Hardware timer stopped or not short cleared during interrupt

[DonalHE]

Hi There, I'm having problems with my hardware timer appearing to stop counting or not being cleared via a short when the timer interrupt is executing.

In my application, I have the following:

• Hardware TimerCounterA, configured to generate a compare event every 100uS. A short is configured in that timer to clear the timer when the compare event fires.
• Hardware TimerCounterB, configured in count mode, a PPI channel is used to connect the compare event on TimerCounterA to the count task on TimerCounterB.
• GPIOTE pin toggle, a pin is configured to be toggled via the fork option of the PPI channel which connects TimerCounterA and TimerCounterB

I am monitoring the toggled pin using an oscilloscope, and can see that when interrupts are enabled for TimerCounterA, there is an extra delay in the pin toggle of about 0.8uS. If I disabled this interrupt, then time between toggles of the pin is an accurate 100.0 uS.

I have a timers & GPIOTE configured as follows:

tTimerAConfig.frequency = NRF_TIMER_FREQ_16MHz;
tTimerAConfig.mode      = NRF_TIMER_MODE_TIMER;
tTimerAConfig.bit_width = NRF_TIMER_BIT_WIDTH_16;
tTimerAConfig.p_context = NULL;
tTimerAConfig.interrupt_priority = APP_IRQ_PRIORITY_LOW;
nrf_drv_timer_extended_compare(ptNrfTimerA, NRF_TIMER_CC_CHANNEL0, 1600, NRF_TIMER_SHORT_COMPARE0_CLEAR_MASK, false);
...
tTimerCounterBConfig.frequency = NRF_TIMER_FREQ_16MHz;
tTimerCounterBConfig.mode      = NRF_TIMER_MODE_COUNTER;
tTimerCounterBConfig.bit_width = NRF_TIMER_BIT_WIDTH_32;
tTimerCounterBConfig.p_context = NULL;
tTimerCounterBConfig.interrupt_priority = APP_IRQ_PRIORITY_MID;
...
// Configure the GPIO pin as an toggling output.
nrf_drv_gpiote_out_config_t config = GPIOTE_CONFIG_OUT_TASK_TOGGLE(false);
err_code = nrf_drv_gpiote_out_init(TEST_CLOCK_OUTPUT_PIN, &config);
APP_ERROR_CHECK(err_code);

// Now configure the PPI, we are going to use the the available fork mechanism (enables call of 2nd task from a single event).
err_code = nrf_drv_ppi_channel_fork_assign(tPpiChannel, nrf_drv_gpiote_out_task_addr_get(TEST_CLOCK_OUTPUT_PIN));
APP_ERROR_CHECK(err_code);

// Enable the pin for control
nrf_drv_gpiote_out_task_enable(TEST_CLOCK_OUTPUT_PIN);

The interrupt is very simple, it does a small set of calculations and then calls nrf_drv_timer_clear().

Any thoughts on why I am seeing this delay?

Cheers,

Donal

[DonalHE]

Okay, solved the problem, the call to nrf_drv_timer_clear() was not required in the interrupt. Essentially the timer was being cleared twice, which added the extra delay.