soft-pwm v0.1.0

Software PWM on a single pin, driven by a fixed tick.

Application scenarios

• An LED or heater on a low-end MCU with no spare hardware PWM.
• A fan or solenoid that needs a slow duty cycle.
• A status LED that must share a timer with other work.

Contract

typedef struct {
    void *context;
    void (*set)(void *context, uint8_t level);
} soft_pwm_port_t;

void soft_pwm_init(soft_pwm_t *pwm, soft_pwm_port_t port, uint16_t period);
void soft_pwm_set_duty(soft_pwm_t *pwm, uint16_t duty);
void soft_pwm_tick(soft_pwm_t *pwm);

• Call soft_pwm_tick at a fixed rate; period is the number of ticks.
• Duty is clamped to 0..period.
• period = 0 becomes 1.
• No allocation.

Parameters

• Tick rate / period sets the PWM frequency; keep it above visible flicker

for LEDs (>= 100 Hz) and below the actuator's response limit.

• Duty resolution is 1/period.

Memory and timing

• 12 bytes of state plus the port context.
• O(1) per tick; one pin write.

Integration

soft_pwm_t led;
soft_pwm_init(&led, board_led_port(), 100);
soft_pwm_set_duty(&led, 25);
/* every 100 us: */ soft_pwm_tick(&led);

Adapters

• Keep the pin write and timer setup in the adapter.
• Reference: Padauk PWM/LED examples; CA51 low-end projects.
• Prefer hardware PWM when a channel is free.

When not to use

• High frequency or low jitter is required; use a hardware timer.
• The tick is not periodic; the duty will drift.

Verification

make test covers the 0/50/100% duty sequence, clamping, and period zero.

void *context;
void (*set)(void *context, uint8_t level);