nerves_system_bbb

# BeagleBone Black
[![Build Status](https://travis-ci.org/nerves-project/nerves_system_bbb.png?branch=master)](https://travis-ci.org/nerves-project/nerves_system_bbb)
This is the base Nerves System configuration for the [BeagleBone Black](http://beagleboard.org/black). It
also works on the [BeagleBone Green](http://beagleboard.org/green).
![BeagleBone Black image](assets/images/beaglebone-black.png)
<br><sup>[Image credit](#fritzing)</sup>
| Feature              | Description                     |
| -------------------- | ------------------------------- |
| CPU                  | 1 GHz ARM Cortex-A8             |
| Memory               | 512 MB DRAM                      |
| Storage              | 4 GB eMMC Flash and MicroSD         |
| Linux kernel         | 4.4.43 w/ BBB patches |
| IEx terminal         | ttyS0 via the FTDI connector |
| GPIO, I2C, SPI       | Yes - Elixir ALE            |
| ADC                  | Yes                             |
| PWM                  | Yes, but no Elixir support      |
| UART                 | ttyS0 + more via device tree overlay  |
| Camera               | None                            |
| Ethernet             | Yes    |
| WiFi                 | Requires USB WiFi dongle        |
## Preparing your BeagleBone
The BeagleBone hardware is configured to always try the
eMMC Flash first when looking for software. If you have a new BeagleBone,
it will boot to Debian even if a MicroSD card is inserted with good
software. To boot from the MicroSD card, hold down the USER button and
apply power.
When starting with Nerves, you will find that booting
from a MicroSD card is convenient since you can easily recover
from broken software images. Holding down the USER button will get
old. To force the BeagleBone to boot
from the MicroSD card, simply corrupt the image on the eMMC memory.
Don't worry, the BeagleBone website has instructions for restoring
Debian.
From Debian:
```
debian@beaglebone:~$ sudo dd if=/dev/zero of=/dev/mmcblk0 bs=1M count=100
100+0 records in
100+0 records out
104857600 bytes (105 MB) copied, 5.72098 s, 18.3 MB/s
debian@beaglebone:~$ sudo reboot
```
When it reboots, it will boot from the MicroSD slot. If a MicroSD card hasn't
been inserted or if there are errors reading it, you will see the letter `C` printed
repeatedly on the console port.
## Console access
The console is configured to output to `ttyS0` by default. This is the
UART output accessible by the 6 pin header labeled J1. A 3.3V FTDI
cable is needed to access the output.
The HDMI output has been disabled via device tree to free up pins on the
GPIO header. If you would like console access via HDMI, you will need
to enable HDMI support in the Linux kernel, remove the HDMI disable
argument in the uboot script providing kernel arguments, and change
`erlinit.conf` to output to `tty1`.
## Linux versions
The BeagleBone Black has many options for Linux that vary by
kernel version and patch set. Nerves tracks those maintained by
Robert Nelson at https://eewiki.net/display/linuxonarm/BeagleBone+Black.
His patch sets have `-rt` and `-ti`/`-bone` options. The `-rt` for real-time
actually refers to `CONFIG_PREEMPT` and a couple other real-time options being
configured in the Linux kernel. Nerves uses those options as well. Nerves
follows the `-ti` patch set. See `nerves_system_br/boards/bbb` for the actual
patches.
Be aware that if you have been using Linux kernel 3.8 on the BeagleBone, that there
have been device tree overlay and PRU updates. File paths have changed for
inserting device tree overlays.
## Device tree overlays
Most pins on the BBB's headers are configurable via the device tree.
Configuration can be done at runtime via the [Universal I/O](https://github.com/cdsteinkuehler/beaglebone-universal-io)
device tree overlays. These overlays are included in the kernel configuration
for Nerves so you do not need to compile that project. Additionally, the
`config-pin` script is available in `/usr/bin` on the target. It has
minor modifications to run on Nerves.
### Universal I/O
The universal I/O overlays can be loaded manually or by using the `config-pin`
shell script:
```
iex(demo@nerves-0099)> :os.cmd('config-pin overlay cape-universaln')
'Loading cape-universaln overlay\n'
iex(demo@nerves-0099)> :os.cmd('config-pin -i P9_16') |> IO.puts
Pin name: P9_16
Function if no cape loaded: gpio
Function if cape loaded: default gpio gpio_pu gpio_pd pwm
Function information: gpio1_19 default gpio1_19 gpio1_19 gpio1_19 ehrpwm1B
Cape: cape-universala cape-universal cape-universaln
Kernel GPIO id: 51
PRU GPIO id: 83
:ok
iex(demo@nerves-0099)> :os.cmd('config-pin P9_16 pwm')
```
### ADCs
The following example shows how to read values from the 7 ADC inputs in Elixir.
