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?

[Cecil Benjamin L]

Analog mic  -> ADC I2S out (TLV320ADC3100)-> I2S -> Raspberry Pi (RPi) (master)

Analog mic  -> ADC I2S out (TLV320ADC3100)-> I2S -> nRF(master)

This is the experimental setup. The i2s clocks generated by RPi and by nRF are of same value. Adc configuration are also same. 

I couldn't pinpoint the exact problem why nRF based implementation doesn't work.

[Edvin]

Did you try to check the bit and/or byte order of the data coming from the TLV? Bit byte swapping should be done similar to the way it is done in the snippet. And remember that your samples are 20 bit, so it looks like your example of 0xFD5A is missing 4 bits?

BR,

Edvin