是否立即引发PendSV/SVC异常? [英] Are the PendSV / SVC exceptions raised immediately?

问题描述

我正在研究Cortex-M4上的上下文保存和还原机制，以便可以实现简单的多任务处理.我使用 arm-none-eabi-g ++ 来编译此代码.暂时不考虑可移植性.

I'm working on a context saving and restoring mechanism on the Cortex-M4 so that I can implement simple multitasking. I use arm-none-eabi-g++ for compiling this code. Portability is not a concern for now.

当任务可以调用 yield 函数时，我将其用于协作式多任务处理，这将通过引发 PendSV 异常使执行返回到内核.(然后，内核可以安排另一个任务运行，并最终返回到当前任务.)

I use this for a form of cooperative multitasking when a task can call a yield function which will make execution return to the kernel by raising a PendSV exception. (The kernel can then schedule another task for running and eventually return to the current one.)

void Task::yield() {
    // ...
    // ... (Context saving code goes here) ...
    // ...

    // Set the PENDSVSET to trigger a PendSV exception
    SCB->ICSR |= SCB_ICSR_PENDSVSET_Msk;
}

我希望执行立即返回内核.

问题是，在我将 ICSR 中的 PENDSVSET 位置1后，是否可以保证立即执行到 PendSV_Handler ?它会在 yield 函数之后继续执行指令吗?

The question is, after I set the PENDSVSET bit in the ICSR, is it guaranteed that execution goes to PendSV_Handler immediately, or does it continue executing instructions after the yield function?

为此，我最好使用 SVC 指令吗?

Would I better off using the SVC instruction for this?

void Task::yield() {
    // ...

    // SVC has an 8-bit immediate constant argument, which
    // can be used by the kernel for determining what kind
    // of system call this is.
    asm volatile("SVC 0");
}

推荐答案

从体系结构手册中的描述来看，PendSV真正用于更高优先级的异常处理程序说哦，我中断的线程是因此，现在需要在自己的上下文中进行系统调用."如果只希望线程在其正常执行过程中进行同步系统调用，则这是 svc 指令的唯一目的.

From the description in the architecture manual, PendSV is really intended for when for a higher-priority exception handler to say "oh, the thread I've interrupted is now going to need to make a system call in its own context because of this". If you simply want the thread to make a synchronous system call in the process of its normal execution, that's the sole purpose of the svc instruction.

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