pico-rv32ima

Running Linux on the RP2040 (and RP2350)

How it works

This project uses CNLohr's mini-rv32ima RISC-V emulator core, adapted into the tiny-rv32ima library to run Linux on a Raspberry Pi Pico (or Pico 2), using SPI PSRAM chips as system memory. The Linux kernel, device tree binary and root filesystem are stored on an SD card.

Features

• No-MMU 32bit RISC-V Linux
• 8 megabytes of RAM
• SD card block device
• VGA text display and PS/2 keyboard support

Requirements

• a Raspberry Pi Pico or Pico 2 (or other RP2040 or RP2350 boards)
• an SD card
• an 8 megabyte (64Mbit) SPI PSRAM chip (LY68L6400 and ESP-PSRAM64H are known to be working).
• (optional, if using the VGA console) 3.3V level shifter for the PS/2 keyboard and a few resistors for the VGA interface.

This project overvolts and overclocks the microcontroller! Use at own risk!

How to use

This project is meant to be used with the official Pi Pico VS Code extension. The configuration and pin mapping can be modified in the hw_config.h and vm_config.h files.

• The SD card operates in SPI mode, with the following default pinout:

  • CLK: GPIO2
  • MISO: GPIO4
  • MOSI: GPIO3
  • CS: GPIO0

• The RAM chips are connected with the following default pinout:

  • CLK: GPIO10
  • MISO: GPIO12
  • MOSI: GPIO11
  • CS: GPIO13

• The VGA display is connected as follows:

  • VSYNC: GPIO16
  • HSYNC: GPIO17
  • R: GPIO18
  • G and B are the next two consecutive pins.
  • the R, G and B lines must be connected through 330 ohm resistors to avoid damage to the monitor

• The PS/2 keyboard data pin is connected to GPIO26 and the clock pin to GPIO27. 5V to 3.3V level shifting must be used between the PS/2 keyboard and the RP2040!

• The system console can also be exposed over USB-CDC or UART. By default, the VGA and USB consoles are active. This can be changed from the config file.

The SD card needs to be formatted as FAT16 or FAT32, with the Linux kernel, device tree and filesystem images placed in the root of the card.

Linux images

The Linux distribution meant to be used with tiny-rv32ima is built from buildroot-tiny-rv32ima. Pre-built images are available in the Releases section of the buildroot-tiny-rv32ima repo.

What it does

On powerup, the board waits for a keypress on the console. After that, the Linux kernel will be copied into RAM. In a few seconds, kernel messages will start streaming on the console. The boot process takes around 30 seconds.

Pictures

• VGA console:

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• Serial (USB or UART) console:

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