u/realmcalec

Hey! Last time I showed Recaster Pico as a screenshot - here's the real thing on my desk: one RP2040 running a small desktop OS in its 264 KB of SRAM, now with the parts that make it feel like a computer. Yeah, it is still multi-user and multi-tasking (preemptive). No Linux/Unix, no RISC OS.

What's on the board now

• VGA, 640×480 at 60 Hz, 256 colors (RGB332), straight from PIO and DMA. Core 1 composes every scanline just in time.
• A 3.2" SPI touch LCD as a second screen. It mirrors the VGA desktop (well, 1/4 of it ;-)) - core 1 hands the lines it has just composed to a DMA channel, no second compose - or a program takes it over and draws on it directly. Touch moves and clicks the mouse pointer, and the panel also works alone, without a monitor.
• USB keyboard and mouse through a second RP2040 in the serial line: USB host on its micro-USB port, plus a USB-A socket on two GPIOs driven by Pico-PIO-USB. Events travel as CRC-protected packets mixed into the 1 Mbaud UART console, and the serial terminal still works through it. German layout with dead keys and umlauts.
• RTC and EEPROM (DS1307 / AT24C32) on I2C, set up with a small text file - the EEPROM even shows up as a file under /dev.
• GPIO, ADC, PWM, PIO and DMA from the shell language, with the same names as in the Pico SDK.
• Runs from a power bank.

Lessons for your own projects

1. pico_minimize_runtime() turns float off. Pico-PIO-USB computes its PIO clock dividers in float at init, so every float operation hits the SDK's panic stub and core 1 silently stops. Use pico_minimize_runtime(target INCLUDE FLOAT).
2. The same function with pico_multicore: malloc's auto-init mutex never gets initialized, so the first malloc on core 1 hangs forever. PICO_USE_MALLOC_MUTEX=0 if you only malloc once at start.
3. TinyUSB 0.18 drives one host controller per firmware, and Pico-PIO-USB 0.7 no longer enumerates devices on its own. A second USB port means writing a small host on its low-level API - about 300 lines for boot keyboards and mice.
4. Flash erases switch core 0's interrupts off for ~45 ms per sector, while at 1 Mbaud the UART's 32-byte FIFO holds about 10 ms of mouse traffic. Put the UART interrupt on core 1 and run it from SRAM.

Next: sound (the speaker is already on the board), the SD card (already there), and touch-friendly UI controls - buttons, sliders, lists.

And yes: I will post a video of it showing it in motion, soon. And you will get your fingers at that ".uf2"-files to play with it.

A few months back I built the DatCube 82 - a fictional 1982 workstation with its own ISA, an OS written in its own assembly, and a JS emulator. Fun project, but it never quite took off, and I think I know why: there was no real machine you could hold. This is the fix. Same spirit, new target: real silicon, the whole Raspberry Pi Pico family - RP2040, RP2350 (ARM), and RP2350 in RISC-V mode. And I am creating an OS for it! Yeeeeah!

I call it "RECASTER PICO".

The video shows the graphics engine's feature demo (this is from a browser window, but it runs on a VGA screen as well via real hardware (I will show you, soon)! Everything on screen is drawn by one user-space task running in a deterministic register VM (custom ISA, no DIV (for now!), no arithmetic shift - the demo does its 3D math with Q7 sine tables and bias-trick shifts), on a budget of 100,000 VM ops per frame. It uses ~90k. What you're looking at, bottom layer to top:

• Matrix rain on the 80×60 character generator - "ground" cells with transparent backgrounds, so sprites shine through between glyphs
• a 1-bpp city skyline and a spinning wireframe cube on the 1-bit pixel layer (640x480)
• the main attraction: the winding gradient column plus the dark ribbon orbiting it, drawn with nothing but the engine's newest feature - two overlay segments per scanline (per line: two x-spans + two colors, palette index or raw RGB332). The ribbon does hidden-line clipping against the column silhouette with a single span per row. The banding isn't a shader - it's the RGB332 color system doing what it does
• 16 of the 128 sprites as color-cycling orbs, split across two render levels (half in front of everything, half behind the text ink)
• a smooth-scrolling text row at the bottom: the text-offset register is read per scanline, so flipping it at the right beam position gives one row true sub-cell scrolling - a raster split, the register only has 16 values

The OS around it (preemptive multitasking, windows, a terminal with pipes, a tiny flash filesystem, the desktop) is a story for a follow-up post - including the browser emulator so you can run all of it without hardware, or of course WITH IT, if you have a Pi Pico. ;-)

Hab meiner Freundin head&shoulders gekauft als Geburtstagsgeschenk. Sie sagte mir, dass sie alle "APPLE"-Produkte mag, aber bitte keine Süßigkeiten! Nun ja, im lokalen EDEKA hier war das hier das einzige Produkt, was dem Wunsch entsprach. Leider fand sie das nicht witzig. :( Nun ist wohl Schluss.
Zusatzfrage für Leute, die es prüfen können: Ist das eigentlich für Fische geeignet? Ich meine wegen "SCHUPPEN-SCHUTZ²", steht ja da.