How does context switching work?

[Sebastian Huber]

On 31/10/2020 16:50, Richi Dubey wrote:

>
> I want to learn more about how context switching works in RTEMS. I saw 
> the following lines in theaddispatch.c:
>
>     _Thread_Save_fp( executing );
>     _Context_Switch( &executing->Registers, &heir->Registers );
>     _Thread_Restore_fp( executing );
>
> I do not understand how it works. Here, the executing process saves 
> its context by calling _Thread_Save_fp( executing ), then if a 
> different process resumes execution after the context switch, why does 
> it get the context of previous process (executing)?
The _Context_Switch() function changes the thread stack and the 
non-volatile (callee save) registers. So, the value of the executing 
local variable changes with a call to _Context_Switch().

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Sebastian Huber, embedded brains GmbH

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