875 Siliconimist Demoscene
875 : Siliconimist Demoscene
- Author: John Cole - Siliconimist
- Description: Bouncing Siliconimist logo on rasterbars with Korobeiniki chiptune
- GitHub repository
- Open in 3D viewer
- Open in VGA Playground
- Clock: 25175000 Hz
How it works
The Siliconimist demo is a 1x1-tile demoscene entry built on the VGA Playground "Logo" preset. It drives a 640x480 @ 60 Hz signal on the TinyVGA Pmod and a 1-bit square-wave chiptune on the TT Audio Pmod.
You can preview the demo and listen to the music here on the VGA Playground!
- A 128x128 bitmap ROM holds a 1-bit Siliconimist sprite: a silicon wafer (circle with an 8x8 grid of die outlines) above a "SILICONIMIST" wordmark.
- The sprite bounces around the screen, ricocheting off all four edges. Each bounce advances a 3-bit color index that recolors the sprite ink from an 8-entry palette.
- Behind the sprite, 16-pixel-tall rasterbars cycle vertically once per frame, picking colors from the same palette indexed by
pix_y[6:4] + frame_counter[5:3]. - A single-note square-wave melody (
chiptune.v) plays Korobeiniki from a 96-step eighth-note ROM (16 frames per step at ~60 Hz VGA). Half-period divides the 25.175 MHz pixel clock to about the right pitch; the driver toggles continuously (not multiplexed scanline bursts), which matches simulation playback (test.capture_audio) and behaves like classic 1-bit PSG audio. Pitch changes reset phase to reduce clicks. Holdui[2]low for sound; mute tiesuio_out[7]low.
How to test
- Plug a TinyVGA Pmod (mole99/tiny-vga) into the dedicated-output Pmod bank and connect a VGA monitor.
- Plug a TT Audio Pmod (MichaelBell/tt-audio-pmod) into the bidirectional Pmod bank — its input is on
uio[7]. - Pulse
rst_nlow briefly. The Siliconimist sprite should appear bouncing on a moving rasterbar background; the Pmod should play Korobeiniki (Tetris theme) on a loop. - Toggle
ui[1]to enable per-bounce color cycling (otherwise the sprite is white). - Toggle
ui[0]to tile the sprite full-screen (handy for confirming the bitmap data). - Hold
ui[2]high to mute the audio output.
External hardware
The pinout follows the official Tiny Tapeout pinouts spec:
- VGA: TinyVGA Pmod on the dedicated output bank
uo[7:0](mole99/tiny-vga). - Audio: TT Audio Pmod with mono input on
uio[7](MichaelBell/tt-audio-pmod). The lower bidirectional pinsuio[6:0]are tied low / disabled, leaving the Pmod's pass-through row free for compatibility.
More In-Depth Writeup
Follow along at the the Siliconimist podcast and blog here and hear our more dramatic, in-depth writeup about the design and our journey to a first tapeout!
IO
| # | Input | Output | Bidirectional |
|---|---|---|---|
| 0 | cfg_tile (tiles the logo) | R1 | |
| 1 | G1 | ||
| 2 | mute (mutes the audio) | B1 | |
| 3 | vsync | ||
| 4 | R0 | ||
| 5 | G0 | ||
| 6 | B0 | ||
| 7 | hsync | PWM audio out |