Counting falling edges from PWM using PPI & a Timer

main.cpp

#include <zephyr.h>

#include <device.h>
#include <drivers/pwm.h>
#include <drivers/adc.h>
#include <devicetree.h>

#include <nrfx_gpiote.h>
#include <nrfx_ppi.h>
#include <nrfx_timer.h>
#include <nrfx_lpcomp.h>

// PWM will drive an LED for testing
#define OUTPUT_PIN	DT_GPIO_PIN(DT_ALIAS(led0), gpios)

// Get the alias for pwm_led0 from the device tree
#define PWM_LED0_NODE	DT_ALIAS(pwm_led0)

// Check if pwm_led0 is ok to use
#if DT_NODE_HAS_STATUS(PWM_LED0_NODE, okay)
// Get the control pin the led is attached to
#define PWM_CTLR	DT_PWMS_CTLR(PWM_LED0_NODE)
// Get the channel the led is attached to
#define PWM_CHANNEL	DT_PWMS_CHANNEL(PWM_LED0_NODE)
// Get any flags set by pwm_led in the device tree
#define PWM_FLAGS	DT_PWMS_FLAGS(PWM_LED0_NODE)
#else
#error "Unsupported board: pwm-led0 devicetree alias is not defined"
#define PWM_CTLR	DT_INVALID_NODE
#define PWM_CHANNEL	0
#define PWM_FLAGS	0
#endif

static nrfx_timer_t m_counter = NRFX_TIMER_INSTANCE(2);

static void dummy(nrfx_gpiote_pin_t pin, nrf_gpiote_polarity_t action)
{
  printk("pulse\r\n");
}

static void compare_handler(nrf_timer_event_t event_type, void* p_context)
{
  printk("compare\r\n");
  nrfx_timer_clear(&m_counter);
}

void main(void)
{
  // Welcome message
  printk("Count PWM pulses %s", CONFIG_BOARD);

  // Connect GPIOTE_0 IRQ to nrfx_gpiote_irq_handler
  IRQ_DIRECT_CONNECT(DT_IRQN(DT_NODELABEL(gpiote)), 0, nrfx_gpiote_irq_handler, 0);
  IRQ_DIRECT_CONNECT(DT_IRQN(DT_NODELABEL(timer2)), 0, nrfx_timer_2_irq_handler, 0);




  //
  // Counter setup
  //
  // Set timer as a counter
  nrfx_timer_config_t tmr_config = NRFX_TIMER_DEFAULT_CONFIG;
  tmr_config.mode = NRF_TIMER_MODE_COUNTER;
  tmr_config.bit_width = NRF_TIMER_BIT_WIDTH_32;

  // Setup timer @todo disable call back
  nrfx_timer_init(&m_counter, &tmr_config, compare_handler);
  nrfx_timer_compare(&m_counter, NRF_TIMER_CC_CHANNEL1, 100, true);

  //nrfx_timer_clear(&m_counter);
  nrfx_timer_enable(&m_counter);






  //
  // GPIOE setup
  //

  // Initialize GPIOTE
  nrfx_gpiote_init(0);

  nrfx_gpiote_in_config_t const in_config = {
      .sense = NRF_GPIOTE_POLARITY_HITOLO,
      .pull = NRF_GPIO_PIN_NOPULL,
      .is_watcher = true,
      .hi_accuracy = true,
      .skip_gpio_setup = true,
  };

  // Initialize input pin to generate event on high to low transition
  // (falling edge) and call dummy()
  nrfx_gpiote_in_init(OUTPUT_PIN, &in_config, dummy);

  // Create the event to detect
  // Leave interrupt enabled for debugging (interrupt is called)
  nrfx_gpiote_in_event_enable(OUTPUT_PIN, true);






  //
  // PPI
  //

  // Get an allocated PPI Channel
  nrf_ppi_channel_t channel_in;
  nrfx_ppi_channel_alloc(&channel_in);

  // Trigger timer count task when GPIOTE pin go from low to high.
  nrfx_ppi_channel_assign(channel_in,
                          nrfx_gpiote_in_event_addr_get(OUTPUT_PIN),
                          nrfx_timer_task_address_get(&m_counter, NRF_TIMER_TASK_COUNT)); // NRF_TIMER_TASK_CAPTURE1 NRF_TIMER_TASK_COUNT


  // Enable PII
  nrfx_ppi_channel_enable(channel_in);







  //
  // PWM Setup (@note PWM works ok, flashes LED.)
  //
  // Create an empty device structure
  const struct device *pwm;

  // Get the pwm from the pwm controller
  pwm = DEVICE_DT_GET(PWM_CTLR);

  // Check if the pwm device is ready to use
  if (!device_is_ready(pwm)) {
    printk("Error: PWM device %s is not ready\n", pwm->name);
    return;
  }

  // Try a max period of 1uS
  uint32_t max_period = 250000;

  // Slow pulse 50% duty
  pwm_pin_set_usec(pwm, PWM_CHANNEL,
                   max_period, max_period / 2U, PWM_FLAGS);

  // Program runtime
  while (1) {
    printk("value %lu", nrfx_timer_capture(&m_counter, NRF_TIMER_CC_CHANNEL0));
    // Sleep for four seconds to allow user to see the flashing change
    k_sleep(K_SECONDS(4U));
  }
}