aboutsummaryrefslogtreecommitdiff
path: root/src/col80_modified/cruft/col80_main.s
blob: 0ced210c5e7dca2efcb0beff4c2c2b0ad754b2ea (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
; THIS IS A MODIFIED VERSION, for use with FujiChat

; COL80.COM, aka COL80E.COM, aka COL80HND.COM
; (and probably several other names)

; Original author unknown
; License unknown
; Disassembly and comments by Urchlay

; This is a widely-distributed software 80-column driver for the Atari
; 8-bit computers. It replaces the OS's E: driver, and uses GRAPHICS 8
; for display, with 4x8 pixel character cells.

; Disassembly was done with da65, with many iterations of "edit the
; .info file, disassemble again", and the results were tweaked by hand
; into something assemblable by dasm (and fairly compatible with other
; assemblers).


 .include "col80_include.s"

; START_ADDRESS is defined in col80_startaddr.s
 .org START_ADDRESS

; ----------------------------------------------------------------------------
; Start of COL80. The font is stored in packed form. Each group of 8 bytes
; defines two glyphs: the upper 4 bits of the 8 bytes, taken together,
; define the bitmap for the first glyph, and the lower 4 bits are the second.
; Note that the bits that make up a single character are spread across 8
; bytes, so it's hard to visualize these even if you're used to reading hex
; dumps.

; The first 2 characters look like:

; .... .O.. ; $04
; .... .O.. ; $04
; O.O. .O.. ; $A4
; OOO. .O.. ; $E4
; OOO. .OOO ; $E7
; .O.. .O.. ; $44
; .... .O.. ; $04
; .... .O.. ; $04

; These are the ATASCII heart symbol (character code 0) and the ATASCII
; control-A line-drawing symbol (code 1).

; Note: unlike the ROM font, this font is stored in ATASCII order instead
; of the standard Atari character order imposed by the hardware. Like
; the ROM font, inverse characters are not stored here (the bitmaps get
; inverted by the driver)

font_data:
 .ifdef FUJICHAT
  .include "new_font.s"
 .else
        ; Low ATASCII graphics symbols (code 0-31)
        .byte   $04,$04,$A4,$E4,$E7,$44,$04,$04
        .byte   $14,$14,$14,$14,$1C,$10,$10,$10
        .byte   $40,$40,$40,$40,$CC,$44,$44,$44
        .byte   $18,$18,$24,$24,$42,$42,$81,$81
        .byte   $10,$10,$30,$30,$73,$73,$F3,$F3
        .byte   $83,$83,$C3,$C3,$E0,$E0,$F0,$F0
        .byte   $CF,$CF,$C0,$C0,$00,$00,$00,$00
        .byte   $00,$00,$00,$00,$0C,$0C,$FC,$FC
        .byte   $00,$00,$00,$40,$A7,$44,$E4,$04
        .byte   $04,$04,$04,$04,$FF,$04,$04,$04
        .byte   $00,$00,$60,$F0,$FF,$6F,$0F,$0F
        .byte   $80,$80,$80,$80,$8F,$84,$84,$84
        .byte   $4C,$4C,$4C,$4C,$FC,$0C,$0C,$0C
        .byte   $40,$4C,$48,$4C,$78,$0C,$06,$00
        .byte   $00,$44,$E4,$44,$4E,$44,$00,$00
        .byte   $00,$24,$42,$FF,$42,$24,$00,$00

        ; Space ! " # etc (codes 32-63)
        .byte   $00,$04,$04,$04,$04,$00,$04,$00
        .byte   $00,$A0,$AA,$AE,$0A,$0E,$0A,$00
        .byte   $00,$40,$68,$82,$44,$28,$C2,$40
        .byte   $00,$C4,$64,$E4,$60,$C0,$40,$00
        .byte   $00,$44,$82,$82,$82,$82,$82,$44
        .byte   $00,$04,$A4,$4E,$E4,$44,$A0,$00
        .byte   $00,$00,$00,$0E,$00,$40,$40,$80
        .byte   $00,$02,$02,$04,$04,$08,$48,$00
        .byte   $00,$E4,$AC,$A4,$A4,$A4,$EE,$00
        .byte   $00,$EE,$22,$22,$EE,$82,$EE,$00
        .byte   $00,$AE,$A8,$AE,$E2,$22,$2E,$00
        .byte   $00,$EE,$82,$E2,$A4,$A4,$E4,$00
        .byte   $00,$EE,$AA,$EA,$AE,$A2,$EE,$00
        .byte   $00,$00,$00,$44,$00,$44,$04,$08
        .byte   $00,$20,$4E,$80,$4E,$20,$00,$00
        .byte   $00,$8C,$42,$22,$44,$80,$04,$00

