; *************************************************************************** ; * Copyright (C) 1979-2015 by Paul Lutus * ; * http://arachnoid.com/administration * ; * * ; * This program is free software; you can redistribute it and/or modify * ; * it under the terms of the GNU General Public License as published by * ; * the Free Software Foundation; either version 2 of the License, or * ; * (at your option) any later version. * ; * * ; * This program is distributed in the hope that it will be useful, * ; * but WITHOUT ANY WARRANTY; without even the implied warranty of * ; * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * ; * GNU General Public License for more details. * ; * * ; * You should have received a copy of the GNU General Public License * ; * along with this program; if not, write to the * ; * Free Software Foundation, Inc., * ; * 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. * ; *************************************************************************** ; Electric Duet Player Routine circa 1980 ; Most comments added by Vince Weaver .define EQU = ; These are all "Free" zero page locations FREQ1 EQU $06 FREQ2 EQU $07 DURATION EQU $08 INSTRUMENT1 EQU $09 INSTRUMENT2 EQU $1D MADDRL EQU $1E MADDRH EQU $1F LOC4E EQU $4E COUNT256 EQU $4F play_ed: LDA #$01 ; 900: A9 01 ; 2 *!* STA INSTRUMENT1 ; 902: 85 09 ; 3 set default STA INSTRUMENT2 ; 904: 85 1D ; 3 instruments PHA ; 906: 48 ; 3 1 on stack PHA ; 907: 48 ; 3 1 on stack PHA ; 908: 48 ; 3 1 on stack BNE load_triplet ; 909: D0 15 ; 4 *!* start decoding change_instrmnt: INY ; 90B: C8 ; 2 LDA (MADDRL),Y ; 90C: B1 1E ; 5 *!* load next byte STA INSTRUMENT1 ; 90E: 85 09 ; 3 save instrument INY ; 910: C8 ; 2 LDA (MADDRL),Y ; 911: B1 1E ; 5 *!* load next byte STA INSTRUMENT2 ; 913: 85 1D ; 3 save instrument triplet_loop: LDA MADDRL ; 915: A5 1E ; 3 *!* increment pointer CLC ; 917: 18 ; 2 by three ADC #$03 ; 918: 69 03 ; 2 *!* STA MADDRL ; 91A: 85 1E ; 3 BCC load_triplet ; 91C: 90 02 ; 4 *!* if overflow INC MADDRH ; 91E: E6 1F ; 5 update high byte load_triplet: LDY #$00 ; 920: A0 00 ; 2 *!* Set Y to zero LDA (MADDRL),Y ; 922: B1 1E ; 5 *!* Load first byte CMP #$01 ; 924: C9 01 ; 2 Compare to 1 BEQ change_instrmnt ; 926: F0 E3 ; 4 *!* If one change inst BCS play_note ; 928: B0 0D ; 4 *!* If >1, then duration PLA ; 92A: 68 ; 4 pop off stack PLA ; 92B: 68 ; 4 pop off stack PLA ; 92C: 68 ; 4 pop off stack ; fallthrough if first byte was zero ; Load byte from music stream ; Set X=EOR if note zero, set X=CMP if it is load_freq: LDX #$49 ; 92D: A2 49 ; 2 *!* X=0x49 (EOR opcode) INY ; 92F: C8 ; 2 increment to next byte LDA (MADDRL),Y ; 930: B1 1E ; 5 *!* load next byte BNE exit_player ; 932: D0 02 ; 4 *!* if not zero LDX #$C9 ; 934: A2 C9 ; 2 *!