Delay between nrf_drv_uart_rx_abort (sends NRF_UARTE_TASK_STOPRX) to enter to event handler.

[VadymS]

Hi.

I work with PCA10040 and SKD_14.2. 

I use UARTE with easy DMA.
I see big enough delay between sending nrf_drv_uart_rx_abort and entering to UART event hanler. What is the latency should be in this case?

Thanks.

[Susheel Nuguru]

The smallest interrupt latency on Cortex M4 is 12 CPU cycles. There could be few more cycles added on chip design when adding more peripheral lines.

If you see significantly more latency, then it means that the CPU was busy handling other handler which is clearly higher in priority than the UART interrupt handler.

[VadymS]

This my own conclusion, when i returned to timing optimization of the project.

I see that few guys have the same problem with interrupt latency. 
NRF driver inserts significant delay to the interrupt handler latency, while the interrupt latency itself is in spec value.

[Susheel Nuguru]

Vadym, 

VadymS said:

NRF driver inserts significant delay to the interrupt handler latency

You are right that nrf drivers do insert some delay, but if it is significant or not depends on each use case. If someone is developing an application that has serious constraints on servicing the interrupt as fast as possible, then you could always strip away the features in that driver that you do not need and hence make the ISR smaller.