OSIntCtxSw
Description
OSIntCtxSw()
is called from OSIntExit()
to perform a context switch when all nested interrupts have returned.
Interrupts are disabled when OSIntCtxSw()
is called.
OSTCBCurPtr
points at the OS_TCB
of the task that is switched out when OSIntCtxSw()
is called and OSIntExit()
sets OSTCBHighRdyPtr
to point at the OS_TCB
of the task that is switched in.
Files
os.h/os_cpu_a.asm
Prototype
void OSIntCtxSw (void)
Arguments
None
Returned Values
None
Required Configuration
None
Callers
OSIntExit()
.
Notes/Warnings
None
Example Usage
The pseudocode for OSIntCtxSw()
is shown below. Notice that the code does only half of what OSCtxSw()
did. The reason is that OSIntCtxSw()
is called from an ISR and it is assumed that all of the CPU registers of the interrupted task were saved at the beginning of the ISR. OSIntCtxSw()
therefore must only restore the context of the new, high-priority task.
void OSIntCtxSw (void) { OSTaskSwHook(); (1) OSPrioCur = OSPrioHighRdy; (2) OSTCBCurPtr = OSTCBHighRdyPtr; (3) SP = OSTCBHighRdyPtr->StkPtr; (4) Restore all CPU registers; (5) Return from interrupt; (6) }
(1) OSIntCtxSw()
must call OSTaskSwHook()
.
(2) OSPrioHighRdy
needs to be copied to OSPrioCur
.
(3) OSTCBHighRdyPtr
needs to be copied to OSTCBCurPtr
because the current task will now be the new task.
(4) The stack pointer of the new task is restored from the OS_TCB
of the new task.
(5) All the CPU registers need to be restored from the new task’s stack.
(6) A return from interrupt instruction must be executed.