florianb / kiosk_system_rpi4

Nerves QT5WebEngineKiosk Raspberry Pi 4 system

Raspberry Pi 4 Model B

This is the base Nerves System configuration for the Raspberry Pi 4 Model B.

^{Michael Henzler / Wikimedia Commons / CC BY-SA 4.0}

Feature	Description
CPU	1.5 GHz quad-core Cortex-A72 (ARM v8)
Memory	1 GB, 2 GB, 4 GB DRAM
Storage	MicroSD
Linux kernel	4.19 w/ Raspberry Pi patches
IEx terminal	HDMI and USB keyboard (can be changed to UART)
GPIO, I2C, SPI	Yes - Elixir Circuits
ADC	No
PWM	Yes, but no Elixir support
UART	1 available - ttyS0
Display	HDMI or 7" RPi Touchscreen
Camera	Yes - via rpi-userland
Ethernet	Yes
WiFi	Yes - Nerves.Network
Bluetooth	Watch Harald
Audio	HDMI/Stereo out

Using

The most common way of using this Nerves System is create a project with mix nerves.new and to export MIX_TARGET=rpi4. 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. It will get you started with the basics like bringing up networking, initializing the writable application data partition, and enabling ssh-based firmware updates. It's easiest to begin by using the wired Ethernet interface 'eth0' and DHCP.

Supported WiFi devices

The base image includes drivers for the onboard Raspberry Pi 4 wifi module (brcmfmac driver).

Audio

The Raspberry Pi has many options for audio output. This system supports the HDMI and stereo audio jack output. The Linux ALSA drivers are used for audio output.

To try it out, run:

:os.cmd('espeak -ven+f5 -k5 -w /tmp/out.wav Hello')
:os.cmd('aplay -q /tmp/out.wav')

The general Raspberry Pi audio documentation mostly applies to Nerves. For example, to force audio out the HDMI port, run:

:os.cmd('amixer cset numid=3 2')

Change the last argument to amixer to 1 to output to the stereo output jack.

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	"12345678"	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 nerves_serial_number 12345678")

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=12345678 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.

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.

Linux kernel configuration

The Linux kernel compiled for Nerves is a stripped down version of the default Raspberry Pi Linux kernel. This is done to remove unnecessary features, select some Nerves-specific features like F2FS and SquashFS support, and to save space.