SPIS not working with S140 softdevice on nRF52840

RE: SPIS not working with S140 softdevice on nRF52840

Vidar Berg — Mon, 30 Mar 2020 15:35:17 GMT

Thank you for the update!

RE: SPIS not working with S140 softdevice on nRF52840

Maik — Mon, 30 Mar 2020 15:06:09 GMT

Found the problem:

static nrfx_spis_t spi_instance = NRFX_SPIS_INSTANCE( 0 ); // <- declare here

static void*   spi_defaultContext;
static uint8_t spi_defaultTxBuffer[2];
static uint8_t spi_defaultRxBuffer[2];

void spi_init( void )
{
  // snip

  nrfx_spis_buffers_set( spi_instance, spi_defaultTxBuffer, 2, spi_defaultRxBuffer.controlSequence, 2 );
}

We initialized p_instance in spi_init() and pointed the static pointer spi_instance to it.

--> pointer to a stack location that gets overwritten.

Thank you very much for the help!

RE: SPIS not working with S140 softdevice on nRF52840

Maik — Mon, 30 Mar 2020 14:18:33 GMT

We updated the handler as follows:

static void spi_evt_handler( nrfx_spis_evt_t const* p_event, void* p_contex )
{
  NRF_LOG_DEBUG( "Event: %d", p_event->evt_type);
  if( p_event->evt_type == NRFX_SPIS_BUFFERS_SET_DONE ) 
  {
    NRF_LOG_DEBUG( "Buffer set");
  }
  else if( ( p_event->evt_type == NRFX_SPIS_XFER_DONE ) )
  {
    NRF_LOG_DEBUG( "Transmission Done: %d, %d", p_event->rx_amount, p_event->tx_amount);
    APP_ERROR_CHECK( nrfx_spis_buffers_set( spi_instance, spi_defaultTxBuffer, 2, NULL, 0 ) );
  }
}

The result is the same.

We also added some logging to the event handler.

<debug> app: Event: 0
<debug> app: Buffer set


// snip

<debug> app: Event: 1
<debug> app: Transmission Done: 2, 2

We only get one event of type NRFX_SPIS_BUFFERS_SET_DONE and one of type NRFX_SPIS_XFER_DONE. Nothing for the second transmission.

RE: SPIS not working with S140 softdevice on nRF52840

Vidar Berg — Mon, 30 Mar 2020 13:14:31 GMT

Thanks. Looks like the TX buffer is set only once in the code you provided? It must be updated after every completed transaction by calling nrfx_spis_buffers_set().

RE: SPIS not working with S140 softdevice on nRF52840

Maik — Mon, 30 Mar 2020 12:48:36 GMT

Hey,

we also tried 100 uS and are getting the same result.

I hope the following snippets are enough.

static nrfx_spis_t const* spi_instance;

static void*   spi_defaultContext;
static uint8_t spi_defaultTxBuffer[2];
static uint8_t spi_defaultRxBuffer[2];


void spi_init( void )
{
  nrfx_spis_config_t p_config   = NRFX_SPIS_DEFAULT_CONFIG;
  nrfx_spis_t        p_instance = NRFX_SPIS_INSTANCE( 0 );
  spi_instance                  = &p_instance;
  p_config.miso_pin             = BLE_MISO_PIN;
  p_config.mosi_pin             = BLE_MOSI_PIN;
  p_config.sck_pin              = BLE_SCLK_PIN;
  p_config.csn_pin              = BLE_CS_PIN;
  p_config.def                  = 0xAA;
  p_config.orc                  = 0xBB;
  p_config.mode                 = NRF_SPIS_MODE_0;


  nrfx_spis_init( spi_instance, &p_config, (nrfx_spis_event_handler_t)spi_evt_handler, spi_defaultContext );

  NRF_POWER->TASKS_CONSTLAT = 1;

  spi_defaultRxBuffer[0] = 0x00;
  spi_defaultRxBuffer[1] = 0x00;

  spi_defaultTxBuffer[0] = 0xDE;
  spi_defaultTxBuffer[1] = 0xAD;

  nrfx_spis_buffers_set( spi_instance, spi_defaultTxBuffer, 2, spi_defaultRxBuffer.controlSequence, 2 );
}

static void spi_evt_handler( nrfx_spis_evt_t const* p_event, void* p_contex )
{
// Empty
}


int main( void )
{
  log_init( );
  timers_init( );
  power_management_init( );
  spi_init( );
  ble_stack_init_( );
  
  //...

  // Enter main loop.
  for( ;; )
  {
    if( NRF_LOG_PROCESS( ) == false )
    {
      nrf_pwr_mgmt_run( );
    }
  }
}

RE: SPIS not working with S140 softdevice on nRF52840

Vidar Berg — Mon, 30 Mar 2020 11:33:37 GMT

Hello,

2uS would still be marginal if you were in LP mode. Could you try 10 us so we can exclude CS timing as a possible cause? This would give the SPIS plenty of time to acquire the semaphore. Also, could you post some code snippets of your SPIS implementation?

RE: SPIS not working with S140 softdevice on nRF52840

Maik — Mon, 30 Mar 2020 08:55:55 GMT

Hello,

We have the constant latency mode enabled.
The chipselect is done by the hardware, but we alternatively tried setting the spi-clock to 1 kHz, that should give plenty of time.

As you can see in the screenshot, the SPIS is still writing DEF (0xAA in our case).

Edit: We added a delay ( > 2 us) between CS low and the first clock.

In the following screenshot you can see the first transfer, which is working fine

The next screenshot shows the second transfer, which is sending out DEF (0xAA)

As far as our understanding goes, DEF is sent when the SPIS can't acquire the semaphore.

RE: SPIS not working with S140 softdevice on nRF52840

Vidar Berg — Fri, 27 Mar 2020 13:36:49 GMT

Hi,

The SPIS requires a bit more time to wake-up from low power System ON mode because it needs to wait for the HF clock to ramp up. This is why the SPIS example enables constant latency mode on startup:

    // Enable the constant latency sub power mode to minimize the time it takes
    // for the SPIS peripheral to become active after the CSN line is asserted
    // (when the CPU is in sleep mode).
    NRF_POWER->TASKS_CONSTLAT = 1;

Is it possible to assert the CSN line a bit earlier in your case so the slave gets more time to wake-up? It will probably be the most optimal solution in terms of power consumption. The constant latency mode would increase the base current from a few uA to about 500 uA.

Best regards,

Vidar