Ports

A port is the C code that sits under the VM for one chip family: startup, memory map, USB or UART, and the machine bindings. A board is a pinout and a set of compile flags inside that port.

Official ports

Port	Chips	Notes
rp2	RP2040, RP2350	Pico, Pico W, Pico 2. UF2. Strong `machine`.
esp32	ESP32, S2, S3, C3, C5, C6, P4	Wi-Fi / BLE. IDF based.
esp8266	ESP8266	Small heap. Feature level is tight.
stm32	STM32 F0–U5 and friends	pyboard origin. USB CDC. CAN in 1.28.
samd	SAMD21 / SAMD51	Many Adafruit-shaped boards.
nrf	nRF51 / nRF52	micro:bit, BLE-heavy boards.
mimxrt	i.MX RT	Teensy 4 class, lots of RAM.
unix / windows / webassembly	Host OS / WASM	No GPIO. Language + stdlib + embed.
alif, cc3200, renesas-ra, zephyr, qemu, embed, …	Various	See Other. Tiers in 1.27+ say how complete they are.

Adding a board

Inside an existing port you usually add a directory under boards/:

mpconfigboard.h — board name, heap size, which peripherals to compile
mpconfigboard.mk or CMake fragments — CPU variant, linker script
pins.csv or equivalent — named pins for Pin("LED")
Optional manifest.py — frozen modules baked into the image

A new chip family is a new ports/foo/: main.c, mpconfigport.h, a UART for the REPL, a heap, and then machine bindings one class at a time. The developer docs walk through it; embed is the smallest “port” if you only want the VM inside another program.

Tiers

From 1.27 the project labels ports by how complete and how well tested they are. Tier 1 is the daily-driver set (rp2, esp32, stm32, unix, …). Lower tiers still run; they may lag on machine APIs. Check the release notes when a class is missing — it may be the port, not your script.