80-column colour text?

[thejpster]

I've recently shown it's possible to produce 80 column colour text on a Pico with only a mild overclock to 151.2 MHz (6x the 25.2 MHz VGA pixel clock).

I have GPL3 licensed PIO assembler and Rust source code at https://github.com/Neotron-Compute/Neotron-Pico-BIOS/blob/faster-text-mode-2/src/vga/mod.rs#L1442-L1503.

The main trick is:

• look up each character in the font to get a glyph
• take the 8 bit slice from that glyph
• cut it into 2-bit pieces
• create a 9-bit index (2 bits for the two pixels, 4 bits for the foreground colour and 3 bits for the background colour) into the table
• Look up in the table giving you a pair of 12-bit (or 16-bit) RGB pixels as the output.
• put that RGB pixel pair (a 32-bit value) into a scanline buffer which is 640 pixels long
• ping-pong two scan-line buffers into the PIO using DMA.

It uses 92% of Core 1 but the picture is solid and Core 0 is free to do ANSI/UART/whatever.

Edit: added photo of the output

[abaffa]

another color terminal using RP2040 is David Hansel's VersaTerm https://github.com/dhansel/VersaTerm

[thejpster]

Looks like it uses hand written assembly and a 151 MHz clock speed for the VGA output, or 252 MHz for the HDMI output. Neat project.