Base Nerves system configuration for the BeagleBone Black and Green
Shell Elixir Batchfile
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Buildroot 2016.11.1 BR2_EXTERNAL update

README.md

BeagleBone Black

Build Status

This is the base Nerves System configuration for the BeagleBone Black. It also works on the BeagleBone Green.

BeagleBone Black image
Image credit

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 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".

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:

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:

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 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.

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, 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: This image is from the Fritzing parts library.