Base Nerves system configuration for the Lego EV3
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README.md

Lego Mindstorms EV3

CircleCI Hex version

This is the base Nerves System configuration for the Lego Mindstorms EV3 brick.

EV3 brick image
Image credit

Feature Description
CPU 300 MHz ARM926EJ-S
Memory 64 MB DRAM
Storage 16 MB Flash and MicroSD
Linux kernel 4.4 w/ ev3dev patches
Display 178x128 LCD - /dev/fb0
IEx terminal USB Gadget port or port 1 (see below)
GPIO, I2C, SPI Yes - ev3dev drivers
ADC Yes
PWM Yes, but no Elixir support
UART 4 available - ttyACM0
Speakers Built-in speaker - ALSA
Camera None
Ethernet Requires USB Ethernet dongle
WiFi Requires USB WiFi dongle
Bluetooth Not supported

Using

The most common way of using this Nerves System is create a project with mix nerves.new and to export MIX_TARGET=ev3. See the Getting started guide for more information.

If you need custom modifications to this system for your device, clone this repository and update as described in Making custom systems

I recommend creating a project that uses nerves_init_gadget to get started on the EV3. This makes using the EV3 similar to the Raspberry Pi Zero so more help will be available on the Nerves slack channel and forum.

Ethernet for uploading new firmware images is provided through the USB gadget port (labelled "PC" on the EV3). If you connect this via a USB cable to your laptop and turn on the EV3, you should eventually see a new USB and Ethernet port. (The first boot of Nerves on the EV3 takes some time.)

Unfortunately, the console doesn't appear to work via the Gadget USB port. I haven't had time to debug this, so I left it going through ttyS1 which comes out port 1. This is very sad. If you have a clue on how to fix this, see rootfs_overlay/etc/erlinit.config to route the console through ttyGS0 and let me know.

The Lego device kernel modules are not built into the kernel so they need to be loaded by your application at initialization time. To do this, run the following manually or add them to your application:

iex> :os.cmd('modprobe suart_emu')
iex> :os.cmd('modprobe legoev3_ports')
iex> :os.cmd('modprobe snd_legoev3')
iex> :os.cmd('modprobe legoev3_battery')

When Nerves supports Bluetooth, you'll want to run the following line as well:

iex> :os.cmd('modprobe legoev3_bluetooth')

Once you get to the console and can update firmware, you should be able to follow ev3dev instructions for reading and writing to files to control motors, read sensors, and everything else that the EV3 can do.

Example projects

Since the documentation is sparse here, you may find some example projects helpful:

If you have a project to share, please help us by adding it to the list and sending a pull request. Thanks!

Port 1 console access

The EV3 supports a special UART output on port 1. Nerves can use this output for Linux kernel debug messages and an IEx prompt. If you plan on doing any Linux kernel, driver, or boot related work with the EV3, this console is indispensable.

You will either need to buy a console adapter or build one to use this port.

Loading the legoev3_ports driver automatically disables the console port. Since we're working on the EV3 and it's not as easy to use as it should be, we've told the legoev3_ports module to not touch it. If you're on the EV3, you'll see the following line in /etc/modprobe.d/ev3dev.conf:

options legoev3_ports disable_in_port=1

If you want to use port 1, you'll need to disable this. To do this, add a /etc/modprobe.d/ev3dev.conf to your project's rootfs_overlay. If an empty file exists, it will override this default one, but I usually create a file with the line commented out so that I remember what the special line is.

Supported USB WiFi devices

The base image includes drivers and firmware for Ralink RT53xx (rt2800usb driver), MediaTek MT7601U (mt7601u), and Edimax EW-7811Un (8192cu) devices. One option for these devices is to get a Tenda W311MI Wireless USB Adapter.

We are still working out which subset of all possible WiFi dongles to support in our images. At some point, we may have the option to support all dongles and selectively install modules at packaging time, but until then, these drivers and their associated firmware blobs add significantly to Nerves release images.

