frogman/setup.asm at main · mattgodbolt/frogman · GitHub

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; ============================================================================
; FROGMAN — Setup Code (Title Screen + Game Launcher)
;
; Displays the RLE-compressed title screen from Data2, waits for
; SPACE, then loads the game files and starts.
;
; Called from BASIC after level number is set at &0430.
;
; RLE format (source at &1300, dest starts at &3000):
;   bit7=0, bit6=0: literal — copy byte to dest, advance both
;   bit7=0, bit6=1: fill page — fill 256 bytes with (token & &3F)
;   bit7=1:         repeat — fill (next byte) copies of (token & &3F),
;                            advance dest by (next byte)
;   Decompression ends when dest high byte goes negative (>= &80)
; ============================================================================


.*setup_entry
{
    ; --- Blank display before mode change ---
        LDA #&01 : STA CRTC_ADDR  ; CRTC R1
        LDA #&00 : STA CRTC_DATA  ; Horizontal displayed = 0 (blank)

    ; --- MODE 2, cursor off ---
        LDA #&16 : JSR OSWRCH   ; VDU 22
        LDA #&02 : JSR OSWRCH   ; Mode 2

        LDA #&0A : STA CRTC_ADDR  ; CRTC R10
        LDA #&20 : STA CRTC_DATA  ; Cursor off

        LDA #&02 : STA OS_MODE

    ; --- Load title screen RLE data ---
        LDX #LO(oscli_load_data2)
        LDY #HI(oscli_load_data2)
        JSR OSCLI               ; *L.Data2 (&1300)

    ; --- RLE decompress: &1300 → &3000 (screen memory) ---
        LDA #&00 : STA &70      ; Source low
        LDA #&13 : STA &71      ; Source high (&1300)
        LDA #&00 : STA &72      ; Dest low
        LDA #&30 : STA &73      ; Dest high (&3000)

{
.token_loop
            LDY #&00
            LDA (&70),Y         ; Read token byte
            BMI repeat          ; Bit 7 set → repeat fill
            AND #&40
            BNE fill_page       ; Bit 6 set → page fill

    ; --- Literal: copy 1 byte ---
            LDA (&70),Y
            STA (&72),Y
            INC &70 : BNE skip1 : INC &71
.skip1
            INC &72 : BNE token_loop
            INC &73 : BPL token_loop
            JMP done

    ; --- Repeat: fill (count) bytes with (value) ---
.repeat
            AND #&3F            ; Value = token & &3F
            STA &74
            INY
            LDA (&70),Y         ; Count byte
            STA &75
            TAX                 ; X = count
            CLC
            LDA &70 : ADC #&02 : STA &70  ; Source += 2
            LDA &71 : ADC #&00 : STA &71
            LDY #&00
            LDA &74             ; Fill value
.repeat_loop
            STA (&72),Y
            INY
            DEX
            BNE repeat_loop
            CLC
            LDA &75 : ADC &72 : STA &72  ; Dest += count
            LDA &73 : ADC #&00 : STA &73
            BPL token_loop
            JMP done

    ; --- Fill page: fill 256 bytes with (value) ---
.fill_page
            LDA (&70),Y         ; Re-read token
            INC &70 : BNE skip2 : INC &71
.skip2
            AND #&3F            ; Fill value
            LDY #&00
.fill_loop
            STA (&72),Y
            INY
            BNE fill_loop
            INC &73
            BPL token_loop

.done
}

    ; --- Restore VIA for keyboard ---
        LDA #&7F : STA VIA_DDRA
        LDA #&FF : STA VIA_DDRB
        LDA #&03 : STA VIA_ORB

    ; --- Wait for SPACE ---
{
.wait
            LDA #&62            ; SPACE key
            STA VIA_ORA_NH
            BIT VIA_ORA_NH
            BPL wait
}

    ; --- Clear screen memory and blank display ---
        LDA #&01 : STA CRTC_ADDR
        LDA #&00 : STA CRTC_DATA  ; Blank display
{
            LDA #&00
            TAX
.clear_src
            STA &3000,X
            DEX
            BNE clear_src
            INC clear_src + 2
            BPL clear_src       ; Loop &3000-&7FFF
}

    ; --- Load game files and start ---
        LDX #LO(oscli_load_gcode)
        LDY #HI(oscli_load_gcode)
        JSR OSCLI               ; *LOAD Gcode

        LDX #LO(oscli_load_fastio)
        LDY #HI(oscli_load_fastio)
        JSR OSCLI               ; *LOAD FastI/O 5800

        JMP &48A0               ; Start the game

.oscli_load_data2
        EQUS "L.Data2", 13
.oscli_load_gcode
        EQUS "L.Gcode", 13
.oscli_load_fastio
        EQUS "L.FastI/O 5800", 13
}