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 then check out nerves_system_rpi. That system configures the USB port in host mode by default and is probably more appropriate for your setup.

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Feature	Description
CPU	1 GHz ARM1176JZF-S
Memory	512 MB
Storage	MicroSD
Linux kernel	4.19 w/ Raspberry Pi patches
IEx terminal	OTG USB serial port (ttyGS0). Can be changed to HDMI or UART.
GPIO, I2C, SPI	Yes - Elixir Circuits
ADC	No
PWM	Yes, but no Elixir support
UART	1 available - ttyAMA0
Camera	Yes - via rpi-userland
Ethernet	No
WiFi	Supported on the Pi Zero W
Bluetooth	Not supported yet
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=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.

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:

cmd("espeak -ven+f5 -k5 -w /tmp/out.wav Hello")
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:

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.

Installation

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 application partition, and enabling ssh-based firmware updates.

Linux kernel configuration notes

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, and to save space. To reproduce the kernel configuration found here, do the following (this is somewhat tedious):

1. Start with arch/arm/configs/bcmrpi_defconfig. This is the kernel configuration used in the official Raspberry Pi images.
2. Turn off all filesystems except for ext4, squashfs, tmpfs, proc, sysfs, and vfat. Squashfs only needs ZLIB support.
3. vfat needs to default to utf8. Enable native language support for ascii, utf-8, ISO 8859-1, codepage 437, and codepage 850.
4. Disable all network drivers and wireless LAN drivers except for Broadcom FullMAC WLAN.
5. Disable PPP and SLIP
6. Disable the WiFi drivers in the Staging drivers menus
7. Disable TV, AM/FM, Media USB adapters, DVB Frontends and Remote controller support in the Multimedia support menus.
8. Go to Device Drivers->Sound card support. Disable USB sound devices in ALSA. Disable Open Sound System.
9. Go to Device Drivers->Graphics support. Disable DisplayLink
10. Disable everything in HID support (NOTE: revisit for Bluetooth)
11. Disable everything in input device support (can't plug it in anyway)
12. In the Device Drivers > USB support menu, enable gadget mode and disable all host mode. It should be possible to completely disable USB host mode if all of the USB drivers in previous steps were disabled. See DesignWare USB2 Core Support->DWC Mode Selection and select CDC Composite Device (Ethernet and ACM). If you want dual mode USB host/gadget support, you'll need to reenable a few things. There have been unresolved issues in the past with dual mode support. It's possible that they are fixed, but be sure to test. They were noticed on non-Mac platforms.
13. In Kernel Features, select Preemptible Kernel (Low-Latency Desktop), disable the memory allocator for compressed pages.
14. In Userspace binary formats, disable support for MISC binaries.
15. In Networking support, disable Amateur Radio support, CAN bus subsystem, IrDA subsystem, Bluetooth, WiMAX, Plan 9, and NFC. (TBD - this may be too harsh, please open issues if you're using any of these and it's the only reason for you to create a custom system.)
16. In Networking options, disable IPsec, SCTP, Asynchronous Transfer Mode, 802.1d Ethernet Bridging, L2TP, VLAN, Appletalk, 6LoWPAN, 802.15.4, DNS Resolver, B.A.T.M.A.N, Open vSwitch, MPLS, and the Packet Generator in Network testing.
17. In Networking support->Wireless, enable "use statically compiled regulatory rules database". Build in cfg80211 and mac80211. Turn off mac80211 mesh networking and LED triggers. Turn off cfg80211 wireless extensions compatibility.
18. In Kernel hacking, disable KGDB, and Magic SysRq key.
19. In Device Drivers, disable MTD support. In Block devices, disable everything but Loopback and RAM block device. Disable SCSI device support. Disable RAID and LVM.
20. In Enable the block layer, deselect everything but the PC BIOS partition type (i.e., no Mac partition support, etc.).
21. In Enable loadable module support, select "Trim unused exported kernel symbols". NOTE: If you're having trouble with an out-of-tree kernel module build, try deselecting this!!
22. In General Setup, turn off initramfs/initfd support, Kernel .config support, OProfile.
23. In Device Drivers -> I2C -> Hardware Bus Support compile the module into the kernel and disable everything but BCM2708 BSC support.
24. In Device Drivers -> SPI compile in the BCM2835 SPI controller and User mode SPI device driver support.
25. In Device Drivers -> Dallas's 1-wire support, disable everything but the GPIO 1-Wire master and the thermometer slave. (NOTE: Why is the thermometer compiled in? This seems historical.)
26. Disable Hardware Monitoring support, Sonics Silicon Backplane support
27. In Device Drivers -> Character devices -> Serial drivers, disable 8250 and SC16IS7xx support. Disable the RAW driver.
28. In Networking support->Network options, disable IP: kernel level autoconfiguration
29. In Networking support->Network options->TCP: advanced congestion control disable everything except for CUBIC TCP.
30. Disable Real Time Clock.
31. Disable everything in Cryptographic API and Library routines that can be disabled. Sometimes you need to make multiple passes.
32. Disable EEPROM 93CX6 support, PPS support, all GPIO expanders, Speakup core, Media staging drivers, STMicroelectronics STMPE, anything "Wolfson".
33. Disable most ALSA for SoC audio support and codecs. NOTE: We probably should support a few, but I have no clue which ones are most relevant and there are tons of device drivers in the list.
34. Disable IIO and UIO.
35. Disable NXP PCA9685 PWM driver

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