If you are unsure what driver your WiFi dongle requires, run Raspbian and configure WiFi for your device. At a shell prompt, run lsmod to see which drivers are loaded. Running dmesg may also give a clue. When using dmesg, reinsert the USB dongle to generate new log messages if you don't see them.

Wired Ethernet

If you have a USB Ethernet adapter, find the driver for it on your PC. For example, plug it in and check dmesg and lsmod to see which driver it loads. In my case, I have an adapter that loads the asix driver. Make sure that your driver is compiled in as a module to the Linux kernel in Nerves and then manually load the driver via modprobe asix.

Power down, halt, reboot

On most platforms, the default behavior of Nerves is to hang if something goes wrong. This is good for debugging since rebooting makes it easy to lose console messages or it might hide the issue completely. On the EV3 hanging requires a slightly more complex restarting process.

  1. Hold down the Back, and center buttons on the EV3 Brick
  2. When the screen goes blank, release the Back button
  3. When the screen says “Starting,” release the center button

If you would like to power down instead you will need to change erlinit.config from --hang-on-exit to ---poweroff-on-exit.

If you're attached to the console, you may see a kernel panic when you run power off. From what I can tell, this panic happens after the important parts of shutting down gracefully have completed and does not cause a problem.

SDCard vs. internal NAND Flash notes

The EV3 brick has a 16 MB NAND Flash inside it that's connected to SPI bus 0. It doesn't look like the ev3dev project has included support for it yet except in their version of u-boot. The means that it can only be programmed using the Lego supplied tools. The 16 MB NAND Flash also has a couple other issues. First, it appears to be super slow. This leads to them copying the whole image to DRAM instead of reading it as needed. It appears that this uses up 10 MB of DRAM compared to running off the SDCard. This is significant when you consider that the board only has 64 MB total DRAM. On the other hand, programming the internal NAND Flash is cool and the direction that we'd prefer to go on production systems.

Currently, the u-boot in the internal NAND Flash that's supplied by Lego and the ev3dev project expects the uImage in the first VFAT partition. Ideally, it would extract it out of the rootfs so that we could implement more atomic firmware updates. To avoid the need to reflash the firmware to use Nerves, I'm staying with the existing mechanism.

ev3dev

This port draws substantially on the ev3dev project. In general, if there's a way to do something in ev3dev, it can be made to work in Nerves. Nerves uses the same Linux kernel from the ev3dev project and enables the same set of custom drivers that were created by the ev3dev developers.

Provisioning devices

This system supports storing provisioning information in a small key-value store outside of any filesystem. Provisioning is an optional step and reasonable defaults are provided if this is missing.

Provisioning information can be queried using the Nerves.Runtime KV store's Nerves.Runtime.KV.get/1 function.

Keys used by this system are:

Key Example Value Description
nerves_serial_number "1234578"` By default, this string is used to create unique hostnames and Erlang node names. If unset, it defaults to part of the EV3's device ID.

The normal procedure would be to set these keys once in manufacturing or before deployment and then leave them alone.

For example, to provision a serial number on a running device, run the following and reboot:

iex> cmd("fw_setenv nerves_serial_number 1234")

This system supports setting the serial number offline. To do this, set the NERVES_SERIAL_NUMBER environment variable when burning the firmware. If you're programming MicroSD cards using fwup, the commandline is:

sudo NERVES_SERIAL_NUMBER=1234 fwup path_to_firmware.fw

Serial numbers are stored on the MicroSD card so if the MicroSD card is replaced, the serial number will need to be reprogrammed. The numbers are stored in a U-boot environment block. This is a special region that is separate from the application partition so reformatting the application partition will not lose the serial number or any other data stored in this block.

Additional key value pairs can be provisioned by overriding the default provisioning.conf file location by setting the environment variable NERVES_PROVISIONING=/path/to/provisioning.conf. The default provisioning.conf will set the nerves_serial_number, if you override the location to this file, you will be responsible for setting this yourself.

Image credit: By Klaus-Dieter Keller - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=29156877