nrf52832 SPI Code execution time

RE: nrf52832 SPI Code execution time

Håkon Alseth — Tue, 10 Aug 2021 08:09:23 GMT

Hi,

[quote user="hannes"]I'm still not sure If there would be an improvement in moving something to the main context?[/quote]

In terms of speed, it isn't an improvement, but in terms of reducing time spent in interrupt; it will be. However, 40 us is not that costly timing wise.

Kind regards,

Håkon

RE: nrf52832 SPI Code execution time

hannes — Tue, 10 Aug 2021 08:01:24 GMT

Thanks Håkon,

removing "__WFE()" speeded it up to 40 microseconds which is pretty good for my application. I'm still not sure If there would be an improvement in moving something to the main context?

RE: nrf52832 SPI Code execution time

Håkon Alseth — Mon, 09 Aug 2021 13:42:42 GMT

Hi,

[quote user="hannes"]

The IRQ-priorities are set as:

GPIOTE_CONFIG_IRQ_PRIORITY 6
SPI_DEFAULT_CONFIG_IRQ_PRIORITY 5

Is this OK?

[/quote]

Yes, that is fine.

[quote user="hannes"]thank's very much for your detailed answer. I'm not sure how to implement the SPI-while() loop in main as I'm already using idle_state_handle(); in main like in the nordic BLE-Examples. Can you please tell me how to get theese things together in my code example?[/quote]

You are still handling this directly in two interrupt vectors, with no scheduling (ie. offloading processing) to main. If you want to speed up, remove the "__WFE()" call in getValues().

Since the call "nrf_drv_spi_transfer()" is effectively a blocking call due to your next line while(!spi_xfer_done), the minimum time for those interrupts is equal to the time it takes to transfer those bytes over SPI.

Kind regards,

Håkon

RE: nrf52832 SPI Code execution time

hannes — Mon, 09 Aug 2021 11:38:24 GMT

Hi Håkon,

thank's very much for your detailed answer. I'm not sure how to implement the SPI-while() loop in main as I'm already using idle_state_handle(); in main like in the nordic BLE-Examples. Can you please tell me how to get theese things together in my code example?

The IRQ-priorities are set as:

GPIOTE_CONFIG_IRQ_PRIORITY 6
SPI_DEFAULT_CONFIG_IRQ_PRIORITY 5

Is this OK?

Thank you very much in advance!

void getValues(uint8_t sensor[])
{
    APP_ERROR_CHECK(nrf_drv_spi_transfer(&spi, m_tx_buf, 1, m_rx_buf, 2));
    while (!spi_xfer_done) { __WFE(); }		
    spi_xfer_done = false;
}


static void int_handler(nrf_drv_gpiote_pin_t pin, nrf_gpiote_polarity_t action)
{
    uint8_t   sensor[2];
    getValues(sensor);
}

void spi_event_handler(nrf_drv_spi_evt_t const * p_event, void *p_context)
{
    spi_xfer_done = true;
}


int main(void)
{
    initialize_nrf;
    initialize_nrf_ble;
    initialize_sersor_via_spi;

    for (;;)
    {
        idle_state_handle();
    }
}

RE: nrf52832 SPI Code execution time

Håkon Alseth — Fri, 06 Aug 2021 11:47:35 GMT

Hi,

[quote user=""]So adding this line of code seems to speed up the execution time of the SPI commands[/quote]

Compilers optimize in the strangest ways.

If you are triggering a SPI transaction from the GPIOTE irq vector, you should avoid to do this in the interrupt handler:

* logging

* sleeping

Please also note that if you set the same priority on the two IRQs, you will get into a while(1) loop on the spi_xfer_done call.

This will essentially take as long as it takes to:

* Handle two interrupt vectors

* Send and receive over SPI

If you want to make the ISR functions run quicker, disable logging, and move the while() loop to main context.

Kind regards,

Håkon