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drivers: pwm_nrfx: Wait until PWM is stopped before restarting it

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Change adds waiting until PWM is stopped before restarting it. Without
the change, calling the pwm_nrfx_pin_set function multiple times in
quick succession could cause a race condition causing the PWM to
remain stopped in case it should be restarted.

Signed-off-by: Marek Pieta <Marek.Pieta@nordicsemi.no>
This commit is contained in:
Marek Pieta 2020-03-15 20:32:02 +01:00 • committed by Carles Cufí
commit 75e36ed352
1 changed files with 18 additions and 4 deletions
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22
drivers/pwm/pwm_nrfx.c
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@ -134,6 +134,7 @@ static int pwm_nrfx_pin_set(struct device *dev, u32_t pwm,
const struct pwm_nrfx_config *config = dev->config->config_info;
struct pwm_nrfx_data *data = dev->driver_data;
u8_t channel;
bool was_stopped;
if (flags) {
/* PWM polarity not supported (yet?) */
@ -151,6 +152,14 @@ static int pwm_nrfx_pin_set(struct device *dev, u32_t pwm,
return -EINVAL;
}
/* Check if nrfx_pwm_stop function was called in previous
* pwm_nrfx_pin_set call. Relying only on state returned by
* nrfx_pwm_is_stopped may cause race condition if the pwm_nrfx_pin_set
* is called multiple times in quick succession.
*/
was_stopped = !pwm_channel_is_active(channel, data) &&
!any_other_channel_is_active(channel, data);
/* If this PWM is in center-aligned mode, pulse and period lengths
* are effectively doubled by the up-down count, so halve them here
* to compensate.
@ -223,11 +232,16 @@ static int pwm_nrfx_pin_set(struct device *dev, u32_t pwm,
* playing. The new channel values will be used
* immediately when they are written into the seq array.
*/
if (nrfx_pwm_is_stopped(&config->pwm)) {
if (was_stopped) {
/* Wait until PWM will be stopped and then start the
* sequence.
*/
while (!nrfx_pwm_is_stopped(&config->pwm)) {
};
nrfx_pwm_simple_playback(&config->pwm,
&config->seq,
1,
NRFX_PWM_FLAG_LOOP);
&config->seq,
1,
NRFX_PWM_FLAG_LOOP);
}
}