[Scheduler] Scheduler crashes after some time

[trylimits]

The scheduler crashes after some time (atm it crashes after one hour). I assume this is caused by not restoring the stack pointer after a context switch, however, we should investigate the problem if it causes major issues.

[trylimits]

See initial Bug #28 for more information

[ghost]

I think I found the problem. I'll write you later.

[trylimits]

From Bug #28 @mpe5651

Take a look at the last line in the restore registers function:

RestoreRegisters:

ADD SP, SP, #40
LDMFD SP!, {CPSR}
LDMFD    SP, {R13}^
NOP
ADD      SP, SP, #4
;LDMFD   SP!, {SP}
LDMFD    SP, {R0-R12, PC}^
;ADD         SP, SP, #56

We are restoring the registers without correcting the stack pointer. Then the relative slow crash after about an hour would make sense. What do you think? I'm sorry that I can't test it, I'm currently not st home.

[trylimits]

I think you are right but the problem is a little bit difficult to solve. The last line restores the context including the PC, thus we cannot do anything below that line. Let's discuss that issue in the next coaching.

[ghost]

Ok. But I would like to invest about 10 minutes tomorrow and test the following sequence:

LDMFD    SP, {R0-R12}^
ADD         SP, SP, #52 
LDMFD    SP, {LR}^
ADD         SP, SP, #4
SUBS        PC, LR, #4

[trylimits]

@mpe5651 Implemented the suggested fix. Further testing needed, but looks good.

[trylimits]

Commit has not changed the behaviour.

[trylimits]

Introducing the MMU has fixed this problem. Therefore closing this issue.