Timer0 interrupt only firing once on nRF52832 using nrfx sdk - how to re-enable in ISR?

[Matt_V]

Hi,

With the attached code, the timer0_event_handler() is only called once - is there something else I need to do in the ISR or at initialisation-time to ensure that it fires repeatedly?   

#define NRFX_PPI_ENABLED 1

#include "sdk_config.h"
#include "nrf52.h"
#include "system_nrf52.h"

#define PIN_RED_LED   14
#define PIN_GREEN_LED 16
#define PIN_BLUE_LED  15


#include <stdint.h>
#include "app_error.h"

#include "nrfx_gpiote.h"
#include "nrfx_ppi.h"
#include "nrfx_clock.h"
#include "nrfx_rtc.h"
#include "nrfx_timer.h"

#include "nrf_log.h"
#include "nrf_log_ctrl.h"
#include "nrf_log_default_backends.h"

#define TIMER0_INTERVAL             (1000)  // Timer interval in milliseconds
#define TIMER1_INTERVAL             (2000)  // Timer interval in milliseconds
#define TIMER2_INTERVAL             (2000)  // Timer interval in milliseconds


static const nrfx_rtc_t m_rtc0 = NRFX_RTC_INSTANCE(0);

static const nrfx_timer_t m_timer0 = NRFX_TIMER_INSTANCE(0);
static const nrfx_timer_t m_timer1 = NRFX_TIMER_INSTANCE(1);
static const nrfx_timer_t m_timer2 = NRFX_TIMER_INSTANCE(2);

static nrf_ppi_channel_t m_ppi_channel1;
static nrf_ppi_channel_t m_ppi_channel2;

static volatile uint32_t m_counter;

static void timer0_event_handler(nrf_timer_event_t event_type, void * p_context)
{
   static uint32_t state = 0;

   nrfx_timer_clear(&m_timer0);
   nrfx_timer_enable(&m_timer0);
...
}

...

/** @brief Function for Timer 0 initialization.
 *  @details It is configured to generate an interrupt every 1000ms.
 */
static void timer0_init(void)
{
    // Check TIMER0 configuration for details.
    nrfx_timer_config_t timer_cfg = NRFX_TIMER_DEFAULT_CONFIG;
    timer_cfg.frequency = NRF_TIMER_FREQ_4MHz;
    ret_code_t err_code = nrfx_timer_init(&m_timer0, &timer_cfg, timer0_event_handler);
    APP_ERROR_CHECK(err_code);

    nrfx_timer_extended_compare(&m_timer0,
                                NRF_TIMER_CC_CHANNEL0,
                                nrfx_timer_ms_to_ticks(&m_timer0,
                                                       TIMER0_INTERVAL),
                                NRF_TIMER_SHORT_COMPARE0_CLEAR_MASK,
                                true);
}

...

int main(void)
{
   SystemInit();
...
   timer0_init();

[hmolesworth]

Don't need the isr as the SHORTS handles the clear and leaves timer running, try getting rid of it:

    ret_code_t err_code = nrfx_timer_init(&m_timer0, &timer_cfg, NULL); <<==
    APP_ERROR_CHECK(err_code);

    nrfx_timer_extended_compare(&m_timer0,
                                NRF_TIMER_CC_CHANNEL0,
                                nrfx_timer_ms_to_ticks(&m_timer0,
                                                       TIMER0_INTERVAL),
                                NRF_TIMER_SHORT_COMPARE0_CLEAR_MASK,
                                false);   <<==

[Matt_V]

I need the ISR to perform an application specific action though.  What's SHORTS, btw?  

[hmolesworth]

SHORTS as set in the code above clears the timer on compare 0 and leaves it running so isr shouldn't redundantly clear or attempt to enable; if the isr is required simply do this:

static void timer0_event_handler(nrf_timer_event_t event_type, void * p_context)
{
   static uint32_t state = 0;

//   nrfx_timer_clear(&m_timer0);
//   nrfx_timer_enable(&m_timer0);
...
}

[Matt_V]

I do need to do app-specific things in the ISR though (I've just left them out of the code I posted, for conciseness and confidentiality) .  

The lines:
nrfx_timer_clear(&m_timer0);
nrfx_timer_enable(&m_timer0);
I only added these two lines when the ISR failed to work more than once initially - but this didn't help.