Raspberry Pi Pico

Lumen’s VM runs bare-metal on the Raspberry Pi Pico, built against pico-sdk with devkitPro/CMake toolchains. There’s no compiler on-device — you write and compile .lmn programs on desktop, then get the resulting .bin bytecode onto the Pico.

What’s ported

The Pico build reuses the same execute() loop as desktop (see The Virtual Machine), with two structural differences:

• funcTable instead of funcMap. Desktop’s native function table is a std::map-backed set of lambdas; the Pico build uses a plain array of NativeFn function pointers, since embedded C++ toolchains make heavier STL containers more expensive than they’re worth here.
• A GPIO-specific EXEC range. Function indices 0xD0–0xFF are reserved on Pico for application-specific native functions — GPIO writes, I2C calls, and similar host behavior — mapped onto the tail end of funcTable at a fixed offset from the base opcode. Desktop programs don’t use this range at all; it only means something once bytecode is destined for a Pico.

Getting bytecode onto the device

1. Write and compile your .lmn program on desktop as usual (lumen program.lmn --compile), producing a .bin file — see CLI Reference.
2. Cross-compile the Pico firmware image, embedding the .bin bytecode as a C byte array baked into the binary (rather than reading from a filesystem, which the Pico doesn’t have in the general case).
3. Flash the resulting .uf2 image onto the Pico over USB in bootloader mode, the same way you’d flash any other pico-sdk project.

Peripheral access

Programs that need to touch hardware — an I2C display, a GPIO pin, a UART line — do so through native functions registered in the 0xD0–0xFF range, exactly like any other built-in from the language’s point of view: a compiled EXEC call with a function index. From inside a .lmn program, a GPIO write looks like any other built-in call; the fact that it’s toggling a physical pin rather than printing to a terminal is entirely a property of what’s registered in funcTable on that build, not something the language syntax needs to know about.