I am trying to implement frequency counting on nRF51822 by counting number of pulses in a given period. I create a PPI channel with a GPIOTE event on rising edge linked to TIMER counting task. The relevant code is as follows:
#define USE_WITH_SOFTDEVICE 1
#define FC_GPIO 2
#define FC_TIMER NRF_TIMER0
#define FC_GPIOTE_CH 0
#define FC_PPI_CH 0
static void ppi_enable_channel(uint32_t ch_num, volatile uint32_t *event_ptr, volatile uint32_t *task_ptr)
{
if(ch_num >= 16) return;
else
{
#if(USE_WITH_SOFTDEVICE == 1)
sd_ppi_channel_assign(ch_num, event_ptr, task_ptr);
sd_ppi_channel_enable_set(1 << ch_num);
#else
// Otherwise we configure the channel and return the channel number
NRF_PPI->CH[ch_num].EEP = (uint32_t)event_ptr;
NRF_PPI->CH[ch_num].TEP = (uint32_t)task_ptr;
NRF_PPI->CHENSET = (1 << ch_num);
#endif
}
}
// Create a PPI channel: GPIOTE event from low to high --> FC_TIMER count up by 1
static void counting_init(void)
{
nrf_gpio_cfg_input(FC_GPIO, NRF_GPIO_PIN_NOPULL); // frequency counting input
// Init timer
FC_TIMER->TASKS_CLEAR = 1;
FC_TIMER->BITMODE = TIMER_BITMODE_BITMODE_16Bit;
FC_TIMER->MODE = TIMER_MODE_MODE_Counter;
FC_TIMER->PRESCALER = 0;
FC_TIMER->TASKS_CAPTURE[0] = 0;
// Init GPIOTE
nrf_gpiote_event_config(FC_GPIOTE_CH, FC_GPIO, NRF_GPIOTE_POLARITY_LOTOHI);
// enable PPI
ppi_enable_channel(FC_PPI_CH, &NRF_GPIOTE->EVENTS_IN[FC_GPIOTE_CH], &FC_TIMER->TASKS_COUNT);
}
// Destructor
static void counting_deinit(void)
{
FC_TIMER->TASKS_STOP = 1;
FC_TIMER->TASKS_SHUTDOWN = 1;
nrf_gpiote_unconfig(FC_GPIOTE_CH);
nrf_gpio_cfg_output(FC_GPIO);
nrf_gpio_pin_clear(FC_GPIO);
}
static uint16_t count_get(void)
{
uint16_t count;
counting_init();
FC_TIMER->TASKS_START = 1;
nrf_delay_ms(1); // try busy wait
FC_TIMER->TASKS_CAPTURE[0] = 1;
count = FC_TIMER->CC[0];
counting_deinit();
return count;
}
The last function count_get() returns the number of counts. However, when I call the function in the code, the program results in hard default. If I don't call the function, the code runs fine. So there should be something wrong with the way I implement in. Please advise.