* X=0xC9 (CMP opcode) exit_player: ; if byte0==0 and byte1==0 then done playing RTS ; 936: 60 ; 6 return ; We've got a duration/note/note triplet here play_note: STA DURATION ; 937: 85 08 ; 3 store out duration JSR load_freq ; 939: 20 2D09 ; 6 get freq#1 STX selfmodify1 ; 93C: 8E 8309 ; 4 if 0 self-modify EOR/CMP STA FREQ1 ; 93F: 85 06 ; 3 LDX INSTRUMENT1 ; 941: A6 09 ; 3 *!* instr1_adjust: LSR A ; 943: 4A ; 2 rshift freq by inst# DEX ; 944: CA ; 2 BNE instr1_adjust ; 945: D0 FC ; 4 *!* STA selfmodify2+1 ; 947: 8D 7C09 ; 4 self-modify a CPY JSR load_freq ; 94A: 20 2D09 ; 6 get freq#2 STX selfmodify3 ; 94D: 8E BB09 ; 4 if 0 self-modify EOR/CMP STA FREQ2 ; 950: 85 07 ; 3 LDX INSTRUMENT2 ; 952: A6 1D ; 3 *!* instr2_adjust: LSR A ; 954: 4A ; 2 rshift freq by inst# DEX ; 955: CA ; 2 BNE instr2_adjust ; 956: D0 FC ; 4 *!* STA selfmodify4+1 ; 958: 8D B409 ; 4 self modify a CPX PLA ; 95B: 68 ; 4 TAY ; 95C: A8 ; 2 PLA ; 95D: 68 ; 4 TAX ; 95E: AA ; 2 PLA ; 95F: 68 ; 4 BNE label8 ; 960: D0 03 ; 4 *!* label99: BIT $C030 ; 962: 2C 30C0 ; 4 SPEAKER label8: CMP #$00 ; 965: C9 00 ; 2 BMI label7 ; 967: 30 03 ; 4 *!* NOP ; 969: EA ; 2 BPL label9 ; 96A: 10 03 ; 4 *!* label7: BIT $C030 ; 96C: 2C 30C0 ; 4 SPEAKER label9: STA LOC4E ; 96F: 85 4E ; 3 BIT $C000 ; 971: 2C 00C0 ; 4 KEYBOARD DATA BMI exit_player ; 974: 30 C0 ; 4 *!* if keypress, exit DEY ; 976: 88 ; 2 BNE selfmodify2 ; 977: D0 02 ; 4 *!* BEQ label11 ; 979: F0 06 ; 4 *!* selfmodify2: CPY #$00 ; 97B: C0 00 ; 2 BEQ selfmodify1 ; 97D: F0 04 ; 4 *!* !!! BNE label13 ; 97F: D0 04 ; 4 *!* label11: LDY FREQ1 ; 981: A4 06 ; 3 *!* selfmodify1: EOR #$40 ; 983: 49 40 ; 2 *!* !!! label13: BIT LOC4E ; 985: 24 4E ; 3 BVC label14 ; 987: 50 07 ; 4 *!* BVS label15 ; 989: 70 00 ; 4 *!* label15: BPL label16 ; 98B: 10 09 ; 4 *!* NOP ; 98D: EA ; 2 BMI label17 ; 98E: 30 09 ; 4 *!* label14: NOP ; 990: EA ; 2 BMI label16 ; 991: 30 03 ; 4 *!* NOP ; 993: EA ; 2 BPL label17 ; 994: 10 03 ; 4 *!* label16: CMP $C030 ; 996: CD 30C0 ; 4 SPEAKER label17: DEC COUNT256 ; 999: C6 4F ; 5 div by 256 counter BNE label18 ; 99B: D0 11 ; 4 *!* DEC DURATION ; 99D: C6 08 ; 5 BNE label18 ; 99F: D0 0D ; 4 *!* BVC label19 ; 9A1: 50 03 ; 4 *!* BIT $C030 ; 9A3: 2C 30C0 ; 4 SPEAKER label19: PHA ; 9A6: 48 ; 3 TXA ; 9A7: 8A ; 2 PHA ; 9A8: 48 ; 3 TYA ; 9A9: 98 ; 2 PHA ; 9AA: 48 ; 3 JMP triplet_loop ; 9AB: 4C 1509 ; 3 label18: DEX ; 9AE: CA ; 2 BNE selfmodify4 ; 9AF: D0 02 ; 4 *!* BEQ label21 ; 9B1: F0 06 ; 4 *!* selfmodify4: CPX #$00 ; 9B3: E0 00 ; 2 BEQ selfmodify3 ; 9B5: F0 04 ; 4 *!* !!! BNE label23 ; 9B7: D0 04 ; 4 *!* label21: LDX FREQ2 ; 9B9: A6 07 ; 3 *!* selfmodify3: EOR #$80 ; 9BB: 49 80 ; 2 *!* !!! label23: BVS label99 ; 9BD: 70 A3 ; 4 *!* NOP ; 9BF: EA ; 2 BVC label8 ; 9C0: 50 A3 ; 4 *!*