Use SPI Master within NUS Data Handler

Question

Hi,

I can use the SPI master functionality within nrf_drv_spi.c/.h just fine (i.e. calls from main) until I connect to my nRF52840 and utilize NUS. If I try to issue a nrf_drv_spi_transfer() call from within my NUS data handler (i.e. when handing incoming data over NUS) to read 2 registers from a SPI connected slave (I am the master), I am not getting the expected SPI event handler with event NRF_DRV_SPI_EVENT_DONE when a SPI transfer completes. In the code below, I am calling bmi160_spiReadRegs() from within my NUS data handler. This function is blocking because m_xfer_done is never set to TRUE as a result of spi_event_handler() being called.

void spi_event_handler(nrf_drv_spi_evt_t const * p_event,
                       void *                    p_context)
{
  // The only type passed to this handler is "NRF_DRV_SPI_EVENT_DONE"
  m_xfer_done = true;  
}

void spi_init()
{
  ret_code_t err_code;

  if(m_initialized) { return; } // Nothing to do.

  nrf_drv_spi_config_t spi_config = NRF_DRV_SPI_DEFAULT_CONFIG;
  spi_config.ss_pin   = ACC_SPI_CSN;          // Driver control.
  spi_config.miso_pin = ACC_SPI_MISO;
  spi_config.mosi_pin = ACC_SPI_MOSI;
  spi_config.sck_pin  = ACC_SPI_SCK;
  spi_config.mode     = NRF_DRV_SPI_MODE_0;   // Prev BMI160 exp.
  spi_config.frequency = NRF_DRV_SPI_FREQ_8M; // Max Nordic SPI Speed - chip max is 10M
  spi_config.bit_order = NRF_DRV_SPI_BIT_ORDER_MSB_FIRST; // From prev egs.
  err_code = nrf_drv_spi_init(&spi, &spi_config, spi_event_handler, NULL);
  APP_ERROR_CHECK(err_code);

  m_initialized = true;
}

///////////////////////////////////////////////////////////////////////////
// BMI160.c slave functions for read/write via SPI. Fcn signature is set.
///////////////////////////////////////////////////////////////////////////

int8_t bmi160_spiReadRegs(uint8_t dev_addr, uint8_t reg_addr, uint8_t *p_data, short unsigned int data_len)
{
  ret_code_t err_code;
  uint8_t* p_newRxBuf;

  // Watch for this to change to true in handler.
  m_xfer_done = false;

  // Cannot continue if not initialized.
  if(!m_initialized) { return 1; }

  // Add read bit to register. 
  reg_addr = reg_addr | SPI_READ_MASK;

  // Create a rx buffer that has an extra byte for the response (first byte back is ignored as per egs).
  p_newRxBuf = malloc(data_len + 1);
  memset(p_newRxBuf, 0, data_len+1);

  // Read directly into p_data. nrf_drv_spi_transfer() should hold down cs to ensable values from all regs.
  // as specified by data_len.
  err_code = nrf_drv_spi_transfer(&spi, &reg_addr, 1, p_newRxBuf, data_len+1);
  APP_ERROR_CHECK(err_code);

  // Wait for a result.
  while(!m_xfer_done) { nrf_delay_ms(1); }

  // Copy Rx data into p_data
  memcpy(p_data, p_newRxBuf+1, data_len);

  free(p_newRxBuf);
  
  return 0;
}

If I issue the same SPI read on main using nrf_drv_spi_transfer(), the SPI event handler is called with event NRF_DRV_SPI_EVENT_DONE as expected. But, if I issue the nrf_drv_spi_transfer() from my NUS data handler, my SPI event handler is never called (at all).

I see other references to similar issues on DevZone. For these issues, NUS or SPI priority changes are suggested. I have tried this, but to no avail.

Specifically, I have set NRFX_SPI_DEFAULT_CONFIG_IRQ_PRIORITY to 2 to match NUS, but to no avail. See below.

// <o> NRFX_SPI_DEFAULT_CONFIG_IRQ_PRIORITY  - Interrupt priority
 
// <0=> 0 (highest) 
// <1=> 1 
// <2=> 2 
// <3=> 3 
// <4=> 4 
// <5=> 5 
// <6=> 6 default
// <7=> 7 

#ifndef NRFX_SPI_DEFAULT_CONFIG_IRQ_PRIORITY
#define NRFX_SPI_DEFAULT_CONFIG_IRQ_PRIORITY 2
#endif

I have also tried changing the priority of NUS to match SPI. I set it to 6 as below.

// <o> BLE_NUS_BLE_OBSERVER_PRIO  
// <i> Priority with which BLE events are dispatched to the UART Service.
// Default 2

#ifndef BLE_NUS_BLE_OBSERVER_PRIO
#define BLE_NUS_BLE_OBSERVER_PRIO 6
#endif

Neither of these addressed the issue. If I call nrf_drv_spi_transfer() within my NUS data handler, the SPI event handler is never called with event NRF_DRV_SPI_EVENT_DONE.

This confuses me as the NUS UART example calls UART reads/writes within the NUS data handler and the UART priority is the same as SPI (both 6).

Perhaps this is not priority related?

Help, clues, etc are appreciated.

Thanks,

Mark J

Mark J · Accepted Answer

I was able to resolve this by simply scheduling a handler on the main thread from the NUS data hander. There may also be a way to resolve through priority changes, but I will leave it to a Nordic expert to suggest such a change.

Use SPI Master within NUS Data Handler

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