USB Audio Half Used Packets

RE: USB Audio Half Used Packets

Andrew — Mon, 18 Jun 2018 14:21:14 GMT

Do'h! I was getting lost in mix of samples versus bytes.

Thanks for the help.

RE: USB Audio Half Used Packets

Håkon Alseth — Mon, 18 Jun 2018 10:53:37 GMT

Hi,

This is the code that fetches the EP size and sets 192 bytes to m_temp_buffer_size:

size_t rx_size = app_usbd_audio_class_rx_size_get(&m_app_audio_headphone.base);
m_temp_buffer_size = rx_size;

Which in turn checks that specific endpoint and returns the OUT SIZE (read from NRF_USBD->SIZE.ISOOUT, since this is an isochronous transfer) which the PC sends:

size_t app_usbd_audio_class_rx_size_get(app_usbd_class_inst_t const * p_inst)
{
    nrf_drv_usbd_ep_t ep_addr;

    ep_addr = ep_iso_addr_get(p_inst);
    ASSERT(NRF_USBD_EPISO_CHECK(ep_addr));

    return (size_t)nrf_drv_usbd_epout_size_get(ep_addr);
}

Remember that "int16_t m_temp_buffer[96];" will be equal to 192 bytes in memory.

Best regards,

Håkon

RE: USB Audio Half Used Packets

Andrew — Fri, 15 Jun 2018 17:20:47 GMT

Thanks for responding! Yes, I am still seeing this. I am thinking it is a matter of buffer size definition.

I have only added code to aggregate the samples into a lager buffer.

#define GRAB_DATA
#ifdef GRAB_DATA
static int16_t muchLargerBuffer[1000];
static unsigned int bigCount = 0;
static unsigned int smallCount = 0;
#endif


/**
 * @brief User event handler @ref app_usbd_audio_user_ev_handler_t (headphones)
 */
static void hp_audio_user_ev_handler(app_usbd_class_inst_t const * p_inst,
                                     app_usbd_audio_user_event_t   event)
{
    app_usbd_audio_t const * p_audio = app_usbd_audio_class_get(p_inst);
    UNUSED_VARIABLE(p_audio);
    switch (event)
    {
        case APP_USBD_AUDIO_USER_EVT_CLASS_REQ:
            hp_audio_user_class_req(p_inst);
            break;
        case APP_USBD_AUDIO_USER_EVT_RX_DONE:
        {
            ret_code_t ret;
            /* Block from headphones copied into buffer, send it into microphone input */
            #ifdef GRAB_DATA
            if(bigCount<99000){
                bigCount += m_temp_buffer_size;
            }
            else if(bigCount<100000){
                memcpy(muchLargerBuffer+smallCount, m_temp_buffer, m_temp_buffer_size);
                bigCount += m_temp_buffer_size;
                smallCount += m_temp_buffer_size;
            }
            else{
                NRF_LOG_INFO("Stop Here!");
            }
            #endif
            ret = app_usbd_audio_class_tx_start(&m_app_audio_microphone.base, m_temp_buffer, m_temp_buffer_size);
            if (NRF_SUCCESS == ret)
            {
                bsp_board_led_invert(LED_AUDIO_RX);
            }
            break;
        }
        default:
            break;
    }
}

The size of the buffer, m_temp_buffer, is 2*48=96 but the size of the data sent is 192. More specifically, m_temp_buffer_size is found to be 192 when watched in the debugger.

I see 192 pop up in one more place, at the audio class definition. However, I am not sure what the "Endpoint size" is supposed to be the size of any way.

So it looks like data I am getting delivered is 96 bytes in size, like I would expect, but the size that is sent through to the usbd audio class is double that, which doesn't make sense.

RE: USB Audio Half Used Packets

Håkon Alseth — Tue, 12 Jun 2018 14:30:46 GMT

Hi,

Sorry for the late reply. Are you still seeing this issue?

Which version of the nRF52840 are you using? Note that engineering A (pca10056 v0.9.x and lower) workarounds have been removed from SDK 15.

Also, have you edited the example in any way? I see that all samples in the m_temp_buffer is filled up with non-zero values.

The example is setup with a buffer size of 48 (times 2 for stereo, equals 192 bytes on the USB descriptor side), so I do not see how you should see 96 samples of zeroes unless the audio stream is such.

Best regards,

Håkon

RE: USB Audio Half Used Packets

Andrew — Wed, 02 May 2018 16:57:54 GMT

Stereo. When you do stereo the samples are interleaved. Therefore, more specifically, the packet contains 48 samples of left and 48 samples of right.

RE: USB Audio Half Used Packets

Turbo J — Wed, 02 May 2018 16:32:18 GMT

Mono vs. stereo?