ColdFire/68K Microcontrollers and ProcessorsのトピックRe: simple assembly "illegal instruction" exception handler

simple assembly "illegal instruction" exception handler

order324 — Thu, 26 Mar 2009 03:46:58 GMT

Any one have a simple assembly "illegal instruction" exception handler that allows the program to continue after skipping over the illegal instruction? Here is what I have so far (it executes the routine but the routine doesn't work):

DEBUG_EXC_HANDLER:

        move.l #0x00000001,%D0 || put 1 in D0
        add.l %D0,%D3          || add D0 to D3 and put the result in D3

                                      ||(simple counter so I can see what's happening)
        nop
        nop

        move.l (%A7)+,%D7 || pop status off stack
        move.l (%A7)+,%D7 || pop pc off stack

        move.l #0x00000002,%D1
        move.l %D7,%D0
        add.l %D1,%D0          || add D1 to D0 and put the result in D0
        move.l %D0,-(%A7)      || set top of stack to be error pc+2

        nop
        nop

        rte

        nop
        nop

|| end

With this handler, I get a "format error" exception (different exception) right after the rte. Clearly I am not manipulating the stack correctly. Any ideas? Is it even possible to recover?

Thanks,

Niel

Re: simple assembly "illegal instruction" exception handler

taigbr — Thu, 26 Mar 2009 17:27:22 GMT

Hi Niel,

since you try to return with a RTE the processor expects to find

a format field on the stack. You probably intended to return with

a RTS instruction. Take a look into the documentation about

"Exception Stack Frame Definition".

Regards, Georg

Re: simple assembly "illegal instruction" exception handler

order324 — Fri, 27 Mar 2009 04:00:41 GMT

Ok that seemed to fix it. I had read the section about the two entries on the stack but it was not clear to me that the rte read back that info and used it.

Thanks,

Niel