SPIS communication corrupted

Question

Hey,

I'm using nRF as a SPI slave with a Raspberry Pi. I'm seeing that even at ~3MHz SPI frequency, my first byte transferred gets corrupted. I have a test setup where I'm sending 10 bytes (data sent is 1-10). I see that the first byte is incorrect a lot of times. These different errors were seen:

0x81(129) as the first byte, which is one bit-flip away from the expected 0x01.
0xFE(254) as the first byte, which is the Over-Read Character. Tested by changing ORC to 0xBB (187) and saw 187 then.
A shift in the sequence being sent and an additional 0x81 in the beginning.

image description

I also saw error #1 at frequencies lower than 3MHz.

I saw the Errata 109 but it seems that that is pertinent only if I'm using _WFE or PPI. I'm not using either one though.

Does anyone have any idea why this could be happening?

Thanks,

Vandita

I'm using nRF52832 with SDK 13.0.0. Using SPIS3.

The nrf code looks like this:

static uint32_t spis_send(uint8_t* rx_data, uint8_t rx_len,
                                  uint8_t* tx_data, uint8_t tx_len)
{
  uint32_t err_code = ERR_UNKNOWN;
  spis_xfer_done = false;
  err_code = nrf_drv_spis_buffers_set(&spis, tx_data, tx_len, rx_data, rx_len);
  if (ERR_SUCCESS == err_code)
  {
    err_code = ERR_FAILURE;
    uint32_t count = 0;
    while (!spis_xfer_done && (count < COUNT_MAX))
    {
      __WFE();
      count++;
    }
    if (spis_xfer_done)
    {
      err_code = ERR_SUCCESS;
    }
  }
  return err_code;
}

static void spis_event_handler(nrf_drv_spis_event_t event)
{
  if (event.evt_type == NRF_DRV_SPIS_XFER_DONE)
  {
    spis_xfer_done = true;
  }
}

void SPIS_send_fake_data()
{
  uint8_t rx_data = 0;
  uint8_t data_out[10] = {0};
  for (int i = 0; i < 10; ++i)
  {
    data_out[i] = i + 1;
  }
  spis_send(&rx_data, 0, data_out, 10);
}

void SPIS_init()
{
  printf("SPIS_init\r\n");
  nrf_drv_spis_config_t spis_config = NRF_DRV_SPIS_DEFAULT_CONFIG;
  spis_config.csn_pin = SCS_PIN;
  spis_config.miso_pin = MISO_PIN;
  spis_config.mosi_pin = MOSI_PIN;
  spis_config.sck_pin = SCK_PIN;
  spis_config.mode = NRF_DRV_SPIS_MODE_0;
  spis_config.bit_order = NRF_DRV_SPIS_BIT_ORDER_MSB_FIRST;
  spis_config.miso_drive = NRF_GPIO_PIN_H0H1;
  nrf_drv_spis_init(&spis, &spis_config, spis_event_handler);
}

On the pi side, my code looks like this:

bool init()
{
  bool ret_code = false;
  if (bcm2835_init())
  {
    if (bcm2835_spi_begin())
    {
      bcm2835_spi_setBitOrder(BCM2835_SPI_BIT_ORDER_MSBFIRST);  // The default
      bcm2835_spi_setDataMode(BCM2835_SPI_MODE0);               // The default
      // FIXME: any way to match 8 MHz?
      //      bcm2835_spi_setClockDivider(BCM2835_SPI_CLOCK_DIVIDER_64);  // ~
      //      6.25 MHz
      bcm2835_spi_setClockDivider(BCM2835_SPI_CLOCK_DIVIDER_128);  // ~ 3 MHz
      bcm2835_spi_chipSelect(BCM2835_SPI_CS0);                  // The default
      bcm2835_spi_setChipSelectPolarity(BCM2835_SPI_CS0, LOW);  // the default
      spdlog::get(APP_NAME)->info("Successfully initialized SPI!");
      ret_code = true;
      sleep(1);
    }
    else
      spdlog::get(APP_NAME)->error(
          "Failed to start SPI operations (ensure running as root)!");
  }
  else
    spdlog::get(APP_NAME)->error("Failed to initialize SPI!");

  return ret_code;
}

bool end()
{
  bool ret_code = false;
  bcm2835_spi_end();
  if (bcm2835_close() == 0) ret_code = true;

  return ret_code;
}

void spi_read_fake_data()
{
  char ouput_data[10] = {0};
  uint8_t data[10];
  bool error_seen = true;
  bcm2835_spi_transfernb(ouput_data, (char *)data, 10);
  for (int i = 0; i < 10; ++i)
  {
    if (data[i] == 0xFF || data[i] == 0)
    {
      error_seen = false;
    }
  }
  if (error_seen)
  {
    for (int i = 0; i < 10; ++i)
    {
      printf("%d ", data[i]);
    }
    printf("\r\n");
  }
}

Update dec 12: screenshots SPI Mode 0 Error#1. Seeing 0x81. 0x559us between CS going low and first rising edge of clock.

image description

SPI Mode 0 Error#2. Seeing 0xBB - ORC and also seeing 0x00 sent instead of 0x06. I've seen this at different places.

image description

SPI Mode 1. Seeing 0x81. image description