执行“执行调度函数”时，需要先对”处理机的现场信息“进行保存吗？

发布于 2015-02-03 11:38:38 浏览：2104 订阅该版

我在看操作系统原理书，书上说：”在进程调度时，首先需要保存当前进程的处理机的现场信息，如程序计数器、多个通用寄存器的内容等，将他们送入该进程的PCB中的相应单元。“
----------RT-thread需要此步骤吗？在rt_schedule()中有于此相对应的代码吗？ 代码如下：
```void rt_schedule(void)
{
    rt_base_t level;
    struct rt_thread *to_thread;
    struct rt_thread *from_thread;

/* disable interrupt */
    level = rt_hw_interrupt_disable();

/* check the scheduler is enabled or not */
    if (rt_scheduler_lock_nest == 0)
    {
        register rt_ubase_t highest_ready_priority;

#if RT_THREAD_PRIORITY_MAX <= 32
        highest_ready_priority = __rt_ffs(rt_thread_ready_priority_group) - 1;
#else
        register rt_ubase_t number;

number = __rt_ffs(rt_thread_ready_priority_group) - 1;
        highest_ready_priority = (number << 3) + __rt_ffs(rt_thread_ready_table[number]) - 1;
#endif

/* get switch to thread */
        to_thread = rt_list_entry(rt_thread_priority_table[highest_ready_priority].next,
                                  struct rt_thread,
                                  tlist);

/* if the destination thread is not the same as current thread */
        if (to_thread != rt_current_thread)
        {
            rt_current_priority = (rt_uint8_t)highest_ready_priority;
            from_thread         = rt_current_thread;
            rt_current_thread   = to_thread;

RT_OBJECT_HOOK_CALL(rt_scheduler_hook, (from_thread, to_thread));

/* switch to new thread */
            RT_DEBUG_LOG(RT_DEBUG_SCHEDULER,
                         ("[%d]switch to priority#%d "
                          "thread:%.*s(sp:0x%p), "
                          "from thread:%.*s(sp: 0x%p)
",
                          rt_interrupt_nest, highest_ready_priority,
                          RT_NAME_MAX, to_thread->name, to_thread->sp,
                          RT_NAME_MAX, from_thread->name, from_thread->sp));

#ifdef RT_USING_OVERFLOW_CHECK
            _rt_scheduler_stack_check(to_thread);
#endif

if (rt_interrupt_nest == 0)
            {
                rt_hw_context_switch((rt_uint32_t)&from_thread->sp,
                                     (rt_uint32_t)&to_thread->sp);
            }
            else
            {
                RT_DEBUG_LOG(RT_DEBUG_SCHEDULER, ("switch in interrupt
"));

rt_hw_context_switch_interrupt((rt_uint32_t)&from_thread->sp,
                                               (rt_uint32_t)&to_thread->sp);
            }
        }
    }

/* enable interrupt */
    rt_hw_interrupt_enable(level);
}```