```
iex(demo@nerves-0099)> File.write("/sys/devices/platform/bone_capemgr/slots","BB-ADC")
:ok
iex(demo@nerves-0099)> ls "/sys/bus/iio/devices/iio:device0"
buffer              dev                 in_voltage0_raw     in_voltage1_raw
in_voltage2_raw     in_voltage3_raw     in_voltage4_raw     in_voltage5_raw
in_voltage6_raw     name                of_node             power
scan_elements       subsystem           uevent
iex(demo@nerves-0099)> File.read("/sys/bus/iio/devices/iio:device0/in_voltage0_raw")
{:ok, "3891\n"}
iex(demo@nerves-0099)> File.read("/sys/bus/iio/devices/iio:device0/in_voltage0_raw")
{:ok, "3890\n"}
iex(demo@nerves-0099)> File.read("/sys/bus/iio/devices/iio:device0/in_voltage0_raw")
{:ok, "3891\n"}
```
### SPI
The following examples shows how to get SPI0 functional in Elixir.
Load the overlay, configure the pins, and load the device drivers:
> Note: The order of the above stops is important. The overlay must be loaded and the pins configured before writing "BB-SPIDEV0".
```console
iex(demo@nerves-0099)1> :os.cmd('config-pin overlay cape-universaln')
'Loading cape-universaln overlay\n'
iex(demo@nerves-0099)2> [17,18,21,22] |> Enum.each(&(:os.cmd('config-pin -a  P9_#{&1} spi')))
:ok
iex(demo@nerves-0099)3> File.write("/sys/devices/platform/bone_capemgr/slots","BB-SPIDEV0")
{:error, :eexist}
```
Verify that the device drivers are loaded and read spi0 transfers:
```console
iex(demo@nerves-0099)4> ls "/dev"
  ...
        spidev1.0              spidev1.1              spidev2.0              spidev2.1
  ...
iex(demo@nerves-0099)5> File.read "/sys/bus/spi/devices/spi1.0/statistics/transfers"
{:ok, "0"}
```
Verify that the pins are configured:
```console
iex(demo@nerves-0099)6> [17,18,21,22] |> Enum.map(&(:os.cmd('config-pin -q  P9_#{&1} spi')))
['P9_17 Mode: spi\n', 'P9_18 Mode: spi\n', 'P9_21 Mode: spi\n', 'P9_22 Mode: spi\n']
```
If you have included [ElixirAle](https://github.com/fhunleth/elixir_ale) as a dependency, you can start it now and test a transfer:
> The example below should work without any additional hardware connected to the BBB. If you have SPI hardware connected to the BBB, your returned binary might be different.
```console
iex(demo@nerves-0099)7> Spi.start_link "spidev1.0", [], name: :spi0
{:ok, #PID<0.181.0>}
iex(demo@nerves-0099)8> Spi.transfer :spi0, <<1,2,3,4>>
<<255, 255, 255, 255>>
```
> Note: If you get back all 0's, then you have likely have not configured the overlay pins correctly.
## Supported USB WiFi devices
The base image includes drivers and firmware for Ralink RT53xx
(`rt2800usb` driver) and RealTek RTL8712U (`r8712u` driver) devices.
We are still working out which subset of all possible WiFi dongles to
support in our images. At some point, we may have the option to support
all dongles and selectively install modules at packaging time, but until
then, these drivers and their associated firmware blobs add significantly
to Nerves release images.
If you are unsure what driver your WiFi dongle requires, run Raspbian and configure WiFi
for your device. At a shell prompt, run `lsmod` to see which drivers are loaded.
Running `dmesg` may also give a clue. When using `dmesg`, reinsert the USB
dongle to generate new log messages if you don't see them.
## Installation
If [available in Hex](https://hex.pm/docs/publish), the package can be installed as:
  1. Add nerves_system_bbb to your list of dependencies in `mix.exs`:
        def deps do
          [{:nerves_system_bbb, "~> 0.10.0"}]
        end
  2. Ensure nerves_system_bbb is started before your application:
        def application do
          [applications: [:nerves_system_bbb]]
        end
[Image credit](#fritzing): This image is from the [Fritzing](http://fritzing.org/home/) parts library.