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duet: more comments
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Vince Weaver
parent
721e96a864
commit
741ab4c1a1
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@ -20,50 +20,54 @@
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; Electric Duet Player Routine circa 1980
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; Most comments added by Vince Weaver
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.define EQU =
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; These are all "Free" zero page locations
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FREQ1 EQU $06
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FREQ2 EQU $07
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FREQ1 EQU $06
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FREQ2 EQU $07
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DURATION EQU $08
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LOC9 EQU $09
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LOC1D EQU $1D
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MADDRL EQU $1E
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MADDRH EQU $1F
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LOC4E EQU $4E
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LOC4F EQU $4F
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INSTRUMENT1 EQU $09
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INSTRUMENT2 EQU $1D
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MADDRL EQU $1E
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MADDRH EQU $1F
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LOC4E EQU $4E
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COUNT256 EQU $4F
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STARTADDR EQU $0900
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play_ed:
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LDA #$01 ; 900: A9 01 ; 2 *!*
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STA LOC9 ; 902: 85 09 ; 3
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STA LOC1D ; 904: 85 1D ; 3
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STA INSTRUMENT1 ; 902: 85 09 ; 3 set default
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STA INSTRUMENT2 ; 904: 85 1D ; 3 instruments
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PHA ; 906: 48 ; 3 1 on stack
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PHA ; 907: 48 ; 3 1 on stack
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PHA ; 908: 48 ; 3 1 on stack
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BNE load_triplet ; 909: D0 15 ; 4 *!*
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BNE load_triplet ; 909: D0 15 ; 4 *!* start decoding
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label2:
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change_instrmnt:
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INY ; 90B: C8 ; 2
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LDA (MADDRL),Y ; 90C: B1 1E ; 5 *!*
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STA LOC9 ; 90E: 85 09 ; 3
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LDA (MADDRL),Y ; 90C: B1 1E ; 5 *!* load next byte
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STA INSTRUMENT1 ; 90E: 85 09 ; 3 save instrument
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INY ; 910: C8 ; 2
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LDA (MADDRL),Y ; 911: B1 1E ; 5 *!*
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STA LOC1D ; 913: 85 1D ; 3
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loop:
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LDA MADDRL ; 915: A5 1E ; 3 *!*
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CLC ; 917: 18 ; 2
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LDA (MADDRL),Y ; 911: B1 1E ; 5 *!* load next byte
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STA INSTRUMENT2 ; 913: 85 1D ; 3 save instrument
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triplet_loop:
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LDA MADDRL ; 915: A5 1E ; 3 *!* increment pointer
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CLC ; 917: 18 ; 2 by three
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ADC #$03 ; 918: 69 03 ; 2 *!*
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STA MADDRL ; 91A: 85 1E ; 3
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BCC load_triplet ; 91C: 90 02 ; 4 *!*
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INC MADDRH ; 91E: E6 1F ; 5
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BCC load_triplet ; 91C: 90 02 ; 4 *!* if overflow
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INC MADDRH ; 91E: E6 1F ; 5 update high byte
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load_triplet:
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LDY #$00 ; 920: A0 00 ; 2 *!* Set Y to zero
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LDA (MADDRL),Y ; 922: B1 1E ; 5 *!* Load first byte
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CMP #$01 ; 924: C9 01 ; 2 Compare to 1
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BEQ label2 ; 926: F0 E3 ; 4 *!* If one ?
