Problem with nrf51822 in spi slave mode

[Sean]

Hello all

I making some device with ARM core CPU with nRF51822.

I set CPU to SPI master and set nRF51822 to slave. And then I read some data from nRF51822, that was always "0x55" or "0xAA". That depend on configuration of POL and PHA in master side.

Do you guess what is wrong?

B. Regards,

[Sean]

Dear Stefan Birnir Sverrisson

I set 1 ms delay before and after CSN HIGH.

Here is my using code in master and slave.

Could you find something wrong in this?

For Master (just pseudocode)

spi_test()
{
spi_init();
spi_cs_enable(); // LOW
spi_write( 0x33, 1 );
delay( 1ms );
spi_cs_disable(); // HIGH
delay( 1ms );

spi_cs_enable();
read = spi_read( 1 );
delay( 1ms );
spi_cs_disable();
delay(1ms);
}

For slave

static void spi_slave_event_handle(spi_slave_evt_t event)
{
uint32_t err_code;

if (event.evt_type == SPI_SLAVE_XFER_DONE)
{ 
    led_toggle();
    
    //Check if buffer size is the same as amount of received data.
    APP_ERROR_CHECK_BOOL(event.rx_amount == RX_BUF_SIZE);

    // loop back
    for( i=0 ; i<event.rx_amount ; i++ )
    {
      m_tx_buf[i] = m_rx_buf[i];
    }

    //Set buffers.
    err_code = spi_slave_buffers_set(m_tx_buf, m_rx_buf, sizeof(m_tx_buf), sizeof(m_rx_buf));
    APP_ERROR_CHECK(err_code);          
}
}

[Stefan Birnir Sverrisson]

My question is also, what data is in the m_tx_buf buffer. When spi_slave_event_handle is entered, the SPI transaction is finished and you have already sent the data in the m_tx_buf buffer to the SPI master. Your loopback function writes the data into the m_tx_buf buffer but that will only be sent to the master next time the SPI master clocks out a byte. So my guess is that if you clock out another byte, then you might get 0x33 back to the SPI master. Also, is the RX_BUF_SIZE == 1? If not, code execution will not exceed the error check APP_ERROR_CHECK_BOOL.