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RP2040: fix off-by-one PWM top issue #4192

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merged 2 commits into from
Feb 17, 2021
Merged

RP2040: fix off-by-one PWM top issue #4192

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3e43281
fix off-by-one PWM top issue
dhalbert Feb 12, 2021
0ec99b3
handle 100% duty cycle; improve actual_frequency calc
dhalbert Feb 13, 2021
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42 changes: 32 additions & 10 deletions ports/raspberrypi/common-hal/pwmio/PWMOut.c
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Original file line number Diff line number Diff line change
Expand Up @@ -45,6 +45,18 @@ uint32_t slice_variable_frequency;
static uint32_t channel_use;
static uint32_t never_reset_channel;

// Per the RP2040 datasheet:
//
// "A CC value of 0 will produce a 0% output, i.e. the output signal
// is always low. A CC value of TOP + 1 (i.e. equal to the period, in
// non-phase-correct mode) will produce a 100% output. For example, if
// TOP is programmed to 254, the counter will have a period of 255
// cycles, and CC values in the range of 0 to 255 inclusive will
// produce duty cycles in the range 0% to 100% inclusive."
//
// So 65534 should be the maximum top value, and we'll set CC to be TOP+1 as appropriate.
#define MAX_TOP 65534

static uint32_t _mask(uint8_t slice, uint8_t channel) {
return 1 << (slice * CHANNELS_PER_SLICE + channel);
}
Expand Down Expand Up @@ -164,19 +176,28 @@ void common_hal_pwmio_pwmout_deinit(pwmio_pwmout_obj_t* self) {

extern void common_hal_pwmio_pwmout_set_duty_cycle(pwmio_pwmout_obj_t* self, uint16_t duty) {
self->duty_cycle = duty;
uint16_t actual_duty = duty * self->top / ((1 << 16) - 1);
pwm_set_chan_level(self->slice, self->channel, actual_duty);
// Do arithmetic in 32 bits to prevent overflow.
uint16_t compare_count;
if (duty == 65535) {
// Ensure that 100% duty cycle is 100% full on and not rounded down,
// but do MIN() to keep value in range, just in case.
compare_count = MIN(UINT16_MAX, (uint32_t) self->top + 1);
} else {
compare_count= ((uint32_t) duty * self->top + MAX_TOP / 2) / MAX_TOP;
}
// compare_count is the CC register value, which should be TOP+1 for 100% duty cycle.
pwm_set_chan_level(self->slice, self->channel, compare_count);
}

uint16_t common_hal_pwmio_pwmout_get_duty_cycle(pwmio_pwmout_obj_t* self) {
return self->duty_cycle;
}

void pwmio_pwmout_set_top(pwmio_pwmout_obj_t* self, uint32_t top) {
void pwmio_pwmout_set_top(pwmio_pwmout_obj_t* self, uint16_t top) {
self->actual_frequency = common_hal_mcu_processor_get_frequency() / top;
self->top = top;
pwm_set_clkdiv_int_frac(self->slice, 1, 0);
pwm_set_wrap(self->slice, self->top - 1);
pwm_set_wrap(self->slice, self->top);
}

void common_hal_pwmio_pwmout_set_frequency(pwmio_pwmout_obj_t* self, uint32_t frequency) {
Expand All @@ -187,7 +208,7 @@ void common_hal_pwmio_pwmout_set_frequency(pwmio_pwmout_obj_t* self, uint32_t fr
target_slice_frequencies[self->slice] = frequency;

// For low frequencies use the divider to give us full resolution duty_cycle.
if (frequency < (common_hal_mcu_processor_get_frequency() / (1 << 16))) {
if (frequency <= (common_hal_mcu_processor_get_frequency() / (1 << 16))) {
// Compute the divisor. It's an 8 bit integer and 4 bit fraction. Therefore,
// we compute everything * 16 for the fractional part.
// This is 1 << 12 because 4 bits are the * 16.
Expand All @@ -201,16 +222,17 @@ void common_hal_pwmio_pwmout_set_frequency(pwmio_pwmout_obj_t* self, uint32_t fr
if (div16 >= (1 << 12)) {
div16 = (1 << 12) - 1;
}
self->actual_frequency = frequency16 / div16;
self->top = 1 << 16;
self->actual_frequency = (frequency16 + (div16 / 2)) / div16;
self->top = MAX_TOP;
pwm_set_clkdiv_int_frac(self->slice, div16 / 16, div16 % 16);
pwm_set_wrap(self->slice, self->top - 1);
pwm_set_wrap(self->slice, self->top);
} else {
uint32_t top = common_hal_mcu_processor_get_frequency() / frequency;
self->actual_frequency = common_hal_mcu_processor_get_frequency() / top;
self->top = top;
self->top = MIN(MAX_TOP, top);
pwm_set_clkdiv_int_frac(self->slice, 1, 0);
pwm_set_wrap(self->slice, self->top - 1);
// Set TOP register. For 100% duty cycle, CC must be set to TOP+1.
pwm_set_wrap(self->slice, self->top);
}
common_hal_pwmio_pwmout_set_duty_cycle(self, self->duty_cycle);
}
Expand Down
4 changes: 2 additions & 2 deletions ports/raspberrypi/common-hal/pwmio/PWMOut.h
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Expand Up @@ -39,11 +39,11 @@ typedef struct {
bool variable_frequency;
uint16_t duty_cycle;
uint32_t actual_frequency;
uint32_t top;
uint16_t top;
} pwmio_pwmout_obj_t;

void pwmout_reset(void);
// Private API for AudioPWMOut.
void pwmio_pwmout_set_top(pwmio_pwmout_obj_t* self, uint32_t top);
void pwmio_pwmout_set_top(pwmio_pwmout_obj_t* self, uint16_t top);

#endif // MICROPY_INCLUDED_ATMEL_SAMD_COMMON_HAL_PWMIO_PWMOUT_H
1 change: 0 additions & 1 deletion shared-bindings/adafruit_bus_device/SPIDevice.c
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Expand Up @@ -34,7 +34,6 @@

#include "lib/utils/buffer_helper.h"
#include "lib/utils/context_manager_helpers.h"
#include "py/objproperty.h"
#include "py/runtime.h"
#include "supervisor/shared/translate.h"

Expand Down