185 lines
4.7 KiB
NASM
185 lines
4.7 KiB
NASM
; -----------------------------------------------------------
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; main.asm - Plus/4 demo: the Teletype Games title card
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; a colour wash runs across the title, the prompt blinks,
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; any key returns to BASIC
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; all timed by polling the TED raster beam
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;
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; Build: acme -f cbm -o plus4-demo.prg main.asm
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; Run: xplus4 plus4-demo.prg
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; -----------------------------------------------------------
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!cpu 6502
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!to "plus4-demo.prg", cbm
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; ---- TED registers ----
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TED_BG = $ff15 ; background colour
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TED_BORD = $ff19 ; border colour
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TED_RASTL = $ff1d ; raster line, low 8 bits
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TED_KBD = $ff08 ; keyboard row latch (write: latch, read: rows)
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KBD_COLS = $fd30 ; keyboard column select (0 = selected)
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SCREEN = $0c00 ; screen RAM (40x25 chars)
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COLRAM = $0800 ; colour RAM: luminance << 4 | hue
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CHROUT = $ffd2 ; KERNAL: print a character
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; ---- colours (luminance in the high nibble) ----
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BLACK = $00
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DARK_BLUE = $16
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CYAN = $53
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WHITE = $71
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GOLD = $47
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SYNC_LINE = $cc ; raster line the frame loop waits for
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; ---- layout ----
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TITLE_ROW = 8
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TITLE_COL = 13
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PROMPT_ROW = 20
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PROMPT_COL = 13
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; print a fixed text with one colour
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!macro prtext .row, .col, .color, .src, .len {
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ldx #0
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- lda .src, x
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sta SCREEN + .row * 40 + .col, x
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lda #.color
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sta COLRAM + .row * 40 + .col, x
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inx
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cpx #.len
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bne -
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}
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* = $1001
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; ---- BASIC stub: 10 SYS 4109 ----
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; so after LOAD"*",8,1 it's enough to type RUN
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!byte $0b, $10 ; address of next line
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!byte $0a, $00 ; line number: 10
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!byte $9e ; SYS token
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!text "4109" ; = $100d
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!byte $00 ; end of line
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!byte $00, $00 ; end of program
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start: ; = $100d
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lda #$93 ; clear the screen through the KERNAL: this also
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jsr CHROUT ; parks the cursor before the IRQ is stopped
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sei ; no KERNAL IRQ - raster polling must not jitter
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lda TED_BG
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sta saved_bg
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lda TED_BORD
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sta saved_bord
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lda #DARK_BLUE
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sta TED_BG
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lda #BLACK
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sta TED_BORD
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+prtext TITLE_ROW, TITLE_COL, WHITE, txt_title, TITLE_LEN
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+prtext 10, 14, CYAN, txt_sub, SUB_LEN
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+prtext 14, 8, GOLD, txt_line1, LINE1_LEN
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+prtext 15, 6, GOLD, txt_line2, LINE2_LEN
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+prtext PROMPT_ROW, PROMPT_COL, WHITE, txt_prompt, PROMPT_LEN
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lda #0
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sta framectr
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- jsr check_key ; the RETURN that started us may still be down
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bne -
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; ============================================================
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; main loop - one pass per frame
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; ============================================================
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main:
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jsr wait_frame
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inc framectr
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; colour wash: the ramp slides one cell every second frame
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lda framectr
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lsr
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sta wash_base
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ldx #0
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- txa
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clc
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adc wash_base
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and #$0f
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tay
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lda ramp, y
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sta COLRAM + TITLE_ROW * 40 + TITLE_COL, x
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inx
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cpx #TITLE_LEN
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bne -
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; blinking prompt: hidden while bit 5 of the frame counter is set
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lda framectr
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and #$20
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beq +
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lda #DARK_BLUE
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bne ++
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+ lda #WHITE
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++ ldx #0
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- sta COLRAM + PROMPT_ROW * 40 + PROMPT_COL, x
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inx
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cpx #PROMPT_LEN
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bne -
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jsr check_key
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beq main
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; ---- back to BASIC ----
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lda saved_bg
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sta TED_BG
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lda saved_bord
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sta TED_BORD
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cli
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lda #$93
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jsr CHROUT
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rts
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; ============================================================
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; wait_frame - wait for the raster beam to pass SYNC_LINE once
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; ============================================================
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wait_frame:
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- lda TED_RASTL
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cmp #SYNC_LINE
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bne -
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- lda TED_RASTL
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cmp #SYNC_LINE
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beq -
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rts
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; ============================================================
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; check_key - Z set when no key is pressed
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; all columns selected, joysticks deselected, rows latched
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; ============================================================
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check_key:
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lda #$00
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sta KBD_COLS
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lda #$ff
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sta TED_KBD
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lda TED_KBD
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cmp #$ff
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rts
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; ============================================================
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; data
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; ============================================================
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ramp: ; gold rising to white and back, 16 steps
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!byte $17, $27, $37, $47, $57, $67, $77, $71
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!byte $71, $77, $67, $57, $47, $37, $27, $17
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txt_title: !scr "teletype games"
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TITLE_LEN = * - txt_title
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txt_sub: !scr "plus/4 demo"
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SUB_LEN = * - txt_sub
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txt_line1: !scr "6502 assembly with acme"
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LINE1_LEN = * - txt_line1
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txt_line2: !scr "released through warpengine"
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LINE2_LEN = * - txt_line2
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txt_prompt: !scr "press any key"
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PROMPT_LEN = * - txt_prompt
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framectr: !byte 0
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wash_base: !byte 0
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saved_bg: !byte 0
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saved_bord: !byte 0
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