Function attach_timer_handler

src/platforms/arm/samd/isr_samd.hpp:369–523

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

int attach_timer_handler(const isr_config_t& config, isr_handle_t* out_handle) FL_NOEXCEPT {
    if (!config.handler) {
        FL_WARN("attachTimerHandler: handler is null");
        return -1;  // Invalid parameter
    }

    if (config.frequency_hz == 0) {
        FL_WARN("attachTimerHandler: frequency_hz is 0");
        return -2;  // Invalid frequency
    }

    // Allocate a free timer
    u8 timer_idx = 0;
    if (!allocate_timer(timer_idx)) {
        FL_WARN("attachTimerHandler: no free timers");
        return -3;  // Out of resources
    }

    Tc* timer = get_timer_instance(timer_idx);
    if (!timer) {
        free_timer(timer_idx);
        FL_WARN("attachTimerHandler: invalid timer instance");
        return -4;  // Internal error
    }

    // Allocate handle data
    auto handle_owner = fl::make_unique<samd_isr_handle_data>();
    auto* handle_data = handle_owner.get();
    if (!handle_data) {
        free_timer(timer_idx);
        FL_WARN("attachTimerHandler: failed to allocate handle data");
        return -5;  // Out of memory
    }

    handle_data->is_timer = true;
    handle_data->timer_instance = timer;
    handle_data->timer_index = timer_idx;
    handle_data->timer_irq = get_timer_irq(timer_idx);
    handle_data->user_handler = config.handler;
    handle_data->user_data = config.user_data;

    // Store handle for ISR access
    timer_handles[timer_idx] = handle_data;

    // Enable clock for timer
#if defined(FL_IS_SAMD21)
    // SAMD21: Use GCLK to route clock to TC peripheral
    // Most SAMD21 boards use GCLK_CLKCTRL_ID_TCC2_TC3 for TC3/TC4/TC5
    u16 gclk_id;
    if (timer_idx <= 5) {
        gclk_id = GCLK_CLKCTRL_ID_TCC2_TC3;
    } else {
        gclk_id = GCLK_CLKCTRL_ID_TCC2_TC3;  // Adjust if TC6/TC7 available
    }

    GCLK->CLKCTRL.reg = (u16)(GCLK_CLKCTRL_CLKEN | GCLK_CLKCTRL_GEN_GCLK0 | gclk_id);
    while (GCLK->STATUS.bit.SYNCBUSY) {
        // Wait for sync