Hi Elvin,
It might be a bit easier to understand with the comments left in:
if (old_tcb != new_tcb)
{
/* Set the new currently-running thread pointer */
curr_tcb = new_tcb;
/* Call the architecture-specific context switch */
archContextSwitch (old_tcb, new_tcb);
}
/**
* The context switch shifted execution to a different thread. By the time
* we get back here, we are running in old_tcb context again. Clear its
* suspend status now that we're back.
*/
old_tcb->suspended = FALSE;
The suspended flag is set to TRUE when a thread is being suspended,
and is set to FALSE when it runs again. This is used as housekeeping,
to keep a track of what suspension state a thread is in.
For any thread that calls into this function, the calling thread
(itself) is old_tcb and the new thread being switched in is new_tcb.
When you return from archContextSwitch() *in the context of the
original calling thread* then the running thread is back to the
original thread (old_tcb), so it needs to mark itself as not suspended
any more, by setting its flag to FALSE again.
Thanks,
Kelvin.
On 11 September 2012 12:29, elvinwds <elvin...@gmail.com> wrote:
> Hi All:
>
> I am a new to RTOS and have been studying the source code of atomthreads
> for a while, and now I have question about the atomThreadSwitch function in
> atomkernel.c.
>
> The source code without comments of atomThreadSwitch is :
> static void atomThreadSwitch(ATOM_TCB *old_tcb, ATOM_TCB *new_tcb)
> {
> if (old_tcb != new_tcb)
> {
> /* Set the new currently-running thread pointer */
> curr_tcb = new_tcb;
>
> /* Call the architecture-specific context switch */
> archContextSwitch (old_tcb, new_tcb);
> }
>
> old_tcb->suspended = FALSE;
>
> }
>
> My question is about the last line : "old_tcb->suspended = FALSE". Only
> when the old thread been scheduled back in, the RTOS can run to here. This
> means that when the RTOS runs to here , the old thread has been scheduled
> out, so the state of the old thread can not be suspended, And why have to
> set the state of suspended false here?
>
>
> With Regards,
> Elvin
