microbit: Allow passing in None to music stop/play/pitch functions.

To align with micro:bit v2 behaviour. Signed-off-by: Damien George <damien@micropython.org>

Author: dpgeorge

source/microbit/modmusic.cpp

@@ -73,17 +73,23 @@ enum {
 STATIC uint32_t start_note(const char *note_str, size_t note_len);
 
 static inline void music_output_amplitude(uint32_t amplitude) {
- pwm_set_duty_cycle(music_data->async_pin->name, amplitude);
+ if (music_data->async_pin != NULL) {
+ pwm_set_duty_cycle(music_data->async_pin->name, amplitude);
+ }
 }
 
 static inline int music_output_period_us(uint32_t period) {
  return pwm_set_period_us(period);
 }
 
 STATIC void microbit_pin_audio_select(mp_obj_t select) {
- const microbit_pin_obj_t *pin = microbit_obj_get_pin(select);
- microbit_obj_pin_acquire(pin, microbit_pin_mode_music);
- music_data->async_pin = pin;
+ if (select == mp_const_none) {
+ music_data->async_pin = NULL;
+ } else {
+ const microbit_pin_obj_t *pin = microbit_obj_get_pin(select);
+ microbit_obj_pin_acquire(pin, microbit_pin_mode_music);
+ music_data->async_pin = pin;
+ }
 }
 
 STATIC void microbit_pin_audio_free(void) {
@@ -389,13 +395,14 @@ STATIC mp_obj_t microbit_music_pitch(mp_uint_t n_args, const mp_obj_t *pos_args,
 
  bool wait = args[3].u_bool;
  music_output_amplitude(MUSIC_OUTPUT_AMPLITUDE_ON);
- if (frequency == 0) {
- pwm_release(music_data->async_pin->name);
- music_data->async_pin = NULL;
- } else if (music_output_period_us(1000000/frequency)) {
- pwm_release(music_data->async_pin->name);
- music_data->async_pin = NULL;
- mp_raise_ValueError("invalid pitch");
+ if (frequency == 0 || music_output_period_us(1000000 / frequency)) {
+ if (music_data->async_pin != NULL) {
+ pwm_release(music_data->async_pin->name);
+ music_data->async_pin = NULL;
+ }
+ if (frequency != 0) {
+ mp_raise_ValueError("invalid pitch");
+ }
  }
  if (duration >= 0) {
  // use async machinery to stop the pitch after the duration