Hi everyone, hitting a strange issue that I cant seem to figure out. Hope this isnt too arch specific…
I have created a basic application which is setting up a timer that will flash an LED once the device has “booted” and is running.
But when running my code, it ends up crashing with a reserved instruction exception, according to the CAUSE register.
The EPC register contains an address of 0x9D00803C, and when I look at this code in the disassembly I get a jump instruction:
portYIELD_WITHIN_API();
9d00801c: 40026800 mfc0 v0,c0_cause
9d008020: afc20014 sw v0,20(s8)
9d008024: 8fc20014 lw v0,20(s8)
9d008028: 34420100 ori v0,v0,0x100
9d00802c: afc20014 sw v0,20(s8)
9d008030: 8fc20014 lw v0,20(s8)
9d008034: 40826800 mtc0 v0,c0_cause
9d008038: 000000c0 ehb
9d00803c <.LBE2>:
9d00803c: 0b402013 j 9d00804c <.LVL84>
9d008040: 00000000 nop
}
}
}
else
{
( void ) xTaskResumeAll();
9d008044: 0f4011f3 jal 9d0047cc <xTaskResumeAll>
9d008048: 00000000 nop
Im using kernel 10.4.1, and the above code would seem to correspond to https://github.com/FreeRTOS/FreeRTOS-Kernel/blob/V10.4.1-kernel-only/timers.c#L633
Im seeing a little bit of conflicting information about the EPC register, some sources say that it is the return address (i.e. where execution would resume from), and other sources seem to imply that it will hold the address of the instruction that caused the exception (or the address of the JUMP instruction if the exception happened in the branch slot).
I think it is related to the EHB instruction, because if I add a NOP after EHB and before the JUMP, the EPC address changes to the NOP instruction.
Wondering if anyone could provide any pointers where I should look or things I should try to resolve this?
Thanks