        ; @ A B C etc (codes 64-95)
        .byte   $00,$6E,$9A,$BA,$BE,$8A,$6A,$00
        .byte   $00,$C6,$A8,$C8,$A8,$A8,$C6,$00
        .byte   $00,$CE,$A8,$AC,$A8,$A8,$CE,$00
        .byte   $00,$E6,$88,$C8,$8A,$8A,$86,$00
        .byte   $00,$AE,$A4,$E4,$A4,$A4,$AE,$00
        .byte   $00,$2A,$2A,$2C,$2A,$2A,$CA,$00
        .byte   $00,$8A,$8E,$8E,$8A,$8A,$EA,$00
        .byte   $00,$C4,$AA,$AA,$AA,$AA,$A4,$00
        .byte   $00,$EE,$AA,$EA,$8A,$8A,$8E,$03
        .byte   $00,$C6,$A8,$AC,$C2,$A2,$AC,$00
        .byte   $00,$EA,$4A,$4A,$4A,$4A,$4E,$00
        .byte   $00,$AA,$AA,$AA,$AE,$AE,$4A,$00
        .byte   $00,$AA,$4A,$4E,$44,$44,$A4,$00
        .byte   $00,$EE,$28,$48,$88,$88,$E8,$0E
        .byte   $00,$8E,$82,$42,$42,$22,$22,$0E
        .byte   $00,$00,$40,$A0,$00,$00,$00,$0F

        ; diamond, lowercase letters, control codes (codes 96-127)
        .byte   $00,$00,$00,$46,$E2,$4E,$0E,$00
        .byte   $00,$80,$80,$C6,$A8,$A8,$C6,$00
        .byte   $00,$20,$20,$6E,$AE,$A8,$6E,$00
        .byte   $00,$00,$C0,$86,$CA,$8E,$82,$0C
        .byte   $00,$80,$84,$80,$C4,$A4,$A4,$00
        .byte   $00,$08,$28,$0A,$2C,$2A,$2A,$C0
        .byte   $00,$40,$40,$4A,$4E,$4A,$4A,$00
        .byte   $00,$00,$00,$CE,$AA,$AA,$AE,$00
        .byte   $00,$00,$00,$C6,$AA,$C6,$82,$82
        .byte   $00,$00,$00,$6E,$88,$86,$8E,$00
        .byte   $00,$00,$40,$EA,$4A,$4A,$6E,$00
        .byte   $00,$00,$00,$AA,$AA,$AE,$4A,$00
        .byte   $00,$00,$00,$AA,$4A,$A6,$A2,$0C
        .byte   $00,$00,$04,$EE,$4E,$84,$EE,$00
        .byte   $40,$4E,$4C,$4E,$4A,$42,$42,$40
        .byte   $00,$28,$6C,$EE,$6C,$28,$00,$00
 .endif

right_margin:
        ; Default value is 79 decimal. Unsure why the author didn't use RMARGN at $53
        .byte   $4F

; ----------------------------------------------------------------------------
; Start of COL80 code.

; Callback for CIO OPEN command.

col80_open:
        jsr     init_graphics_8
        lda     #$00
        sta     ROWCRS
        sta     COLCRS
 .ifndef FUJICHAT
        nop
        nop
 .endif
        sta     BUFCNT
        lda     #$4F
        sta     right_margin
        rts

; ----------------------------------------------------------------------------
; Assembly version of GRAPHICS 8+16 command.

init_graphics_8:
        lda     #$08
        sta     ICAX2Z
        lda     #$0C
        sta     ICAX1Z
        jsr     open_s_dev

        ; Set COL80's default colors
        lda     #$08
        sta     COLOR2
 .ifndef FUJICHAT
        nop
        nop
        nop
 .endif
        lda     #$00
        sta     COLOR1

        ; Protect ourselves from BASIC and the OS
        lda     #<START_ADDRESS
        sta     MEMTOP
        lda     #>START_ADDRESS
        sta     MEMTOP+1
        rts