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BEQ change_instrmnt ; 926: F0 E3 ; 4 *!* If one change inst
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BCS play_note ; 928: B0 0D ; 4 *!* If >1, then duration
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PLA ; 92A: 68 ; 4 pop off stack
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PLA ; 92B: 68 ; 4 pop off stack
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@ -74,7 +78,7 @@ load_triplet:
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; Load byte from music stream
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; Set X=EOR if note zero, set X=CMP if it is
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sub1:
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load_freq:
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LDX #$49 ; 92D: A2 49 ; 2 *!* X=0x49 (EOR opcode)
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INY ; 92F: C8 ; 2 increment to next byte
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LDA (MADDRL),Y ; 930: B1 1E ; 5 *!* load next byte
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@ -90,31 +94,34 @@ exit_player:
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play_note:
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STA DURATION ; 937: 85 08 ; 3 store out duration
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JSR sub1 ; 939: 20 2D09 ; 6 get freq#1
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JSR load_freq ; 939: 20 2D09 ; 6 get freq#1
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STX STARTADDR+$83 ; 93C: 8E 8309 ; 4 if 0 self-modify EOR/CMP
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STA FREQ1 ; 93F: 85 06 ; 3 ??
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LDX LOC9 ; 941: A6 09 ; 3 *!* ??
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label5:
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LSR A ; 943: 4A ; 2
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DEX ; 944: CA ; 2
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BNE label5 ; 945: D0 FC ; 4 *!*
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STA STARTADDR+$7C ; 947: 8D 7C09 ; 4 ; self-modify
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STA FREQ1 ; 93F: 85 06 ; 3
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LDX INSTRUMENT1 ; 941: A6 09 ; 3 *!*
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JSR sub1 ; 94A: 20 2D09 ; 6 get freq#2
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instr1_adjust:
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LSR A ; 943: 4A ; 2 rshift freq by inst#
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DEX ; 944: CA ; 2
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BNE instr1_adjust ; 945: D0 FC ; 4 *!*
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STA STARTADDR+$7C ; 947: 8D 7C09 ; 4 self-modify a CPY
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JSR load_freq ; 94A: 20 2D09 ; 6 get freq#2
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STX STARTADDR+$BB ; 94D: 8E BB09 ; 4 if 0 self-modify EOR/CMP
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STA FREQ2 ; 950: 85 07 ; 3
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LDX LOC1D ; 952: A6 1D ; 3 *!*
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label6:
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LSR A ; 954: 4A ; 2
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LDX INSTRUMENT2 ; 952: A6 1D ; 3 *!*
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instr2_adjust:
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LSR A ; 954: 4A ; 2 rshift freq by inst#
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DEX ; 955: CA ; 2
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BNE label6 ; 956: D0 FC ; 4 *!*
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STA STARTADDR+$B4 ; 958: 8D B409 ; 4 ; self-modify
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BNE instr2_adjust ; 956: D0 FC ; 4 *!*
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STA STARTADDR+$B4 ; 958: 8D B409 ; 4 self modify a CPX
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PLA ; 95B: 68 ; 4
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TAY ; 95C: A8 ; 2
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PLA ; 95D: 68 ; 4
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TAX ; 95E: AA ; 2
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PLA ; 95F: 68 ; 4
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BNE label8 ; 960: D0 03 ; 4 *!*
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label99:
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BIT $C030 ; 962: 2C 30C0 ; 4 SPEAKER
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label8:
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@ -155,8 +162,9 @@ label14:
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label16:
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CMP $C030 ; 996: CD 30C0 ; 4 SPEAKER
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label17:
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DEC LOC4F ; 999: C6 4F ; 5
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DEC COUNT256 ; 999: C6 4F ; 5 div by 256 counter
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BNE label18 ; 99B: D0 11 ; 4 *!*
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DEC DURATION ; 99D: C6 08 ; 5
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BNE label18 ; 99F: D0 0D ; 4 *!*
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BVC label19 ; 9A1: 50 03 ; 4 *!*
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@ -167,7 +175,7 @@ label19:
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PHA ; 9A8: 48 ; 3
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TYA ; 9A9: 98 ; 2
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PHA ; 9AA: 48 ; 3
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JMP loop ; 9AB: 4C 1509 ; 3
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JMP triplet_loop ; 9AB: 4C 1509 ; 3
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label18:
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DEX ; 9AE: CA ; 2
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BNE label20 ; 9AF: D0 02 ; 4 *!*
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