How to read I2S configuration and print in UART using NRF52-DK ?

[Cecil Benjamin L]

Hello,

I have an analogue audio mic connected to external ADC. The external ADC can give an output of 16bit, 20bits, 24bits and 32 bits I2S data. I have configured to send 20 bit as I2S output.

To enable the I2S communication between the ADC and NRF52 I use below configuration.

    config.sdin_pin  = I2S_SDIN_PIN;
    config.sdout_pin = NRFX_I2S_PIN_NOT_USED;
    config.mck_pin   = NRFX_I2S_PIN_NOT_USED;
    config.mck_setup = NRF_I2S_MCK_32MDIV15;
    config.ratio     = NRF_I2S_RATIO_48X;
    config.format    = NRF_I2S_FORMAT_I2S;
    config.sample_width  = NRF_I2S_SWIDTH_24BIT;
    config.channels      = NRF_I2S_CHANNELS_STEREO;

In the SDK config, I have selected the pin of SDIN as 28. SCK - 31 , LRCK - 30.

While debugging, I watch the RX buffer of the nrf_I2S the data to check values most of the time starts as 0xFF8 or 0xFF9 or 0x00.

I understand that if the 24-bit I2S communication is chosen then when storing NRF stores it with  0xFF"24bit value".

1. Can I communicated with 20 bits from the ADC side or should I use only 16 or 24?

2. If 20 bits can be configured then should I expect the RX buffer data should always starting as 0xFF0"20bits value"? Because I want to store it in SD card. So I need to store the raw data to a WAV header. And the raw data should be removed of first 12 bits.

When I use NRF RTT to print the 32-bit value from RX buffer it seems like NRF LOG stuck in a loop. Without NRF LOG statement I can see that RX buffer updating each time I debug. Need a suggestion for this problem as well.

Thanks

Cecil

[Cecil Benjamin L]

Can you suggest a solution for NRF LOG struck in a loop problem. I am print the whole buffer in a loop.

static bool check_samples(uint32_t const * p_block)
{
    // [each data word contains two 16-bit samples]
    uint16_t i;
    for (i = 0; i < I2S_DATA_BLOCK_WORDS; ++i)
    {
        uint32_t const * p_word = &p_block[i];
        uint32_t sample_actual = *p_word;
        NRF_LOG_INFO("P_word: 0x%x ",sample_actual);
        //Process data for SD card storage/ Uart print
    }
    NRF_LOG_INFO("%3u: OK", m_blocks_transferred);
    return true;
}

[Edvin]

Hello Cecil,

where is NRF_LOG stuck in a loop problem? What do you mean by this? Do you mean that the logs doesn't print correctly, or that it prints forever in a loop, e.g. the loop:

for (i = 0; i< I2S_DATA_BLOCK_WORDS; i++)

loop doesn't finish?

BR,

Edvin

[Cecil Benjamin L]

    NRF_LOG_INFO("%3u: OK", m_blocks_transferred);   

struck at above line.

The loop for (i = 0; i< I2S_DATA_BLOCK_WORDS; i++) doesn't finish because of this NRF_LOG problem.

[Edvin]

I am not sure why it is stuck (?). Do you mean stuck, or actually struck?

What does it look like? does NRF_LOG_INFO(); never return? If so, is it the first call to NRF_LOG_INFO, or after a while?

Please note that NRF_LOG_INFO() doesn't print immediately to the log. The log is printed when NRF_LOG_PROCESS() is called later in your main loop. 

Perhaps you can try to change:

#define NRF_LOG_DEFERRED 1
to
#define NRF_LOG_DEFERRED 0

in your sdk_config.h file. Does that help?

If not, can you replicate the issue in a project that doesn't require any external components other than the DK, and upload it here?

BR,

Edvin

[Cecil Benjamin L]

Currently I am using printf(); statement to print the buffer values. I think i can solve this NRF log problem later. My problem is the I2S data stored can't be verified. I printed all the values and used audacity to convert the raw data to an audio file. It seems it is always noise.  I am sure the ADC configuration is correct because I am using exact setup using raspberry pi.  Can you suggest on how I can handle the I2S data and confirm the received data is correct. 

[Edvin]

How do you confirm that the data is correct? 

Did you look into the snippets I suggested in my first reply? 

[Cecil Benjamin L]

My current nRF based experimental setup was replicated using Raspberry Pi few days back. I used the same I2S clock - BCLK, LRCK and I2C configuration for the ADC in Raspberry Pi. The experimental setup works in Raspberry Pi.

I plotted the raw data of nRF I2S SDIN in Matlab and also used audacity to convert the data to audio. Doesn't look like a sine wave at all.

I tired using a logic analyzer but seems like I2S decode in Picoscope doesn't help much.

[Edvin]

Cecil Benjamin L said:

I used the same I2S clock - BCLK, LRCK and I2C configuration for the ADC in Raspberry Pi. The experimental setup works in Raspberry Pi.

 I must say I am a bit confused.

Your setup is:

I2S microphone -> some device -> ADC -> I2S -> nRF?

Was this the same in your Raspberry Pi setup?

I2S microphone -> some device -> ADC -> I2S -> Raspberry Pi?