openfpga-varvara

A core for Analogue Pocket that is an early work-in-progress FPGA implementation of Varvara / Uxn by Hundred Rabbits.

Screenshots

Running the core on an Analogue Pocket

Unzip the latest core from the Releases section, and copy + merge the Assets, Cores, and Platforms folders to your Analogue Pocket SD Card.

Specs

• Display: 320x288 at 60Hz
• CPU: 44.411586 MHz
• Main RAM: 64 KB
• Stack RAM: 2x 256 bytes
• Device RAM: 256 bytes

Known issue on Analogue OS 2.0 (Fixed in 2.1)

If you see a black screen after loading a ROM, the ROM is likely actually still running. Sometimes you need to open Core Settings -> Display Mode, and re-select a display mode, to see video output. This was a bug on Analogue's end. Upgrading to AnalogueOS 2.1 or above fixes this issue.

Known issue on Analogue OS <= 2.1 (Fixed in 2.2)

ROMs may need to be padded with additional empty bytes (0x00) to be an even multiple of 4 bytes. Updating to Analogue OS 2.2 fixes this issue.

Limitations and other Known Issues

Many Varvara device features aren't implemented:

• audio
• keyboard
• file system
• console

ROMs larger than 65280 bytes probably won't work, because only the first 64KB is loaded into RAM, and there is no expansion memory support.

Test ROMs

I added some test ROMs into the dist/assets folder. Some of these are slightly modified examples from the Uxn Chibicc fork example code:

• bounce.rom - bouncing square demo
• fill_test.rom - draws a pattern of fills from bottom-right and then top-left
• mandelbrot.rom - draws a Mandelbrot, vertical line-by-line
• cube3d.rom - draws a spinning 3D wireframe cube

Building the core yourself (optional)

Building the RBF

Windows / Linux:

Quartus Lite App: Use Quartus Lite Edition to open the project at src/fpga/ap_core.qpf and build.

Command line (example):

~/altera_lite/24.1std/quartus/bin/quartus_sh --flow compile src/fpga/ap_core.qpf

macOS:

Use a Docker Quartus image to build:

Clean (example command using a Docker Quartus Image):

docker run --platform linux/amd64 -t --rm -v $(pwd):/build didiermalenfant/quartus:22.1-apple-silicon quartus_sh --clean ap_core.qpf  

Build (example command using a Docker Quartus Image):

docker run --platform linux/amd64 -t --rm -v $(pwd):/build didiermalenfant/quartus:22.1-apple-silicon quartus_sh --flow compile ap_core.qpf

Reversing the RBF

The resulting bitstream at output_files/ap_core.rbf will need to be reversed into a bitstream.rbf_r file, before running on a Pocket.

See Creating a reversed RBF for more details.