Low-power PWM library: PWM doesnt stop if low_power_pwm_stop is called from handler. Is this a bug?

[Prasad]

I am using SDK 12.0.0.

I am working with low_power_pwm_init() to initialise the pwm and I have passed a handler while initialising. I want to stop the pwm from the handler hence I am calling low_power_pwm_stop() from the handler. I observe that the pwm doesnt stop.

I tried to investigate the reason for this and found that pwm_timeout_handler() in low_power_pwm.c is restarting the pwm. Below is the snippet that is suspect.

if (p_pwm_instance->pwm_state == NRF_DRV_STATE_INITIALIZED)
{
    p_pwm_instance->pwm_state = NRF_DRV_STATE_POWERED_ON;
    err_code = app_timer_start(*p_pwm_instance->p_timer_id, p_pwm_instance->timeout_ticks, p_pwm_instance);
    APP_ERROR_CHECK(err_code);
}

In low_power_pwm_stop(), p_pwm_instance->pwm_state is assigned NRF_DRV_STATE_INITIALIZED and in the above snippet the timer is started if the driver state is NRF_DRV_STATE_INITIALIZED, causing the pwm to be ON again.

Is this a bug?

[Ole Bauck]

Hi,

I can see that this will be the case and will report it internally.

You can set a flag in the event handler and call the stop routine in main.

Ole

[FormerMember]

I modified the low_power_pwm.c to fix.

static void pwm_timeout_handler(void * p_context)
{
    ret_code_t err_code;
    uint8_t duty_cycle;

    low_power_pwm_t * p_pwm_instance = (low_power_pwm_t *)p_context;

    if (p_pwm_instance->evt_type == LOW_POWER_PWM_EVENT_PERIOD)
    {
        duty_cycle = p_pwm_instance->duty_cycle;

        if (duty_cycle == p_pwm_instance->period)    // Process duty cycle 100%
        {
            led_on(p_pwm_instance);
            p_pwm_instance->timeout_ticks = p_pwm_instance->period + APP_TIMER_MIN_TIMEOUT_TICKS;
        }
        else if (duty_cycle == 0)   // Process duty cycle 0%
        {
            led_off(p_pwm_instance);
            p_pwm_instance->timeout_ticks = p_pwm_instance->period + APP_TIMER_MIN_TIMEOUT_TICKS;
        }
        else // Process any other duty cycle than 0 or 100%
        {
            led_on(p_pwm_instance);
            p_pwm_instance->timeout_ticks = ((duty_cycle * p_pwm_instance->period)>>8) +
                                APP_TIMER_MIN_TIMEOUT_TICKS;
            // setting next state
            p_pwm_instance->evt_type = LOW_POWER_PWM_EVENT_DUTY_CYCLE;
        }

        if (p_pwm_instance->handler)
        {
            p_pwm_instance->handler(p_pwm_instance);
        }
    }
    else
    {
        led_off(p_pwm_instance);
        p_pwm_instance->evt_type = LOW_POWER_PWM_EVENT_PERIOD;
        p_pwm_instance->timeout_ticks = (((p_pwm_instance->period - p_pwm_instance->duty_cycle) * p_pwm_instance->period)>>8) +
                                  APP_TIMER_MIN_TIMEOUT_TICKS;
    }

    if (p_pwm_instance->pwm_state == NRF_DRV_STATE_POWERED_ON)
    {
        err_code = app_timer_start(*p_pwm_instance->p_timer_id, p_pwm_instance->timeout_ticks, p_pwm_instance);
        APP_ERROR_CHECK(err_code);
    }
}

I hope it helps you.