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stm32: Improve accuracy of hardware pwm cycle time
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Use a different method of setting the hardware pwm registers so that
the actual cycle_time is much closer to the requested cycle_time.

Also, remove the now unused stm32_timer_output command, as the main
hardware pwm interface provides the same accuracy.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
This commit is contained in:
Kevin O'Connor 2026-01-02 18:37:43 -05:00
parent 8bca4cbcd9
commit e605fd1856
2 changed files with 19 additions and 40 deletions
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3
src/stm32/gpio.h
View file

@ -25,7 +25,8 @@ void gpio_in_reset(struct gpio_in g, int32_t pull_up);
uint8_t gpio_in_read(struct gpio_in g);
struct gpio_pwm {
void *reg;
void *reg;
uint32_t hwpwm_ticks;
};
struct gpio_pwm gpio_pwm_setup(uint8_t pin, uint32_t cycle_time, uint32_t val);
void gpio_pwm_write(struct gpio_pwm g, uint32_t val);

56
src/stm32/hard_pwm.c
View file

@ -11,7 +11,7 @@
#include "internal.h" // GPIO
#include "sched.h" // sched_shutdown
#define MAX_PWM 256
#define MAX_PWM (1<<15)
DECL_CONSTANT("PWM_MAX", MAX_PWM);
struct gpio_pwm_info {
@ -299,9 +299,8 @@ static const struct gpio_pwm_info pwm_regs[] = {
#endif
};
static struct gpio_pwm
gpio_timer_setup(uint8_t pin, uint32_t cycle_time, uint32_t val,
int is_clock_out)
struct gpio_pwm
gpio_pwm_setup(uint8_t pin, uint32_t cycle_time, uint32_t val)
{
// Find pin in pwm_regs table
const struct gpio_pwm_info* p = pwm_regs;
@ -322,28 +321,18 @@ gpio_timer_setup(uint8_t pin, uint32_t cycle_time, uint32_t val,
// Convert requested cycle time (cycle_time/CLOCK_FREQ) to actual
// cycle time (hwpwm_ticks*prescaler*pclock_div/CLOCK_FREQ).
uint32_t hwpwm_ticks, prescaler;
if (!is_clock_out) {
// In normal mode, allow the pulse frequency (cycle_time) to change
// in order to maintain the requested duty ratio (val/MAX_PWM).
hwpwm_ticks = MAX_PWM;
prescaler = pcycle_time / MAX_PWM;
if (prescaler > UINT16_MAX + 1)
prescaler = UINT16_MAX + 1;
else if (prescaler < 1)
prescaler = 1;
} else {
// In clock output mode, allow the pulse width enable duration
// (val) to change in order to maintain the requested frequency.
val = val / pclock_div;
hwpwm_ticks = pcycle_time;
prescaler = 1;
while (hwpwm_ticks > UINT16_MAX) {
val /= 2;
hwpwm_ticks /= 2;
prescaler *= 2;
}
uint32_t hwpwm_ticks = pcycle_time, prescaler = 1, shift = 0;
while (hwpwm_ticks > UINT16_MAX) {
shift += 1;
hwpwm_ticks = (pcycle_time + (1 << (shift-1))) >> shift;
prescaler = 1 << shift;
}
if (prescaler > UINT16_MAX + 1) {
prescaler = UINT16_MAX + 1;
hwpwm_ticks = UINT16_MAX;
}
if (hwpwm_ticks < 2)
hwpwm_ticks = 2;
// Enable requested pwm hardware block
if (!is_enabled_pclock((uint32_t) p->timer)) {
@ -364,6 +353,7 @@ gpio_timer_setup(uint8_t pin, uint32_t cycle_time, uint32_t val,
// Enable requested channel of hardware pwm block
struct gpio_pwm channel;
channel.hwpwm_ticks = hwpwm_ticks;
switch (p->channel) {
case 1: {
channel.reg = (void*) &p->timer->CCR1;
@ -419,20 +409,8 @@ gpio_timer_setup(uint8_t pin, uint32_t cycle_time, uint32_t val,
return channel;
}
struct gpio_pwm
gpio_pwm_setup(uint8_t pin, uint32_t cycle_time, uint32_t val) {
return gpio_timer_setup(pin, cycle_time, val, 0);
}
void
command_stm32_timer_output(uint32_t *args)
{
gpio_timer_setup(args[0], args[1], args[2], 1);
}
DECL_COMMAND(command_stm32_timer_output,
"stm32_timer_output pin=%u cycle_ticks=%u on_ticks=%hu");
void
gpio_pwm_write(struct gpio_pwm g, uint32_t val) {
*(volatile uint32_t*) g.reg = val;
uint32_t r = DIV_ROUND_CLOSEST(val * g.hwpwm_ticks, MAX_PWM);
*(volatile uint32_t*) g.reg = r;
}