zhuyanlinzyl opened a new pull request #5261:
URL: https://github.com/apache/incubator-nuttx/pull/5261
## Summary
Add svccall handler and use svc call in context switch.
# Reason why now context switch probability not work
In some hardware Xtensa configurations, such as we used now, all timers have
higher interrupt level than level 1.
This is not the wrong case, but when timer interrupt happen,
**the EXCM bit was not set by hardware in higher level**!!!
1) When in timer interrupt, if a context switch happen, the current
interrupted context will
save by xtensa_savestate(rtcb->xcp.regs), with **EXCM bit not set**
2) When this task become ready to run again, if it restore context from
xtensa_context_restore.
but with ps' EXCM bit not set.
after ` wsr a2, PS` instruction, the interrupt enable
again...
If interrupt happens at that time, the context was corrupted。
# Reason for use sw-interrupt as syscall interrupt
The xtensa `syscall` instruction can cause SYSCALL interrupt.
**But** syscall interrupt is same interrupt level with level-one interrupt.
It is design by hardware.
Nuttx svcall must support when `enter_critical_section` , but can generate
svcall interrupt.
# Another way
As we must find another way, we use software interrupt as svcall because:
Software interrupt may have a higher level than level-1 interrupt, this is
design by hardware configuration.
## Impact
## Testing
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