Function setPwmFrequency

src/fl/system/pin.cpp.hpp:274–352

// ============================================================================

int setPwmFrequency(int pin, u32 frequency_hz) {
    // Check if pin already has a channel
    pwm_state::PwmPinState* ch = pwm_state::findByPin(pin);

    if (ch) {
        // Pin already configured — release and reconfigure
        pwm_state::releaseChannel(ch);
        ch = nullptr;
    }

    // Validate frequency
    if (frequency_hz == 0) {
        FL_WARN("setPwmFrequency: Frequency must be > 0");
        return -1;
    }

    // Query platform: can it handle this natively?
    bool needs_isr = platforms::needsPwmIsrFallback(pin, frequency_hz);

    if (!needs_isr) {
        // Native path
        int result = platforms::setPwmFrequencyNative(pin, frequency_hz);
        if (result != 0) {
            FL_WARN("setPwmFrequency: Native backend failed: " << result);
            return result;
        }

        // Allocate tracking slot
        ch = pwm_state::allocate();
        if (!ch) {
            FL_WARN("setPwmFrequency: All " << static_cast<int>(pwm_state::MAX_PWM_CHANNELS) << " channels in use");
            return -2;
        }

        ch->pin = pin;
        ch->frequency_hz = frequency_hz;
        ch->backend = pwm_state::PwmBackend::Native;
        ch->duty_cycle = 0;
        return 0;
    }

    // ISR software fallback path
    if (frequency_hz > pwm_state::MAX_ISR_PWM_FREQUENCY) {
        FL_WARN("setPwmFrequency: ISR fallback max " << pwm_state::MAX_ISR_PWM_FREQUENCY << " Hz, requested " << frequency_hz);
        return -1;
    }

    // Allocate channel
    ch = pwm_state::allocate();
    if (!ch) {
        FL_WARN("setPwmFrequency: All " << static_cast<int>(pwm_state::MAX_PWM_CHANNELS) << " channels in use");
        return -2;
    }

    // Ensure ISR is running
    int isr_result = pwm_state::ensureIsrActive();
    if (isr_result != 0) {
        return -3;