add doc for VERA chip

2022-03-22 00:16:19 -05:00 · 2022-03-22 00:16:19 -05:00 · 2589709d1a
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+# VERA
+
+this is a video and sound generator chip used in the Commander X16, a modern 8-bit computer created by The 8-Bit Guy.
+it has 16 channels of pulse/triangle/saw/noise and one stereo PCM channel.
+
+currently Furnace does not support the PCM channel's stereo mode, though.
+
+# effects
+
+- `20xx`: set waveform. the following values are accepted:
+  - 0: pulse
+  - 1: saw
+  - 2: triangle
+  - 3: noise
+- `22xx`: set duty cycle. `xx` may go from 0 to 3F.