2 July 2023

ArcDVI is a hardware add-on allowing Acorn Archimedes computers to output video via DVI. Retrocompute on a quality monitor! :)

The ArcDVI project comprises several parts:

• The main PCB, which contains an FPGA and a MCU (on which this firmware runs).
• "VIDC" PCBs: either an interposer that holds VIDC in socketed machines (e.g. A440), or a clip-over board for machines in which VIDC is soldered down (e.g. A3000)
• The FPGA design
• The microcontroller firmware (This repo)
• Optional extension/test software for RISC OS

This firmware is written for the RP2040 microcontroller on the ArcDVI board, and has several duties/features:

• Initialises the video transmitter/serialiser IC over I2C (supports ADV7513, previously TDA19988)
• Programs the iCE40HX FPGA bitstream
• Provides a USB CDC debug console, with commands/debug to control & monitor mode changes and video config
• Provides a register read/write interface to FPGA registers over SPI
• Monitors the VIDC registers for changes, calculates video output timing and reconfigures the FPGA on the fly

The RP2040 is a fun chip, and the USB bootloader makes it easy for field firmware/bitstream upgrades.

In future, the MCU will also perform audio processing for sound support.

Starting at firmware/main.c, a simple top-level loop polls registers that indicate if the VIDC HCR/VCR values have been written (as happens on a mode switch). If so, video.c:video_probe_mode() selects an appropriate output configuration given VIDC's configuration.

Aside from a whole lot of debugging/development features (such as commands.c which provides a super-simple CLI to tweak config via UART console), the core responsibility of the firmware is video_probe_mode().

This project is built using the Raspberry Pi Pico SDK. Configure it like any other pico-sdk project:

[~/ArcDVI-fw]$ mkdir build
[~/ArcDVI-fw]$ cd build
[~/ArcDVI-fw/build]$ cmake .. PICO_SDK_PATH=~/pico-sdk
...(pico-sdk configures)...

The FPGA bitstream is embedded into the MCU firmware. The bitstream must first be built from ArcDVI-hw, and added to the build directory. The firmware can then be built:

[~/ArcDVI-fw/build]$ ln -s ~/ArcDVI-hw/arcdvi-ice40.bit ./fpga.bit
[~/ArcDVI-fw/build]$ make

The output is firmware.uf2. This is usually programmed by putting the RP2040 into bootloader mode and copying the file to the resulting USB MSD.

(This link will probably break eventually, but) There's an ArcDVI thread on the StarDot forums with some photos/development notes: https://stardot.org.uk/forums/viewtopic.php?f=16&t=23772

Copyright 2021-2023 Matt Evans, and provided under the MIT licence.