; ----------------------------------------------------------------------------
; Call the OPEN vector for the S: device, using the ROM vector table
; at $E410. The table stores address-minus-one of each routine, which is
; meant to actually be called via the RTS instruction (standard 6502
; technique, but confusing the first time you encounter it)

open_s_dev:
        lda     s_dev_open_hi
        pha
        lda     s_dev_open_lo
        pha
        rts

; ----------------------------------------------------------------------------
; Callback for CIO CLOSE command. Note that the routine does nothing, really
; (the OS will mark the E: device as being closed, but COL80 doesn't do any
; cleanup).
; The SPECIAL and GET STATUS callbacks in col80_vector_tab also point here.

col80_close:
        jmp return_success

; ----------------------------------------------------------------------------
; Callback for the internal put-one-byte, used by the OS to implement the
; CIO PUT RECORD and PUT BYTES commands. This routine's one argument is
; the byte in the accumulator (the character to print).

; First, the routine checks for the cursor control characters it supports.
; COL80 only handles the EOL and clear-screen codes; trying to print
; backspaces, arrows, deletes, inserts, etc just causes their ATASCII
; graphics character to print instead.

col80_putbyte:
        ; EOL (decimal 155)?
        cmp     #$9B
        bne     check_clear
        lda     right_margin
        sta     COLCRS
        jmp     skip_write

check_clear:
 .ifndef FUJICHAT ; save memory by not including clear_screen
                  ; (also, this lets us print the } character)
        ; Clear (decimal 125)?
        cmp     #$7D
        bne     regular_char
        jmp     clear_screen
 .endif

        ; See if this is an inverse video char (code >= 128)
regular_char:
        tax
        bpl     not_inverse
        lda     #$FF
        sta     inverse_mask
        bne     skip_ninv

not_inverse:
        lda     #$00
        sta     inverse_mask

skip_ninv:
        txa
        and     #$7F
 .ifdef FUJICHAT ; mask out low ASCII
        sec
        sbc #$20
        bcs not_low_ascii
        jmp return_success
not_low_ascii:
 .endif
        sta     TMPCHR
        lda     DINDEX
        cmp     #$08
        beq     graphics_ok
        ; If we're not in GRAPHICS 8 mode, reinitialize ourselves
        jsr     col80_open

graphics_ok:
        ; Call the routines that actually print the character
        jsr     setup_font_ptr
        jsr     setup_screen_ptr
        jsr     write_font_data

skip_write:
        ; Move the cursor 1 space to the right. This will
        ; advance us to the next line if we're at the margin,
        ; and scroll the screen if needed
        jsr     advance_cursor

check_ssflag:
        ; The OS keyboard interrupt handler will toggle SSFLAG (start/stop fla
        ; any time the user presses ctrl-1
        lda     SSFLAG
        bne     check_ssflag
        jmp     return_success

; ----------------------------------------------------------------------------
; Scroll the screen up one line (8 scanlines). This has to move almost 8K of
; data, so it's noticeably slower than scrolling the GR.0 text screen.

scroll_screen:
        lda     SAVMSC
        sta     screen_ptr_lo
        clc
        adc     #$40
        ; font_ptr_lo is actually being used here as a second pointer into
        ; screen RAM, instead of its usual use as a pointer into the
        ; font_data table
        sta     font_ptr_lo
        lda     SAVMSC+1
        sta     screen_ptr_hi
        adc     #$01
        sta     font_ptr_hi
        ldx     #$1D
        ldy     #$00

scroll_line_loop:
        lda     (font_ptr_lo),y
        sta     (screen_ptr_lo),y
        dey
        bne     scroll_line_loop
        inc     font_ptr_hi
        inc     screen_ptr_hi
        dex
        bne     scroll_line_loop

blank_bottom_row:
        lda     SAVMSC
        clc
        adc     #$C0
        sta     screen_ptr_lo
        lda     SAVMSC+1
        adc     #$1C
        sta     screen_ptr_hi
        lda     #$00
        tay

blank_loop:
        sta     (screen_ptr_lo),y
        dey
        bne     blank_loop
        inc     screen_ptr_hi
        ldy     #$40

blank_tail:
        sta     (screen_ptr_lo),y
        dey
        bpl     blank_tail
        rts

; ----------------------------------------------------------------------------
; Set up font_ptr_lo/hi to point to the font_data bitmap for the character in
; TMPCHR. Also sets lo_nybble_flag to let the caller know whether the
; bitmap is in the upper or lower 4 bits of the bytes pointed to.

