Errors

These are the error codes that QDOSMSQ can return from a vectored utility, a Trap or from SuperBasic extensions.

When writing assembler routines, it is always advised to explicitly check the value in D0.L for an error code. This is done quickest using :

        :
        trap    #n                ; Do the trap.
        tst.l   d0                ; Did it work?
        beq.s   all_ok            ; Yes, all is well

errors  :                         ; Handle errors here
        bra     kill_job          ; And exit the job, or code somehow.
        
all_ok  :                         ; Carry on from here if all worked.

Some traps and vectored utilities do not set the Z flag before returning which is why you have to do it. Well, actually, it's not that they don't set it but when you call a trap, the status register is stacked for the duration and restored at the end, so while D0 may have an appropriate error code in it, the Z flag's state is unknown. A vector should always have correctly set the Z flag, so save some coding and execution time by simply checking the Z flag, as follows:

        move.w  <whatever>,a2     ; Get the vectored routine.
        jsr     (a2)              ; Do it.
        beq.s   vec_ok            ; All is well, skip error handler.

v_error :                         ; Handle errors here
        bra     kill_job          ; And exit the job, or code somehow.
        
vec_ok  :                         ; Carry on from here if all worked.