passport/src/id/daviddos.a

;-------------------------------
; IDDavid
; identify David-DOS bootloader
;
; in:    $0800..$08FF contains T00,S00
;        first page of track buffer also contains T00,S00
;        A = 0
;        X = 0
; out:   C clear if David-DOS bootloader found
;        C set otherwise
;        A = 0
;        X = 0
;        all other registers & flags clobbered
;-------------------------------
!macro IDDavid {
         ldy   #$07
         jsr   compare    ; if T00,S00,$00 ==
         !byte $01
         !byte $A5,$27    ; LDA $27
         !byte $C9,$09    ; CMP #$09
         !byte $D0,$17    ; BNE +$17
         bcs   @notDavid
         ldx   #$4A
         dey
         jsr   compare    ; and T00,S00,$4A ==
         !byte $A2,WILDCARD    ; LDX #$**
         !byte $BD,WILDCARD,$08; LDA $08**,X
         !byte $9D
                          ; passport-test-suite/Horses.woz [C=0] matches
         tax
@notDavid
}