Initial commit

LICENSE

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+MIT License
+
+Copyright (c) 2024 All You Can Execute
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

README.md

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+# Twin ("a literal twin-channeled cover")
+
+This is a source code to the Atari 2600 music demo "Twin". It also contains the
+code for the software pitch driver called TIunA which works by changing between
+two pitch registers at a very fast speed at the right time. It is located in
+main.asm.
+
+Watch the demo [here](https://www.youtube.com/watch?v=5xWEkZSFwKQ). (the main flashy lines are replaced though)
+
+Original song by Petriform. Cover by Abstract 64. Code by Natt.
+
+## Building
+
+Following programs are required:
+- [Furnace 0.6.5](https://github.com/tildearrow/furnace/releases/tag/v0.6.5)
+- [64tass](https://sourceforge.net/projects/tass64/)
+
+Open twin_tia_ayce.fur in Furnace and do a TIunA export as song.asm with these
+parameters:
+- base song label name: twin
+- max size in first bank: 1024
+- max size in other banks: 4048
+
+Then run following commands:
+```
+64tass -C -a -b -o ayce-twin.bin main.asm
+```

hw.asm

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+; a2600 hardware registers
+
+; TIA
+; write
+VSYNC   = $00
+VBLANK  = $01
+WSYNC   = $02
+RSYNC   = $03
+NUSIZ0  = $04
+NUSIZ1  = $05
+COLUP0  = $06
+COLUP1  = $07
+COLUPF  = $08
+COLUBK  = $09
+CTRLPF  = $0a
+REFP0   = $0b
+REFP1   = $0c
+PF0     = $0d
+PF1     = $0e
+PF2     = $0f
+RESP0   = $10
+RESP1   = $11
+RESM0   = $12
+RESM1   = $13
+RESBL   = $14
+AUDC0   = $15
+AUDC1   = $16
+AUDF0   = $17
+AUDF1   = $18
+AUDV0   = $19
+AUDV1   = $1a
+GRP0    = $1b
+GRP1    = $1c
+ENAM0   = $1d
+ENAM1   = $1e
+ENABL   = $1f
+HMP0    = $20
+HMP1    = $21
+HMM0    = $22
+HMM1    = $23
+HMBL    = $24
+VDELP0  = $25
+VDELP1  = $26
+VDELBL  = $27
+RESMP0  = $28
+RESMP1  = $29
+HMOVE   = $2a
+HMCLR   = $2b
+CXCLR   = $2c
+; read
+CXM0P   = $30
+CXM1P   = $31
+CXP0FB  = $32
+CXP1FB  = $33
+CXM0FB  = $34
+CXM1FB  = $35
+CXBLPF  = $36
+CXPPMM  = $37
+INPT0   = $38
+INPT1   = $39
+INPT2   = $3a
+INPT3   = $3b
+INPT4   = $3c
+INPT5   = $3d
+
+; RIOT
+SWCHA   = $0280
+SWACNT  = $0281
+SWCHB   = $0282
+SWBCNT  = $0283
+INTIM   = $0284
+INSTAT  = $0285
+TIM1T   = $0294
+TIM8T   = $0295
+TIM64T  = $0296
+T1024T  = $0297
+
+; 32k bank switches
+BANK0   = $fff4
+BANK1   = $fff5
+BANK2   = $fff6
+BANK3   = $fff7
+BANK4   = $fff8
+BANK5   = $fff9
+BANK6   = $fffa
+BANK7   = $fffb