Split YM2610B document

papers/doc/7-systems/README.md

@@ -10,6 +10,7 @@ this is a list of systems that Furnace supports, including each system's effects
 - [Commodore 64](c64.md)
 - [Arcade (YM2151/PCM)](arcade.md)
 - [Neo Geo/YM2610](ym2610.md)
+- [Taito Arcade/YM2610B](ym2610b.md)
 - [AY-3-8910](ay8910.md)
 - [Amiga](amiga.md)
 - [Yamaha YM2612 standalone](ym2612.md)

papers/doc/7-systems/ym2610.md

@@ -4,8 +4,6 @@ originally an arcade board, but SNK shortly adapted it to a rather expensive vid
 
 its soundchip is a 3-in-1: FM, YM2149 (AY-3-8910 clone) and ADPCM in a single package!
 
-YM2610B variant is YM2610 with 2 extra FM channels, it's mainly used at some 90s Taito Arcade hardwares.
-
 # effects
 
 - `10xy`: set LFO parameters.

papers/doc/7-systems/ym2610b.md

@@ -0,0 +1,57 @@
+# Taito Arcade/Yamaha YM2610
+
+YM2610B is basically YM2610 with 2 extra FM channels used at some 90s Taito Arcade hardwares.
+
+# effects
+
+- `10xy`: set LFO parameters.
+  - `x` toggles the LFO.
+  - `y` sets its speed.
+- `11xx`: set feedback of channel.
+- `12xx`: set operator 1 level.
+- `13xx`: set operator 2 level.
+- `14xx`: set operator 3 level.
+- `15xx`: set operator 4 level.
+- `16xy`: set multiplier of operator.
+  - `x` is the operator (1-4).
+  - `y` is the mutliplier.
+- `18xx`: toggle extended channel 2 mode.
+  - 0 disables it and 1 enables it.
+  - only in extended channel 2 system.
+- `19xx`: set attack of all operators.
+- `1Axx`: set attack of operator 1.
+- `1Bxx`: set attack of operator 2.
+- `1Cxx`: set attack of operator 3.
+- `1Dxx`: set attack of operator 4.
+- `20xx`: set SSG channel mode. `xx` may be one of the following:
+  - `00`: square
+  - `01`: noise
+  - `02`: square and noise
+  - `03`: nothing (apparently)
+  - `04`: envelope and square
+  - `05`: envelope and noise
+  - `06`: envelope and square and noise
+  - `07`: nothing
+- `21xx`: set noise frequency. `xx` is a value between 00 and 1F.
+- `22xy`: set envelope mode.
+  - `x` sets the envelope shape, which may be one of the following:
+    - `0: \___` decay
+    - `4: /___` attack once
+    - `8: \\\\` saw
+    - `9: \___` decay
+    - `A: \/\/` inverse obelisco
+    - `B: \¯¯¯` decay once
+    - `C: ////` inverse saw
+    - `D: /¯¯¯` attack
+    - `E: /\/\` obelisco
+    - `F: /___` attack once
+  - if `y` is 1 then the envelope will affect this channel.
+- `23xx`: set envelope period low byte.
+- `24xx`: set envelope period high byte.
+- `25xx`: slide envelope period up.
+- `26xx`: slide envelope period down.
+- `29xy`: enable SSG auto-envelope mode.
+  - in this mode the envelope period is set to the channel's notes, multiplied by a fraction.
+  - `x` is the numerator.
+  - `y` is the denominator.
+  - if `x` or `y` are 0 this will disable auto-envelope mode.