From 9852fbd5641ac12949c8db9721fec2db5f1f8d98 Mon Sep 17 00:00:00 2001
From: Christopher RYU <software-ryucats@disavowed.jp>
Date: Tue, 3 Oct 2023 18:46:43 +0900
Subject: [PATCH] Checkpoint comments.

---
 bitsy.bye.s | 140 ++++++++++++++++++++++++++++++----------------------
 1 file changed, 80 insertions(+), 60 deletions(-)

diff --git a/bitsy.bye.s b/bitsy.bye.s
index ff1537b..a28aa2b 100644
--- a/bitsy.bye.s
+++ b/bitsy.bye.s
@@ -3,9 +3,16 @@
 ; Input file: bitsy.bye
 ; Page:       1
 
+OPEN_BUFFER     := $0280
 L2000           := $2000
+L1400           := $1400
 
 PRODOS_MLI      := $BF00
+DEVNUM          := $BF30
+BITMAP          := $BF58
+
+DRVSM2          := $C082
+
 INIT            := $FB2F
 BASCALC         := $FBC1
 BELL1           := $FBDD
@@ -24,7 +31,7 @@ NEWVIDEO        := $C029
 .org    $1000
 
         cld
-        lda     $C082
+        lda     DRVSM2          ; turn all drive phases off
         cli
         sta     CLR80VID
         sta     CLR80COL
@@ -35,26 +42,27 @@ NEWVIDEO        := $C029
         jsr     HOME
         ldx     #$DF
         lda     #$CF
-L101E:  sta     $BE79,x
-        lda     L1270,x
-        sta     $7A,x
+L101E:  sta     BITMAP-$df,x    ; $BF58, aka BITMAP
+        lda     L135F -$df,x    ; $134F
+        sta     $7A,x           ; $0159
         lda     #$00
         txs
         inx
         bne     L101E
-        .byte   $C2
-        .byte   $02
-        beq     L1034   ; f0 04
-        inx             ; e8
-        stx     NEWVIDEO
-L1034:  inc     $BF6F
-        ldx     #$57
-L1039:  lda     L12FF,x
+.setcpu "65816"                 ; this is a NOP on 65x02
+        rep     #$02            ; reset processor status bits
+.setcpu "6502"
+        beq     L1034           ; branch-always on 6502
+        inx                     ; only //gs
+        stx     NEWVIDEO        ; only //gs
+L1034:  inc     BITMAP+$17      ; bitmap of low 48k of memory
+        ldx     #(L1356-L12FE-1)  ; $57
+L1039:  lda     L12FE+1,x         ; $1356
         bmi     L1045
-        jsr     BASCALC
+        jsr     BASCALC         ; row in a -> screen address in ($28)
         ldy     L1300,x
         .byte   $2C             ; mask next ...
-L1045:  sta     ($28),y
+L1045:  sta     ($28),y         ; store directly to $(SCREEN) from BASCALC
         dey
         dex
         bne     L1039
@@ -62,24 +70,27 @@ L104B:  sta     $0480,y
         sta     ($28),y
         dey
         bpl     L104B
-        lda     $BF30
-        lsr     a
-        lsr     a
-        lsr     a
+
+; done drawing screen
+
+        lda     DEVNUM          ; get current active slot (DSSS/0000)
+        lsr     a               ; for 7, that's 0111/0000
+        lsr     a               
+        lsr     a               ; now 0000/1110
         tax
         inx
-        cmp     #$10
+        cmp     #$10            ; legit slot?
         bcc     L1060
 L105F:  dex
-L1060:  jsr     L1254
+L1060:  jsr     OPEN_PREFIX
         beq     L105F
-L1065:  lda     #$14
-        sta     $7B
-        sta     $59
-        ldy     #$00
+L1065:  lda     #>L1400
+        sta     $7A+1
+        sta     $58+1
+        ldy     #<L1400
         sty     $7A
         sty     $58
-        jsr     L1294
+        jsr     OPEN_FILE
         cpy     #$4C
         beq     L107B
         jsr     BELL1
@@ -173,9 +184,11 @@ L1120:  inx
         cpx     #$14
         bcc     L10AC
         stx     $29
-        jsr     RDKEY
-        cmp     #$8D
+        jsr     RDKEY           ; get keypress
+        cmp     #$8D            ; CR?
         bne     L11A8
+
+; try to load and execute the selected file
         jsr     PRODOS_MLI      ; SET_PREFIX
         .byte   $c6
         .word   L12FD
@@ -192,14 +205,14 @@ L113F:  stx     $7B
         sta     ($5C),y
         inc     $74
         dey
-        jsr     L1294
+        jsr     OPEN_FILE
         dey
         bmi     L1164
         ldx     L10B9+1
         lda     #$C3
         sta     $0305,x
         ldy     #$FF
-L115C:  jsr     L1294
+L115C:  jsr     OPEN_FILE
         dec     $74
         dey
         bpl     L11A2
@@ -208,7 +221,7 @@ L1166:  lda     ($5C),y
         sta     $2006,y
         dey
         bpl     L1166
-L116E:  jsr     HOME
+EXEC_FILE:  jsr     HOME
         jmp     L2000
 
