# Raspberry Pi 3 Model B / B+
[](https://circleci.com/gh/nerves-project/nerves_system_rpi3)
[](https://hex.pm/packages/nerves_system_rpi3)
This is the base Nerves System configuration for the Raspberry Pi 3 Model B.
<br><sup>[Image credit](#fritzing)</sup>
| Feature | Description |
| -------------------- | ----------------------------------------------------------- |
| CPU | 1.2 GHz quad-core Cortex-A53 (ARMv8) |
| Memory | 1 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](https://github.com/elixir-circuits) |
| ADC | No |
| PWM | Yes, but no Elixir support |
| UART | 1 available - `ttyAMA0` |
| Display | HDMI or 7" RPi Touchscreen |
| Camera | Yes - via rpi-userland |
| Ethernet | Yes |
| WiFi | Yes - Nerves.Network |
| Bluetooth | Watch [Harald](https://github.com/verypossible/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=rpi3`. See the [Getting started
guide](https://hexdocs.pm/nerves/getting-started.html#creating-a-new-nerves-app)
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](https://hexdocs.pm/nerves/systems.html#customizing-your-own-nerves-system)
## Supported WiFi devices
The base image includes drivers for the onboard Raspberry Pi 3 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:
```elixir
: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:
```elixir
:os.cmd('amixer cset numid=3 2')
```
Change the last argument to `amixer` to `1` to output to the stereo output jack.
## Linux's preempt_rt patches
If you need better real-time performance from the Linux kernel, the `preempt_rt`
patch set may help. Be aware that we do not test with the patches so this may
not work. To enable it, make a custom system using this one as a base and add
the following to the `nerves_defconfig`:
```text
BR2_LINUX_KERNEL_PATCH="http://cdn.kernel.org/pub/linux/kernel/projects/rt/4.19/patch-4.19.25-rt16.patch.xz"
```
Please verify the patch version since these instructions may be out-of-date.
Next, update the Linux configuration to use it. Review the Nerves documentation
for running `make linux-menuconfig` and enable `PREEMPT_RT_FULL`. Alternately,
make the following change to the Linux configuration:
```text
-CONFIG_PREEMPT=y
+CONFIG_PREEMPT_RT_FULL=y
```
Build the system and you should now have a preempt_rt kernel.
## 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`](https://hexdocs.pm/nerves_runtime/Nerves.Runtime.KV.html#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:
```elixir
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:
```sh
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, 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.
1. Turn off all filesystems except for `ext4`, `squashfs`, `tmpfs`, `proc`,
`sysfs`, and `vfat`. Squashfs only needs ZLIB support.
1. `vfat` needs to default to `utf8`. Enable native language support for
`ascii`, `utf-8`, `ISO 8859-1`, codepage 437, and codepage 850.
1. Disable all network drivers and wireless LAN drivers except for Broadcom
FullMAC WLAN.
1. Disable PPP and SLIP
1. Disable the WiFi drivers in the Staging drivers menus
1. Disable TV, AM/FM, Media USB adapters, DVB Frontends and Remote controller
support in the Multimedia support menus.
1. Go to `Device Drivers->Sound card support`. Disable `USB sound devices` in
ALSA. Disable `Open Sound System`.
1. Go to `Device Drivers->Graphics support`. Disable `DisplayLink`
1. In `Kernel Features`, select `Preemptible Kernel (Low-Latency Desktop)`,
disable the memory allocator for compressed pages.
1. In `Userspace binary formats`, disable support for MISC binaries.
1. 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.)
1. 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.
1. 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.
1. In `Kernel hacking`, disable KGDB, and Magic SysRq key.
1. In Device Drivers, disable MTD support. In Block devices, disable everything
but Loopback and RAM block device. Disable RAID and LVM.
1. In `Enable the block layer`, deselect everything but the PC BIOS partition
type (i.e., no Mac partition support, etc.).
1. 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 deslecting this!!
1. In `General Setup`, turn off `initramfs/initfd` support, Kernel .config
support, OProfile.
1. In `Device Drivers -> I2C -> Hardware Bus Support` compile the module into
the kernel and disable everything but `BCM2708 BSC` support.
1. In `Device Drivers -> SPI` compile in the BCM2835 SPI controller and User
mode SPI device driver support.
1. In `Device Drivers -> Staging` disable `Support for small TFT LCD modules`
1. 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.)
1. Disable `Hardware Monitoring support`, `Sonics Silicon Backplane support`
1. In `Device Drivers -> Character devices -> Serial drivers`, disable 8250 and
SC16IS7xx support. Disable the RAW driver.
1. In `Networking support->Network options`, disable `IP: kernel level
autoconfiguration`
1. In `Networking support->Network options->TCP: advanced congestion control`
disable everything except for `CUBIC TCP`.
1. Disable `Real Time Clock`.
1. Disable everything in `Cryptographic API` and `Library routines` that can be
disabled. Sometimes you need to make multiple passes.
1. Disable EEPROM 93CX6 support, PPS support, all GPIO expanders, Speakup core,
Media staging drivers, STMicroelectronics STMPE, anything "Wolfson".
1. 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.
1. Disable IIO and UIO.
1. Disable NXP PCA9685 PWM driver
[Image credit](#fritzing): This image is from the [Fritzing](http://fritzing.org/home/) parts library.
