TWI in Low Power...

[Brian]

Hey guys,

Trying to use TWI in the lowest power way possible, non-blocking. Is this the right way to do it? When I run this, I get the callback event handler to execute once, and once only -- seemingly stuck in WFE() or sd_app_evt_wait() , not waking up with the callback. Any ideas as to why?

  nrf_drv_twi_init(&p_twi_instance, &p_twi_config, twi_event_handler); 
  nrf_drv_twi_enable(&p_twi_instance); // Enable the TWI instance   

while(1) {
 
    nrf_drv_twi_rx(&p_twi_instance, 0x55, dummy_data, 7, false);          

    //power_manage(); //sd_app_evt_wait(); //if using SD                                                                                                                                        
    __WFE();   
}
    
static void twi_event_handler(nrf_drv_twi_evt_t *p_evt){   
    if(p_evt->type == NRF_DRV_TWI_RX_DONE)
    {

      SEGGER_RTT_printf(0, "\n\nDATA: ", dummy_data);
      for(i=0;i<7;i++) SEGGER_RTT_printf(0, "%02x ", dummy_data[i]);

    } 
}

[MartinBL]

Hi. Are you sure the handler is only called once? You might get a lot of other events that is not detected by your if-statement.

Also, I don't know your application but, but a lot of TWI sensors, memory chips, etc, need you to do a TWI TX operation first to tell which address in the device to read from. With nrf_drv_twi_rx() you just tell a device on a specific address "give me data!". You don't tell the device what data you want and this might cause troubles on your TWI bus. Try to add

[...]
else
{
   SEGGER_RTT_printf(0, "\n\nTWI ERROR: %d ", p_evt->error_src);
}

Or something to listen for other TWI events.

[MartinBL]

Error 2 is

NRF_TWI_ERROR_ADDRESS_NACK = TWI_ERRORSRC_ANACK_Msk,    /**< NACK received after sending the address. */

as defined in nrf_twi.h

So I guess you don't get any response from your external device?