Raspberry Pi Pico 2 Buildroot

How to build:

# Prepare Repo
git clone https://github.com/Mr-Bossman/pi-pico2-linux
cd pi-pico2-linux
git submodule update --init

# Build Linux Image
make -C buildroot BR2_EXTERNAL="$PWD/" raspberrypi-pico2_defconfig
make -C buildroot

# Build 2nd Stage Bootloader, and flash it and the kernel
# (See notes on Toolchain and SDK below for ENV setup)
make -C psram-bootloader flash-kernel

Designed to work with SparkFun Pro Micro - RP2350

Also working on the Pimoroni Pico 2 Plus

NOTES on Toolchain

The Pico SDK Manual section 2.10 suggests installing and using the "Top of Tree" Corev Compiler Toolchain.

# Install the Corev Toolchain to /opt/riscv/corev-openhw-gcc-*/
sudo mkdir -p /opt/riscv/
cd /opt/riscv/
sudo tar -xvf /path/to/corev-openhw-gcc*.tar.gz

To use this toolchain with the Pico SDK, set the PICO_TOOLCHAIN_PATH variable.

export PICO_TOOLCHAIN_PATH="$(realpath /opt/riscv/corev-openhw-gcc-*)"

NOTES on SDK

The Pico SDK is expected to be downloaded at ~/.pico-sdk/. To use the SDK and Tools installed to another location see this issue.

In short, PICO_SDK_PATH must be set to the path of your SDK install.

export PICO_SDK_PATH="~/example_sdk/sdk/2.0.0/"

# The SDK should assume these. They weren't necessary for me. 
# export pioasm_DIR=~/example_sdk/tools/2.0.0/pioasm
# export picotool_DIR=~/example_sdk/picotool/2.0.0/picotool

NOTES on Picotool

Picotool is required to load the Linux image onto the SPI flash.

picotool can be built without this image loading support. This happens if cmake can not find libusb 1.0 at buildtime. When this occurs, the help message of picotool will read as follows:

Tool for interacting with an RP2040/RP2350 binary

When image loading support has been built successfully, the help message will mention interacting with boards in BOOTSEL mode:

Tool for interacting with RP2040/RP2350 device(s) in BOOTSEL mode, or with an RP2040/RP2350 binary

Suggest manually building picotool if having issues with it missing libusb. It is available on github.

NOTES on Atomics

On page 307 of the RP2350 Datasheet MCAUSE register CODE 7 says:

Store/AMO access fault. A store/AMO failed a PMP check, or encountered a downstream bus error. Also set if an AMO is attempted on a region that does not support atomics (on RP2350, anything but SRAM).

Atomics will only work in SRAM, the kernel is located PSRAM, not SRAM. The lr and sr atomic load and store will always return error in this region causing most code using them to behave incorrectly. Most implementations assume lr and sr will eventually succeed.

Use on other boards

This only works on the RP2350 RISC-V cores.

If you want to run this on other boards, please change the PICO_BOARD variable in CMakeLists.txt. set(PICO_BOARD sparkfun_promicro_rp2350 CACHE STRING "Board type")

You will also need to set the psram CS pin with the SFE_RP2350_XIP_CSI_PIN macro in bootloader.c. As of now the only psram chip tested is the APS6404L and any others may not work.