Apple-2-SW/Apple-6502-Scaffold
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Refactoring and cleanup

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This commit is contained in:
Lee Fastenau 2019-04-12 00:50:47 -07:00
parent 14bf02cf3d
commit e74753c583
3 changed files with 65 additions and 20 deletions
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62
include/print
View File

@ -1,23 +1,51 @@
; ****************************************
; 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 $06
pla
sta $07
ldy #0
sta zp$+1
ldy #0 ; Y always 0 since we're incrementing the addr itself
.loop
inc $06
inc zp$ ; Increment zero page addr
bne .next
inc $07
inc zp$+1
.next
lda ($06),y
beq .done
ora #$80
jsr COUT
bne .loop
lda (zp$),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
inc $06
bne .end
inc $07
.end
jmp ($06)
jsr CROUT ; Print carriage return at end of string
lda zp$+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

7
include/stdio
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@ -1,6 +1,13 @@
; ****************************************
; stdio
; ****************************************
;
; Source:
; Assembly Cookbook for the Apple II/IIe part two by Don Lancaster
; https://www.americanradiohistory.com/Archive-Don-Lancaster/aacb2.pdf
;
; NOTE: This was copied from the above PDF and required some gentle
; massaging due to OCR errors. Not guaranteed to be typo-free.
WNDLFT EQU $20 ; SCROLL WINDOW LEFT
WNDWDTH EQU $21 ; SCROLL WINDOW WIDTH

16
src/main.asm
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@ -1,11 +1,21 @@
; ****************************************
; main.asm
; Copyright (C) 20XX [your_name_here]
; ****************************************
processor 6502
incdir "include"
seg main
; ****************************************
; main
; ****************************************
seg
org $c00
main subroutine
jsr HOME
jsr HOME ; Clear the screen
jsr print
byte "YOUR PROGRAM WORKED!",0
@ -13,7 +23,7 @@ main subroutine
jsr print
byte '","CALL ",[main]d,'"," TO RUN AGAIN.",0
jmp DOSWRM
jmp DOSWRM ; Return to Applesoft
; ****************************************
; includes