setup_font_ptr:
        lda     #$00
        sta     font_ptr_hi
        sta     lo_nybble_flag
        lda     TMPCHR
        clc
        ror
        bcc     font_hi_nybble
        ldx     #$FF
        stx     lo_nybble_flag

font_hi_nybble:
        clc
        rol
        rol
        rol     font_ptr_hi
        rol
        rol     font_ptr_hi
        adc     #<font_data
        sta     font_ptr_lo
        lda     #>font_data
        adc     font_ptr_hi
        sta     font_ptr_hi
        rts

; ----------------------------------------------------------------------------
; Move the cursor one space to the right (to the next line if at the margin,
; and scroll screen if on the last row)

advance_cursor:
        inc     COLCRS
        lda     right_margin
        cmp     COLCRS
        bcs     same_line
        lda     LMARGN
        sta     COLCRS
        lda     ROWCRS
        ; $17 is 25 decimal, one row below the lowest on the screen
        cmp     #$17
        bcc     no_scroll
        jsr     scroll_screen
        ; Move to row 24 after scrolling
        lda     #$16
        sta     ROWCRS

no_scroll:
        inc     ROWCRS

same_line:
        rts

; ----------------------------------------------------------------------------
; Clear the screen by setting all screen RAM bytes to zero. Slow, but not
; as slow as scrolling.

 .ifndef FUJICHAT
clear_screen:
        lda     SAVMSC
        sta     screen_ptr_lo
        lda     SAVMSC+1
        sta     screen_ptr_hi
        ldy     #$00
        ldx     #$1D
        lda     #$00

cls_loop:
        sta     (screen_ptr_lo),y
        dey
        bne     cls_loop
        inc     screen_ptr_hi
        dex
        bne     cls_loop
        jsr     blank_bottom_row
        lda     LMARGN
        sta     COLCRS
        lda     #$00
        sta     ROWCRS
        ; redundant JMP
        jmp     return_success
 .endif

; ----------------------------------------------------------------------------
; CIO expects the Y register to contain a status code.
; 1 means success (no error). Lots of COL80's routines
; jump here.

return_success:
        ldy     #$01
        rts

; ----------------------------------------------------------------------------
; Set screen_ptr_lo/hi to point to the address of the first byte of graphics
; data at the current cursor position.

setup_screen_ptr:
        ldy     ROWCRS
        lda     SAVMSC
        clc
        adc     row_low_offset_tab,y
        sta     screen_ptr_lo
        lda     SAVMSC+1
        adc     row_high_offset_tab,y
        sta     screen_ptr_hi
        lda     COLCRS
        lsr
        clc
        adc     screen_ptr_lo
        bcc     hi_byte_ok
        inc     screen_ptr_hi

hi_byte_ok:
        sta     screen_ptr_lo
        rts

; ----------------------------------------------------------------------------
; Tables of offsets for setup_screen_ptr, to avoid doing multiplication at
; runtime (the 6502 lacks a MUL instruction, so it's slow...)

row_low_offset_tab:
        .byte   $00,$40,$80,$C0,$00,$40,$80,$C0
        .byte   $00,$40,$80,$C0,$00,$40,$80,$C0
        .byte   $00,$40,$80,$C0,$00,$40,$80,$C0

row_high_offset_tab:
        .byte   $00,$01,$02,$03,$05,$06,$07,$08
        .byte   $0A,$0B,$0C,$0D,$0F,$10,$11,$12
        .byte   $14,$15,$16,$17,$19,$1A,$1B,$1C

; ----------------------------------------------------------------------------
; Copy pixel data from the font table to screen RAM.
; font_ptr_lo/hi must point to the correct character, and screen_ptr_lo/hi
; must point to the correct screen address for the current cursor position.
; This routine has separate execution paths for even- and odd-numbered
; cursor positions, since each byte of screen RAM holds data for two
; adjacent characters (and when printing to one of them, the other needs
; to be left undisturbed!)

