alde103 / costum_rpi0

a custom nerves system for rpi0

Raspberry Pi Model Zero

This is the base Nerves System configuration for the Raspberry Pi Zero and Raspberry Pi Zero W.

If you are not interested in Gadget Mode it might be worth checking out nerves_system_rpi. That image configures the USB port in host mode by default and is probably more appropriate for your setup.

^{Image credit}

Feature	Description
CPU	1 GHz ARM1176JZF-S
Memory	512 MB
Storage	MicroSD
Linux kernel	4.4 w/ Raspberry Pi patches
IEx terminal	OTG USB serial port (ttyGS0). Can be changed to HDMI or UART.
GPIO, I2C, SPI	Yes - Elixir ALE
ADC	No
PWM	Yes, but no Elixir support
UART	1 available - ttyAMA0
Camera	Yes - via rpi-userland
Ethernet	Yes - via OTG USB port
WiFi	Supported on the Pi Zero W
Bluetooth	Not supported yet

Using

The most common way of using this Nerves System is create a project with mix nerves.new and to export MIX_TARGET=rpi0. 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

If you're new to Nerves, check out the nerves_init_gadget project for creating a starter project for the Raspberry Pi Zero or Zero W. It will get you started with the basics like bringing up the virtual Ethernet interface, initializing the writable application data partition, and enabling ssh-based firmware updates.

Console and kernel message configuration

The goal of this image is to use the OTG port for console access. If you're debugging the boot process, you'll want to use the Raspberry Pi's UART pins on the GPIO connector or the HDMI output. This is enabled by updating the cmdline.txt file. This may be overridden with a custom fwup.conf file if you don't want to rebuild this system. Add the following to your cmdline.txt:

console=ttyAMA0,115200 console=tty1 ...

If you'd like the IEx prompt to come out the UART pins (ttyAMA0) or HDMI (tty1), then modify rootfs_overlay/etc/erlinit.config as well.

Supported OTG USB modes

The base image activates the dwc2 overlay, which allows the Pi Zero to appear as a device (aka gadget mode). When plugged into a host computer via the OTG port, the Pi Zero will appear as a composite Ethernet and serial device. The virtual serial port provides access to the IEx prompt and the Ethernet device can be used for firmware updates, Erlang distribution, and anything else running over IP.

Supported WiFi devices

The base image includes drivers for the onboard Raspberry Pi Zero W wifi module (brcmfmac driver). Due to the USB port being placed in gadget mode, this system does not support USB WiFi adapters.

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
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 Raspberry Pi'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 serial_number 1234")

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

sudo 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.

Linux kernel and RPi firmware/userland

There's a subtle coupling between the nerves_system_br version and the Linux kernel version used here. nerves_system_br provides the versions of rpi-userland and rpi-firmware that get installed. I prefer to match them to the Linux kernel to avoid any issues. Unfortunately, none of these are tagged by the Raspberry Pi Foundation so I either attempt to match what's in Raspbian or take versions of the repositories that have similar commit times.

Image credit: This image is from the Fritzing parts library.