output with .type = AUDIO_OUTPUT_UAC and write PCM to it as to the DAC. ipro7ai_reef_demo uses it in two commands:

Both enumerate as VID 0x3896, PID 0x0003. An application that implements its own USB audio device sets CONFIG_AUDIO_OUTPUT_UAC_EXCLUDE=y. The IPRO7 EVB examples ipro_pdm_mic_demo and the UAC.config of ipro_le_audio_headset have their own UAC devices.

PDM recording¶

ipro7ai_reef_demo records from the PDM microphone (pdm) or the headset microphone (headset):

• mic gain <dB> sets the playback make-up gain (0–40 dB, default 20 dB); mic ch <0|1> selects the PDM slot.
• mic status reports the last recording's peak, RMS and voice-band (300–3,400 Hz) level in dBFS. The first 100 ms after start are left out of those numbers because the decimator starts with a step.
• mic sdrec flushes the file every 30 s, so pulling the power loses at most the last 30 s. A measured rate more than 80 Hz away from the nominal 15,875 Hz is reported as lost samples, and the header then carries 15,875 Hz.
• A microphone monitored on the speaker howls; use headphones and hp.

The PDM recording example for the IPRO7 EVB and the IPRO7AI EVK is ipro_pdm_mic_demo (BLE transfer with LC3, Android companion source in tools/android/IproMicDemo/).

Limitations in this release¶

• ipro_le_audio_headset: audio playback from a phone is not yet validated (see its README); the headset has no source ASE and sends no microphone audio back.
• No FreeRTOS LE Audio broadcast example; broadcast exists only as Zephyr samples for the IPRO7 EVB and the IPRO7AI EVK.
• bt54_iso2 needs at least 32 KB of EM, while controller PDS sleep supports only the 16 KB EM profile, so the controller does not enter PDS in an LE Audio configuration.
• The Reef V4.0 has no line input; the aux source and the AUX-IN notes in the demo README describe the previous board.
• A USB-to-BLE audio bridge example is not included.

Related examples and documents¶

• Getting Started with LE Audio
• BLE Development: controller selection, bring-up order and GATT
• Audio API
• IPRO7AI Reef EVK: jack, speaker connector and pins