SPI configuration for nrf52832

[Marc]

I've configured the SPI with DMA module as in the code below.

I've loaded the tx buffer with sample data and start the transaction; however, I'm not reading anything either on the MOSI pin or the MISO pin. The SCK pin also stays low. The tx and rx end events do go from 0 to 1 correctly.

Any ideas what I'm doing wrong?

Thanksspi code.rtf

[hmolesworth]

Ha ha! I had to smile at this one .. my answer I posted earlier below I think really is the issue, but we didn't look far enough :-) so GPIO->OUTSET does exactly what I said it does, as you concurred, but of course so does GPIO->OUTCLR .. any pins which are high are erroneously driven low because of this:

  NRF_GPIO->OUTCLR |= 1 << CSPIN;  //drive cs low to initiate spi comm

Change to this and your code works fine:

  NRF_GPIO->OUTCLR = 1 << CSPIN;  //drive cs low to initiate spi comm

This can be an interview question ..

[Marc]

I made the changes you suggested. Actually the chip select pin is separate from the spi module. It shouldn't have any effect on the clock and data signals. I still don't get anything on the mosi line after the start task is initiated.

[Marc]

Here's the amended code with your changes. I also put in a loop for sending continuously the same data. There's still nothing on the MOSI line.

#define CSPIN 11  //spi chip select
#define SCKPIN 12  //spi clock
#define MOSIPIN 13  //spi mosi
#define MISOPIN 14  //spi miso

int main()
{
  NRF_GPIO->PIN_CNF[CSPIN] = 1;  //output
  NRF_GPIO->PIN_CNF[SCKPIN] = 1;  //output
  NRF_GPIO->PIN_CNF[MOSIPIN] = 1;  //output
  NRF_GPIO->PIN_CNF[MISOPIN] = 0;  //input pin, input buffer connected, no pull, S0S1, sense disabled
  NRF_SPIM0->PSEL.SCK = SCKPIN;
  NRF_SPIM0->PSEL.MOSI = MOSIPIN;
  NRF_SPIM0->PSEL.MISO = MISOPIN;
  NRF_SPIM0->CONFIG = 0b010;  //CPOL 0 -- clock polarity active high, CPHA 1 -- sample on trailing clock edge, send Msb first
  NRF_SPIM0->FREQUENCY = 0x02000000;  //250 kbps
  uint8_t spiTXBuf[2];  //2 byte tx buffer
  uint8_t spiRXBuf[2];  //2 byte rx buffer
  spiTXBuf[0] = 0b10101010;  //example byte
  spiTXBuf[1] = 0b10101010;  //example byte
  NRF_SPIM0->TXD.PTR = (uint32_t)((uint8_t *)spiTXBuf);
  NRF_SPIM0->TXD.MAXCNT = 2;
  NRF_SPIM0->RXD.PTR = (uint32_t)((uint8_t *)spiRXBuf);
  NRF_SPIM0->RXD.MAXCNT = 2;
  NRF_SPIM0->ENABLE = 7;  //enabled
  while(1)
  {
    NRF_SPIM0->EVENTS_ENDTX = 0;
    NRF_SPIM0->EVENTS_ENDRX = 0;
    NRF_GPIO->OUTCLR = 1 << CSPIN;  //drive cs low to initiate spi comm
    for(uint8_t i = 0; i < 21; i++) __asm__("nop\n\t");  //low for 21 machine instructions
    NRF_SPIM0->TASKS_START = 1;
    while(!NRF_SPIM0->EVENTS_ENDTX);  //last byte transmitted
    while(!NRF_SPIM0->EVENTS_ENDRX);  //last byte received
    NRF_SPIM0->TASKS_STOP = 1;
    for(uint8_t i = 0; i < 3; i++) __asm__("nop\n\t");
    NRF_GPIO->OUTSET = 1 << CSPIN;
    for(uint8_t i = 0; i < 21; i++) __asm__("nop\n\t");
  }
}