Accelerometer configuration issue

Question

Dear Concern,

we have tried to configure the accelerometer LSM6DSO module through SPI interface using NRF52xx DK board. External Module was not configured properly without minimum nrf_delay_ms(10). 
 Is any reason behind this delay, as it is not working without delay?

could you please give us the suggestion how to avoid delay and is there alternate solution?

Regards, 
 Srinivas Rao.

hmolesworth · Answer

Something to check, as this requirement for a delay often indicates a buffer inadvertently being placed on the stack and overwritten before the data has been completely used. In a function like this: 
 void mySpiStuff(void)
{
 uint8_t ctrl3_c_accelerometer[] = {1,2,3,4,5};
 if(nrf_drv_spi_transfer(&spi, ctrl3_c_accelerometer, sizeof(ctrl3_c_accelerometer), NULL, NULL) != NRFX_SUCCESS)
 {
 error = 12; return error;
 }
 //nrf_delay_ms(10); // Minimum delay required
 return ok;
}

void myOtherStuff(void)
{
 uint32_t stuff[8];
 .. blahBlah
}

void main(void)
{
 .. blahBlah
 mySpiStuff();
 myOtherStuff();
} 
 The problem is myOtherStuff() runs before the SPI transfer is complete, which clobbers the data in ctrl3_c_accelerometer before that data has completed the journey to the accelerometer. The fix is very simple, make ctrl3_c_accelerometer static, which moves the location off the stack and into safe memory: 
 uint32_t mySpiStuff(void)
{
 static uint8_t ctrl3_c_accelerometer[] = {1,2,3,4,5}; // <== use static!
 if(nrf_drv_spi_transfer(&spi, ctrl3_c_accelerometer, sizeof(ctrl3_c_accelerometer), NULL, NULL) != NRFX_SUCCESS)
 {
 error = 12; return error;
 }
 return ok;
} 
 If it's any help, experienced programmers can make this mistake, and it makes a good interview question.