static void
trap_dispatch(struct Trapframe *tf)
{
  // Handle processor exceptions.
  switch (tf->tf_trapno) {
        case T_PGFLT:
            page_fault_handler(tf);
            return;
        case T_BRKPT:
            monitor(tf);
            return;
        case T_SYSCALL:
            tf->tf_regs.reg_eax = syscall(tf->tf_regs.reg_eax,
                                          tf->tf_regs.reg_edx, tf->tf_regs.reg_ecx,
                                          tf->tf_regs.reg_ebx, tf->tf_regs.reg_edi,
                                          tf->tf_regs.reg_esi);
            return;
        default:
            // Unexpected trap: The user process or the kernel has a bug.
            print_trapframe(tf);
            if (tf->tf_cs == GD_KT)
                panic("unhandled trap in kernel");
            else {
                env_destroy(curenv);
                return;
            }
  }

  // Handle spurious interrupts
  // The hardware sometimes raises these because of noise on the
  // IRQ line or other reasons. We don't care.
  if (tf->tf_trapno == IRQ_OFFSET + IRQ_SPURIOUS) {
    cprintf("Spurious interrupt on irq 7\n");
    print_trapframe(tf);
    return;
  }

  // Handle clock interrupts. Don't forget to acknowledge the
  // interrupt using lapic_eoi() before calling the scheduler!
  if (tf->tf_trapno == IRQ_OFFSET + IRQ_TIMER) {
      lapic_eoi();
        sched_yield();
  }