write_font_data:
        lda     COLCRS
        clc
        ror
        bcc     write_font_data_even
        ldx     #$00
        ldy     #$00

get_font_nybble_odd:
        lda     (font_ptr_lo),y
        bit     lo_nybble_flag
        bne     lo_nybble_odd
        ; glyph we want is stored in top 4 bits of font byte,
        ; shift it down to the bottom 4 bits
        lsr
        lsr
        lsr
        lsr

lo_nybble_odd:
        eor     inverse_mask
        and     #$0F
        sta     TMPCHR
        ldy     scanline_offset_tab,x
        lda     (screen_ptr_lo),y
        and     #$F0
        ora     TMPCHR
        sta     (screen_ptr_lo),y
        inx
        cpx     #$07
        bne     screen_ptr_ok_odd
        inc     screen_ptr_hi

screen_ptr_ok_odd:
        cpx     #$08
        beq     write_font_done_odd
        txa
        tay
        bne     get_font_nybble_odd

write_font_done_odd:
        rts

; ----------------------------------------------------------------------------
; Write data to even-numbered columns, very similar to the above

write_font_data_even:
        ldx     #$00
        ldy     #$00

get_font_nybble_even:
        lda     (font_ptr_lo),y
        bit     lo_nybble_flag
        beq     hi_nybble_even
        asl
        asl
        asl
        asl

hi_nybble_even:
        eor     inverse_mask
        and     #$F0
        sta     TMPCHR
        ldy     scanline_offset_tab,x
        lda     (screen_ptr_lo),y
        and     #$0F
        ora     TMPCHR
        sta     (screen_ptr_lo),y
        inx
        cpx     #$07
        bne     screen_ptr_ok_even
        inc     screen_ptr_hi

screen_ptr_ok_even:
        cpx     #$08
        beq     write_font_done_even
        txa
        tay
        bne     get_font_nybble_even

write_font_done_even:
        rts

; ----------------------------------------------------------------------------

scanline_offset_tab:
        .byte   $00,$28,$50,$78,$A0,$C8,$F0,$18

; ----------------------------------------------------------------------------
; Callback for the internal get-one-byte, used by the OS to implement the
; CIO GET RECORD and GET BYTES commands. This routine takes no arguments,
; and returns the read byte in the accumulator.

; Internally, COL80 maintains a line buffer. Each time col80_getbyte is
; called, it returns the next character in the buffer. If the buffer's
; empty (or if the last call returned the last character), a new line
; of input is read from the user (and the first character is returned).
; This is exactly how the OS E: device works.

col80_getbyte:
        lda     BUFCNT
        beq     get_line

get_next_byte:
        ldx     line_buffer_index
        lda     line_buffer,x
        dec     BUFCNT
        inc     line_buffer_index
        jmp     return_success

; ----------------------------------------------------------------------------
; Get a line of input from the user, terminated by the Return key.

get_line:
        lda     #$00
        sta     BUFCNT
        sta     line_buffer_index

show_cursor:
 .ifdef FUJICHAT
        lda     #$00
 .else
        lda     #$20
 .endif
        sta     TMPCHR
        lda     #$FF
        sta     inverse_mask
        jsr     setup_font_ptr
        jsr     setup_screen_ptr
        jsr     write_font_data
        jsr     get_keystroke
        cpy     #$01
        beq     keystroke_ok
 .ifdef FUJICHAT
        dey ; yes, we really care about 1-byte optimizations
 .else
        ldy     #$00
 .endif
        sty     line_buffer_index
        sty     BUFCNT

keystroke_ok:
 .ifdef FUJICHAT
        cmp #$20
		  bcc show_cursor ; ignore low ASCII
 .endif
        cmp     #$9B
        bne     check_backs_key
        jmp     return_key_hit

check_backs_key:
        cmp     #$7E
        bne     check_clear_key
        jmp     backs_key_hit

check_clear_key:
        cmp     #$7D
        bne     normal_key_hit
        jmp     clear_key_hit

normal_key_hit:
        ldx     BUFCNT
        bpl     buffer_character
 .ifdef FUJICHAT
        jmp show_cursor
 .else
        jmp     beep
 .endif

buffer_character:
        sta     line_buffer,x
        jsr     col80_putbyte
        inc     BUFCNT
        jmp     show_cursor

return_key_hit:
        jsr     print_space
        lda     #$9B
        ldx     BUFCNT
        sta     line_buffer,x
        inc     BUFCNT
        jsr     col80_putbyte
        jmp     get_next_byte

clear_key_hit:
 .ifndef FUJICHAT
        jsr     clear_screen
 .endif
        lda     #$00
        sta     line_buffer_index
        sta     BUFCNT
        jmp     get_line

backs_key_hit:
        jsr     print_space
        lda     BUFCNT
        beq     backs_key_done
        dec     COLCRS
        lda     COLCRS
        clc
        adc     #$01
        cmp     LMARGN
        bne     backs_same_line
        lda     right_margin
        sta     COLCRS
        dec     ROWCRS

backs_same_line:
        dec     BUFCNT

backs_key_done:
        jmp     show_cursor

; ----------------------------------------------------------------------------
; Ring the margin bell. COL80 doesn't implement the ctrl-2 bell (character
; 253), and instead of using the GTIA keyclick speaker, it uses POKEY to
; make a beep

