Apple-6502-Scaffold/include/print

; ****************************************
; print
; ****************************************
;
; A zero-terminated string should immediately follow "jsr print"
;
; Example:
; jsr print
; byte "HELLO WORLD",0
; [program resumes here]
;
; Destroys A, X, Y

print                   subroutine

zp$                     equ $06         ; Use some of that sweet, sweet zero page memory (non-destructive)

                        ldx zp$         ; Save zero page values to X and temp$
                        lda zp$+1
                        sta temp$

                        pla             ; Copy jsr return address from stack to zero page
                        sta zp$
                        pla
                        sta zp$+1

                        ldy #0          ; Y always 0 since we're incrementing the addr itself
.loop
                        inc zp$         ; Increment zero page addr
                        bne .next
                        inc zp$+1
.next
                        lda (zp$),y     ; Read the next character
                        beq .done       ; Done if 0 (string terminator)
                        ora #$80        ; Else make printable
                        jsr COUT        ; Output the character to the screen
                        bne .loop       ; Repeat
.done
                        jsr CROUT       ; Print carriage return at end of string

                        lda zp$+1       ; Copy zero page addr to stack for rts
                        pha
                        lda zp$
                        pha

                        stx zp$         ; Restore zero page values from X and temp$
                        lda #00         ; temp$ points to the immediate value here (self-modifying)
temp$                   equ .-1
                        sta zp$+1

                        rts             ; All done printing... that was kind of a pain