 L1174:  tay
@@ -216,7 +229,7 @@ L1174:  tay
         sta     $57
         tax
 L117A:  lda     ($5C),y
-        sta     $0280,x
+        sta     OPEN_BUFFER,x
         dex
         dey
         bpl     L117A
@@ -224,11 +237,12 @@ L117A:  lda     ($5C),y
         lda     #$AF
         sta     $0281,x
         bcs     L11A5
-        jsr     L1294
+        jsr     OPEN_FILE
         tya
-        beq     L116E
+        beq     EXEC_FILE
 L1191:  jsr     BELL1
-L1194:  ldy     $57
+
+BROWSER_BACK:  ldy     $57
 L1196:  lda     ($73),y
         dey
         beq     L11A2
@@ -240,7 +254,7 @@ L11A2:  jsr     BELL1
 L11A5:  jmp     L1065
 
 L11A8:  ldx     $5E
-        cmp     #$95
+        cmp     #$95            ; right-arrow?
         bne     L11E5
 L11AE:  inx
         ldy     #$10
@@ -271,16 +285,16 @@ L11D4:  eor     #$F8
         bne     L11E0
         bcs     L11E0
         dex
-L11E0:  jsr     L1254
+L11E0:  jsr     OPEN_PREFIX
         bpl     L11A5
-L11E5:  cmp     #$9B
-        beq     L1194
-        cmp     #$C1
-        bcs     L1221
-        adc     #$48
+L11E5:  cmp     #$9B            ; ESC?
+        beq     BROWSER_BACK
+        cmp     #$C1            ; A?
+        bcs     L1221           ; branch if less than or equal to ...
+        adc     #$48            ; carry clear, so assume this is minimum $FA
         cmp     #$F9
-        bcs     L11D4
-        sbc     #$CF
+        bcs     L11D4           ; if we are <= $F9, go to L11D4
+        sbc     #$CF            ; now minimum $2c - "+"
         beq     L1201
         tay
         dey
@@ -337,7 +351,8 @@ L124A:  dex
         lda     #$14
         sta     $5D
         bne     L1235
-L1254:  txa
+
+OPEN_PREFIX:  txa
         and     #$0F
         sta     $56
         lsr     a
@@ -374,18 +389,18 @@ L127C:  ldy     #$AF
         dey
         rts
 
-L1294:  lda     $57
-        sta     $0280
+OPEN_FILE:  lda     $57
+        sta     OPEN_BUFFER
         jsr     PRODOS_MLI      ; open
         .byte   $c8
         .word   $0072
-        bcs     L12F3
+        bcs     BB_EXIT
         lda     $77
         sta     $79
         sty     $7D
         lda     #$2B
         ldx     #$0D
-        .byte   $2C     ; mask next
+        .byte   $2C             ; mask next
 L12AC:  lda     #$27
         dex
         bne     L12B5
@@ -396,9 +411,9 @@ L12B5:  sta     $7C
         .byte   $ca
         .word   $0078
         iny
-        beq     L12F3
+        beq     BB_EXIT
         lsr     $7E
-        beq     L12F3
+        beq     BB_EXIT
         tay
         lda     ($7A),y
         and     #$8F
@@ -426,15 +441,18 @@ L12DC:  tya
         bcc     L12AC
         inc     $7B
         bne     L12AC
-L12F3:  tay
-        jsr     PRODOS_MLI
+BB_EXIT:  tay
+        jsr     PRODOS_MLI      ; close all open files
         .byte   $cc
-        .word   L12FB
+        .word   CLOSE_ALL
         rts
 
-L12FB:  .byte   $01, $00
-L12FD:  .word   $8001
-L12FF:  .byte   $02
+; ProDOS MLI call parameters here
+
+CLOSE_ALL:  .byte   1, 0    ; one parameter, no reference, so close all
+L12FD:  .byte   1
+L12FE:  .word   OPEN_BUFFER
+
 L1300:  .byte   $ad, $16, $29
         scrcode "BITSY  BYE"
         .byte   $05, $24
@@ -447,12 +465,14 @@ L1300:  .byte   $ad, $16, $29
         scrcode "RETURN:SELECT"
         .byte   $17, $0d
         scrcode "ESC:BACK"
-        .byte   $17, $18
+        .byte   $17
+L134F:  .byte   $18        ; $18 is L134F
         scrcode "TAB,#:NEW VOL"
         .byte   $17, $28
-        scrcode "S6,D1:"
-        .byte   $00, $06
-        scrcode "/BASIS.SYSTEM"
+L135F:  scrcode "S6,D1:"
+        .byte   $00
+L1356:  .byte   $06
+L135q:  scrcode "/BASIS.SYSTEM"
 
         .byte   $02, $00, $81, $02, $03, $80, $02, $00, $0b, $00
 L136E:  .byte   $04, $FA, $06, $fc, $04