## How it works
-Explain how your project works
+This generates VGA output for a munching squares animation plus some
+other stuff, and some simple music. It uses the VGA and audio PMODs
+listed below.
+
+### LFSR
+
+To provide noise, there is an 11-bit LFSR. It uses the XNOR type,
+shifting right, with taps on bits 0 and 2. Bits 0-5 are tapped to
+provide a noise channel and randomized video noise dithering.
+
+### Video
+
+The video output is the standard 640x480 @ 60Hz, using a 25.175MHz pixel
+clock.
+
+### Audio
+
+Audio comes from a basic PSG. There are four channels of sound based on
+12-bit timers - three pulse channels and one noise channel. The only
+real difference between a pulse channel and a noise channel is that the
+pulse channel flips state when the timer counts down, and the noise
+channel takes a random state from the LFSR. Each channel also has a
+two-bit volume level.
+
+The 25.175MHz clock is divided by a 6-bit counter to create a 393KHz PWM
+output. 6-bits gives 64 possible levels. The PWM output is a simple sum
+of the four channels' volumes at any given instant.
+
+The four channels are sequenced through a sequencer that provides note
+and volume data to the PSG. The sequencer is clocked by dividing VSYNC
+by 6, so the sequencer moves through pattern rows at 10Hz, or 600 ticks
+per minute. Each pattern of 16 ticks represents one measure, four beats,
+which means the music proceeds at 150 BPM.
+
+The sequencer cycles through pre-programmed patterns of notes. Volumes
+are modulated through a single repeating pattern per channel, indexed
+from the sequencer clock divider.
+
+### Text Generator
+
+On-screen text uses a segmented approach, where each segment is defined
+by a mathematical description of a line segment. Each character is
+defined by which segments are off or on, like a multi-segment LED
+display. So text is generated at full resolution despite its large size;
+each character is 50x100 pixels.
## How to test
-Explain how to use your project
+Set the input clock for 25.175MHz. The Pico/RP2040 can output 25.177MHz on
+GPOUT0 with a 125MHz main clock and a divider of 4 [integer part] and
+247 [fractional part]. This worked on my TV.
+
+Reset, and enjoy. :)
## External hardware
- [Leo's VGA PMOD](https://github.com/mole99/tiny-vga)
+- [Tiny Tapeout Audio Pmod](https://github.com/MichaelBell/tt-audio-pmod)