A simple x86_64 microkernel
for educational study.

void ipc_send(task_t *sender, int target_tid, const char *msg, size_t len) {
    task_t *target = &tasks[target_tid];
    
    // Block sender until mailbox is empty (Synchronization)
    while (target->mailbox.occupied) {
        sender->state = TASK_BLOCKED;
        sched_yield();
    }
    
    // Copy message to target's mailbox
    memcpy(target->mailbox.buffer, msg, len);
    target->mailbox.occupied = true;
    
    // Wake receiver if it was waiting
    if (target->state == TASK_BLOCKED) {
        target->state = TASK_READY;
    }
}

task_t* pick_next_task() {
    // Simple Round-Robin Scheduler
    for (int i = 0; i < MAX_TASKS; i++) {
        current_task_idx = (current_task_idx + 1) % MAX_TASKS;
        task_t *t = &tasks[current_task_idx];
        
        if (t->state == TASK_READY) {
            t->state = TASK_RUNNING;
            return t;
        }
    }
    return &idle_task;
}

void syscall_handler(uint64_t syscall_num, ...) {
    // Fast SYSCALL instruction entry point
    switch (syscall_num) {
        case SYS_WRITE:
            sys_write(arg1, arg2, arg3);
            break;
        case SYS_SEND:
            sys_send(arg1, arg2, arg3);
            break;
        case SYS_YIELD:
            sched_yield();
            break;
    }
}