About

HIGHLY WORK-IN-PROGRESS, CODE NOT COMPLETELY WORKING YET AND MAY NOT BUILD.

Lego Mindstorms NXT2 (ARM7-TDMI, AT91SAM7S, 64 kB RAM, bare-metal) C/C++ FW communicating with Raspberry Pi Zero 2 W (ARM Cortex-A53, 512 MB RAM, Cortex-A53, Debian Linux 10/11) C++/Python SW.

Unfortunately I only have Lego NXT2s and don't want to buy a new EV3 set (the NXT2 was phased out several years ago). However, ARM low-level programming is more fun for me. So I experiment with own bare-metal firmware on the NXT (for sensor/actuator servicing) and control software on the Raspberry Pi (for the algorithms).

Long-term goal: Raspberry Pi4 (or: Pi 3, Pi Zero 2 W) solving a Rubik's cube via Python/OpenCV and then controlling the NXT to physically solve it.

Credits

The FW is partly inspired by the LeJos project (especially the AVR support code and the I2C driver code initially based on the code from there).

TODO License?

Prerequisites

I'm using Ubuntu 20 as development platform and a RasPi Zero 2 W (or RasPi 3B) as the computer controlling the NXT2.

The embedded cross-build environment can be caught via Docker image below.

Build requirements (e.g. on Ubuntu 20)

Install host build environment

sudo apt install git cmake gcc g++ gdb-multiarch

Install required libraries

sudo apt install python3-dev
sudo apt install python3-pybind11
sudo apt install libncurses5-dev
sudo apt install libusb-1.0-0-dev

Runtime requirements (e.g. on Raspberry OS)

Install required libraries

sudo apt install python3
sudo apt install libusb-1.0-0

Build

Docker for Cross-Building

Install Docker

Run install:

sudo apt install docker.io

Setup privileges for socket:

sudo usermod -aG docker $USER

Build Image

Run setup script:

cd docker/nxt-build
./setup.sh

Run Image

Run the container:

docker run --name rpi-nxt2 -it -v <root>/rpi-nxt2:/home/rpi-nxt2 ubuntu20-gcc-arm-none-eabi:latest

To re-run after exit:

docker start rpi-nxt2 -i

Build ARM7-TDMI Firmware

Run (in container):

cd /home/rpi-nxt2
scripts/build_nxt.sh <build_type> <app_name>

Build Linux Software

Run:

cd /home/rpi-nxt2
scripts/build_linux.sh <build_type>

Flashing

Flashing the NXT FW

Install Atmel SAM-BA

SAM-BA is a flash programmer formerly developed by Atmel (from where the AT91S silicon was originally coming).

The SAM-BA flash programmer can be downloaded from MICROCHIP: https://www.microchip.com/en-us/development-tool/SAM-BA-IN-SYSTEM-PROGRAMMER#

Unpack it and set a soft-link for sam-ba_64:

sudo ln -s /opt/atmel/sam-ba/sam-ba_64 /usr/local/bin/sam-ba

Run Flash Tool

Bring the NXT into flash mode and connect it to USB or JTAG, then:

ice/sam-ba.sh

Running

Starting the NXT

To start the NXT, just insert the batteries, and it will boot. You should see the title according to your selected application (see <app_name> above).

Starting the Linux SW

USB Connection Console

There is only the USB connection monitoring console tool available yet:

build/linux/nxt_console/nxt_console

You need to apply the USB permissions rules in the config/udev/rules.d directory to get it running.

Debugging

For debugging on the NXT I use the SEGGER J-Link ICE (EDU version). For that I soldered pins of the NXT board to expose the JTAG interface. Via adapter, I then connect the ICE to the NXT.

Debugging the NXT FW

Install J-Link

The Debian package can be downloaded from SEGGER: https://www.segger.com/downloads/jlink.

Set soft-link for JLinkGDBServerCLExe:

sudo ln -s /opt/segger/jlink/JLinkGDBServerCLExe /usr/local/bin/jlink-gdbserver

Run GDB Server

Connect the JTAG connector to the J-Link ICE and run:

tools/jlink_gdbserver.sh

Attach to GDB Server

This is tools specific. I use CLion which controls the GDB. Use the host-stools GDB script tools/gdb/host_init.gdb.

Debugging the Linux SW

This is a trivial process and well-documented for your tools.

Examples

Linux Examples

Python API Demo

See linux/examples/python/hello_world.

Minimal NXT Remote Console

See linux/examples/python/nxt_console.

Cube Solver

See linux/examples/python/cube_solver.