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Add doxygen clarifying PWM behaviour when enabled/disabled, and advice for controlling the pin state when disabled (#521)

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Luke Wren 2021-07-19 16:21:12 +01:00 committed by GitHub
parent a6a436b1fe
commit 9a586371db
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1 changed files with 21 additions and 1 deletions
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22
src/rp2_common/hardware_pwm/include/hardware/pwm.h
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@ -441,8 +441,28 @@ static inline void pwm_set_phase_correct(uint slice_num, bool phase_correct) {
/** \brief Enable/Disable PWM
* \ingroup hardware_pwm
*
* When a PWM is disabled, it halts its counter, and the output pins are left
* high or low depending on exactly when the counter is halted. When
* re-enabled the PWM resumes immediately from where it left off.
*
* If the PWM's output pins need to be low when halted:
*
* - The counter compare can be set to zero whilst the PWM is enabled, and
* then the PWM disabled once both pins are seen to be low
*
* - The GPIO output overrides can be used to force the actual pins low
*
* - The PWM can be run for one cycle (i.e. enabled then immediately disabled)
* with a TOP of 0, count of 0 and counter compare of 0, to force the pins
* low when the PWM has already been halted. The same method can be used
* with a counter compare value of 1 to force a pin high.
*
* Note that, when disabled, the PWM can still be advanced one count at a time
* by pulsing the PH_ADV bit in its CSR. The output pins transition as though
* the PWM were enabled.
*
* \param slice_num PWM slice number
* \param enabled true to enable the specified PWM, false to disable
* \param enabled true to enable the specified PWM, false to disable.
*/
static inline void pwm_set_enabled(uint slice_num, bool enabled) {
check_slice_num_param(slice_num);