 .ifndef FUJICHAT
beep:   ldy     #$00
        ldx     #$AF

beep_delay_x:
        stx     AUDF1
        stx     AUDC1

beep_delay_y:
        dey
        bne     beep_delay_y
        dex
        cpx     #$9F
        bne     beep_delay_x
        jmp     show_cursor
 .endif

; ----------------------------------------------------------------------------
; Print a space character at the current cursor position. Does not
; update the cursor position.
print_space:
        lda     #$00
        sta     inverse_mask
 .ifndef FUJICHAT
        lda     #$20
 .endif
        sta     TMPCHR
        jsr     setup_font_ptr
        jsr     setup_screen_ptr
        jsr     write_font_data
        rts

; ----------------------------------------------------------------------------
; Get a keystroke (blocking). Just calls the OS K: get-one-byte routine
; (call by pushing address-minus-one then doing an RTS)
get_keystroke:
        lda     k_dev_get_hi
        pha
        lda     k_dev_get_lo
        pha
        rts

 .ifndef FUJICHAT
 .include "col80_init.s"
 .endif

; ----------------------------------------------------------------------------
; COL80 vector table, in the format required by the OS. Our HATABS entry
; will point to this table, and the OS will call the routines listed here
; via the "call by RTS" method (which is why they're address-minus-one).

; See the entry on HATABS in "Mapping the Atari" or the OS manual.

col80_vector_tab:
        .word   col80_open-1
        .word   col80_close-1
        .word   col80_getbyte-1
        .word   col80_putbyte-1
        .word   col80_close-1
        .word   col80_close-1
 .ifdef FUJICHAT
        .byte 0, 0, 0 ; heh.
 .else
        jmp     col80_init
 .endif

 .ifndef FUJICHAT
 .include "col80_entry.s"
 .endif

; ----------------------------------------------------------------------------
; Various bits of runtime state here. It's unclear to me why the standard
; OS buffer location couldn't have been used instead (normally the top
; half of page 5), or why the other stuff couldn't have been stored in
; zero page, in locations used by the ROM E: handler (thus unused when
; it's replaced with COL80). line_buffer_index needs to be preserved
; across calls to col80_getbyte, but lo_nybble_flag and inverse_mask are
; freshly calculated every time they're used, so they could be almost
; anywhere.

 .ifdef FUJICHAT
 .segment "CODE"
 .endif

lo_nybble_flag:
        .byte   $00

inverse_mask:
        .byte   $00

line_buffer_index:
        .byte   $12

; ----------------------------------------------------------------------------
; There's absolutely no reason why this data needs to be included in the
; binary load file: the line buffer's initial contents are meaningless, they
; will be blown away the first time anything reads from the E: device.

; Notice the author was running his debugger in COL80 when he built the
; binary (ASCII "S COL80 7A00 7F80" command still in the buffer).

 .ifdef FUJICHAT
line_buffer = $03FD ; cassette buffer
 .else
line_buffer:
        .byte   $53,$20,$43,$4F,$4C,$38,$30,$20
        .byte   $37,$41,$30,$30,$20,$37,$46,$38
        .byte   $30,$9B,$20,$20,$20,$20,$9B,$27
        .byte   $40,$40,$40,$40,$28,$28,$28,$28
        .byte   $40,$40,$40,$40,$40,$40,$40,$40
        .byte   $40,$40,$40,$40,$40,$40,$40,$40
        .byte   $9B,$FD,$FD,$FD,$FD,$9B
 .endif

END_ADDRESS = *-1

; I've found a variant (modified version?) of this code, that doesn't
; include the line_buffer in the file (no reason for it to be there),
; or the $0C segment, and that has another segment, loaded at $6000,
; with the run address changed to $6000.  The code looks like:

; .org $6000
; jsr dosini_entry_point
; lda #$50
; sta RMARGN
; lda #$00
; sta COLOR2

; also, the default colors have been changed in init_graphics_8.

; There are at least two binaries floating around that contain
; extra (garbage) bytes at the end, presumably from being transferred
; over XMODEM or similar. They are otherwise identical.