Fix for issue #4937 - Implement minimum PulseOut time

ports/raspberrypi/common-hal/pulseio/PulseOut.c

@@ -43,22 +43,33 @@ static volatile uint16_t pulse_index = 0;
 static uint16_t pulse_length;
 pwmio_pwmout_obj_t *pwmout_obj;
 volatile uint16_t current_duty_cycle;
+static uint32_t min_pulse = 0;
+static alarm_id_t cur_alarm;
 
-void pulse_finish(void) {
+void pulse_finish(pwmio_pwmout_obj_t *carrier) {
     pulse_index++;
     // Turn pwm pin off by setting duty cyle to 1.
-    common_hal_pwmio_pwmout_set_duty_cycle(pwmout_obj,1);
+    common_hal_pwmio_pwmout_set_duty_cycle(carrier,1);
     if (pulse_index >= pulse_length) {
         return;
     }
-    add_alarm_in_us(pulse_buffer[pulse_index], pulseout_interrupt_handler, NULL, false);
     if (pulse_index % 2 == 0) {
-        common_hal_pwmio_pwmout_set_duty_cycle(pwmout_obj,current_duty_cycle);
+        common_hal_pwmio_pwmout_set_duty_cycle(carrier,current_duty_cycle);
+    }
+    uint64_t delay = pulse_buffer[pulse_index];
+    if (delay < min_pulse) {
+        delay = min_pulse;
+    }
+    cur_alarm = 0;
+    // if the alarm cannot be set, try again with a longer delay
+    while (cur_alarm == 0) {
+        cur_alarm = add_alarm_in_us(delay, pulseout_interrupt_handler, carrier, false);
+        delay = delay + 1;
     }
 }
 
 int64_t pulseout_interrupt_handler(alarm_id_t id, void *user_data) {
-    pulse_finish();
+    pulse_finish(user_data);
     return 0;
 }
 
@@ -75,9 +86,12 @@ void common_hal_pulseio_pulseout_construct(pulseio_pulseout_obj_t *self,
     refcount++;
     pwmout_obj = (pwmio_pwmout_obj_t *)carrier;
     current_duty_cycle = common_hal_pwmio_pwmout_get_duty_cycle(pwmout_obj);
+    pwm_set_enabled(carrier->slice,false);
+    common_hal_pwmio_pwmout_set_duty_cycle(pwmout_obj,1);
     self->pin = carrier->pin->number;
     self->slice = carrier->slice;
-    pwm_set_enabled(pwmout_obj->slice,false);
+    self->carrier = pwmout_obj;
+    min_pulse = (1000000 / carrier->actual_frequency);
 }
 
 bool common_hal_pulseio_pulseout_deinited(pulseio_pulseout_obj_t *self) {
@@ -97,16 +111,26 @@ void common_hal_pulseio_pulseout_send(pulseio_pulseout_obj_t *self, uint16_t *pu
     pulse_index = 0;
     pulse_length = length;
 
-    add_alarm_in_us(pulses[0], pulseout_interrupt_handler, NULL, false);
-    common_hal_pwmio_pwmout_set_duty_cycle(pwmout_obj,current_duty_cycle);
-    pwm_set_enabled(pwmout_obj->slice,true);
+    common_hal_pwmio_pwmout_set_duty_cycle(self->carrier,current_duty_cycle);
+    pwm_set_enabled(self->slice,true);
+    uint64_t delay = pulse_buffer[0];
+    if (delay < min_pulse) {
+        delay = min_pulse;
+    }
+    alarm_id_t init_alarm = 0;
+    // if the alarm cannot be set, try again with a longer delay
+    while (init_alarm == 0) {
+        init_alarm = add_alarm_in_us(delay, pulseout_interrupt_handler, self->carrier, false);
+        delay = delay + 1;
+    }
+    cur_alarm = init_alarm;
 
     while (pulse_index < length) {
         // Do other things while we wait. The interrupts will handle sending the
         // signal.
         RUN_BACKGROUND_TASKS;
     }
     // Short delay to give pin time to settle before disabling PWM
-    common_hal_mcu_delay_us(25);
-    pwm_set_enabled(pwmout_obj->slice,false);
+    common_hal_mcu_delay_us(min_pulse);
+    pwm_set_enabled(self->slice,false);
 }

ports/raspberrypi/common-hal/pulseio/PulseOut.h

@@ -28,6 +28,7 @@
 #define MICROPY_INCLUDED_ATMEL_SAMD_COMMON_HAL_PULSEIO_PULSEOUT_H
 
 #include "common-hal/microcontroller/Pin.h"
+#include "common-hal/pwmio/PWMOut.h"
 #include "src/common/pico_time/include/pico/time.h"
 
 #include "py/obj.h"
@@ -38,9 +39,10 @@ typedef struct {
     mp_obj_base_t base;
     uint8_t pin;
     uint8_t slice;
+    pwmio_pwmout_obj_t *carrier;
 } pulseio_pulseout_obj_t;
 
 void pulseout_reset(void);
 int64_t pulseout_interrupt_handler(alarm_id_t id, void *user_data);
 
-#endif // MICROPY_INCLUDED_ATMEL_SAMD_COMMON_HAL_PULSEIO_PULSEOUT_H
+#endif // MICROPY_INCLUDED_ATMEL SAMD_COMMON_HAL_PULSEIO_PULSEOUT_H