Building a 24-bit arcade CRT display adapter from scratch

7 days ago

Frank and the author acquired an arcade machine (RCade) with a CRT display, initially driven by a Raspberry Pi.
The CRT required a custom solution due to its non-standard resolution (336x262) and the need for better color depth than the Pi's 18-bit.
The author decided to build a USB-connected CRT display adapter to interface with a more powerful computer.
VGA protocol basics were explained, detailing how it syncs with CRT displays using R, G, B, HSYNC, and VSYNC signals.
First attempt used an RP2040 microcontroller with PIO for precise VGA signal generation, achieving a proof-of-concept but limited by USB FS speed (11 Mbps).
Discovered the GUD kernel module, a USB display adapter protocol, and adapted it for the project, improving compatibility and efficiency.
Switched to an STM32H723 for USB HS support but faced issues requiring an external PHY, leading to a redesign with STM32H750IBT.
Final board design included USB HS, VGA output, 8-bit DACs, and HyperRAM, with meticulous routing for signal integrity.
Successfully demonstrated the adapter in the RCade, achieving 24-bit color and 60 Hz refresh rate, a significant improvement.
Future improvements include audio support, better buffering, and protocol documentation.

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