panic.a

        ; panic.a - fatal error handler for 6809

        include "globals.i"
        include "via6522.i"

        ORG     $0000           ; This is a relocatable module.
        EXEC    init

        ; Default panic handler, outputs to [g_stderr].
panic:  begin                   ; 6809 SWI entry point.
            nop                 ; Needed because of error in pcr assembly, above.
            ldx     10,s        ; Get saved PC from stack (points at panic string).
            ; Count the length of the panic string.
            ldd     #0          ; Clear D (length counter).
count:      lda     ,x+         ; Get next byte of string.
            beq     done        ; Is this the end of the string?
            addd    #1          ; Increment length counter.
            bra     count
            ; Output the panic string to stderr.
done:       ldx     10,s        ; Get panic string (== saved PC) from stack again.
            jsr     [g_stderr]  ; Output the panic string.

loopstop:   bra loopstop        ; Loop here forever, with interrupts disabled.
        end

        ; Initialisation routine to set up the panic handler and stderr.
init:   begin
            leax    panic,pcr   ; Copy the address of the panic handler
            stx     g_swivec    ; to the SWI vector.
            rts                 ; Done, return to the loader.
        end