WIP SNES support, part 1

papers/doc/7-systems/README.md

@@ -34,5 +34,6 @@ this is a list of systems that Furnace supports, including each system's effects
 - [Konami VRC6](vrc6.md)
 - [Famicom Disk System](fds.md)
 - [Nintendo MMC5](mmc5.md)
+- [SNES](snes.md)
 
 Furnace also reads .dmf files with the [Yamaha YMU759](ymu759.md) system, but...

papers/doc/7-systems/snes.md

@@ -0,0 +1,18 @@
+# Super NES
+
+The successor to NES to compete with Genesis. Now packing with superior graphics and sample-based audio. Also known as Super Famicom.
+
+Its audio subsystem, developed by Sony, features the DSP chip, SPC700 microcontroller and 64KB of dedicated SRAM used by both. This whole system itself is pretty much a separate computer that the main CPU needs to upload its program and samples to.
+
+The DSP chip can
+
+Furnace communicates with the DSP directly and provide a full 64KB memory. This memory might be reduced excessively on ROM export to make up for playback engine and pattern data.
+
+# effects
+
+Note: this chip has a signed left/right level. Which can be used for inverted (surround) stereo. A signed 8-bit value means 80 - FF = -128 - -1. Other values work normally. A value of -128 is not recommended as it could cause overflows.
+
+- `10xx`: Set echo feedback level. This effect will apply to all channels.
+- `11xx`: Set echo left level (signed 8-bit). This effect will apply to all channels.
+- `12xx`: Set echo right level (signed 8-bit). This effect will apply to all channels.
+- `13xx`: Set the length of the echo delay buffer. This will also affect the size of the sample RAM!