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dos33fsprogs/electric_duet/duet.s

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; ***************************************************************************
; * 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 *!*
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