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https://github.com/farmbot/farmbot_system_rpi3


https://github.com/farmbot/farmbot_system_rpi3

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README 

        
# Raspberry Pi 3 Model B / B+



[![CircleCI](https://circleci.com/gh/FarmBot-Labs/farmbot_system_rpi3.svg?style=svg)](https://circleci.com/gh/FarmBot-Labs/farmbot_system_rpi3)

[![Hex version](https://img.shields.io/hexpm/v/farmbot_system_rpi3.svg "Hex version")](https://hex.pm/packages/farmbot_system_rpi3)



This is the base Nerves System configuration for the Raspberry Pi 3 Model B.



![Fritzing Raspberry Pi 3 image](assets/images/raspberry-pi-3-model-b.png)


[Image credit](#fritzing)



| Feature              | Description                                                 |

| -------------------- | ----------------------------------------------------------- |

| CPU                  | 1.2 GHz quad-core Cortex-A53 (ARMv8)                        |

| Memory               | 1 GB DRAM                                                   |

| Storage              | MicroSD                                                     |

| Linux kernel         | 6.1 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                                                         |

| Bluetooth            | [See Bluetooth](#bluetooth)                                 |

| 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/customizing-systems.html).



## Supported WiFi devices



The base image includes drivers for the onboard Raspberry Pi 3 wifi module

(`brcmfmac` driver).



## Bluetooth



[BlueHeronTransportUART](https://github.com/blue-heron/blue_heron_transport_uart)

supports bluetooth on the Pi 3A using `ttyS0`. The details are similar to the [RPi Zero W]

(https://github.com/nerves-project/nerves_system_rpi0/issues/224#issuecomment-913799838).



## 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.



The general Raspberry Pi audio documentation mostly applies to Nerves. For

example, to force audio out the HDMI port, run:



```elixir

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.