From e74753c583d4e3fe095079c48bd66668233e3b10 Mon Sep 17 00:00:00 2001
From: Lee Fastenau <lfastenau@opentable.com>
Date: Fri, 12 Apr 2019 00:50:47 -0700
Subject: [PATCH] Refactoring and cleanup

---
 include/print | 62 +++++++++++++++++++++++++++++++++++++--------------
 include/stdio |  7 ++++++
 src/main.asm  | 16 ++++++++++---
 3 files changed, 65 insertions(+), 20 deletions(-)

diff --git a/include/print b/include/print
index 52a9e7a..e1bc8da 100644
--- a/include/print
+++ b/include/print
@@ -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 ($06)
\ No newline at end of file
+                        jsr CROUT       ; Print carriage return at end of string
+
+                        lda zp$+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
diff --git a/include/stdio b/include/stdio
index b22dcf8..504af37 100644
--- a/include/stdio
+++ b/include/stdio
@@ -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
diff --git a/src/main.asm b/src/main.asm
index c95e016..daa5bca 100644
--- a/src/main.asm
+++ b/src/main.asm
@@ -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