BeagleBone Black

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Find below my experiences with the BeagleBone Black (BBB) revision 3.

At BBB First Boot you can read about the first boot of the BeagleBone Black

Adding a WiFi adapter BBB WiFi

Yocto Project

Enabling the DS18B20 thermometer

The version of Debian that my board was supplied with uses the Flattened Device Tree in order to ease the access to GPIO's and other hardware. This are so for the most modern Linux distributions for the ARM processors. The reason for this is mainly because Linus Thorvalds did not want to include the large amount of device drivers for the ARM processor family in the kernel. Se more about the Flattened Device Tree (FDT) on this site.

From this site I was inspired to set-up the correct dts file enabling the usage of GPIO pin 2 for the 1Wire interface.

Create a file name DS1820-00A0.dts with this content

/dts-v1/;
/plugin/;
 
/ {
    compatible = "ti,beaglebone", "ti,beaglebone-black";
    part-number = "DS1820";
    version = "00A0";
 
    exclusive-use = "P9.12";
 
    fragment@0 {
        target = <&am33xx_pinmux>;
        __overlay__ {
             ds1820_pins: pinmux_ds1820_pins {
                 pinctrl-single,pins =  <0x78 0x37>;
             };
        };
    };
 
    fragment@1 {
        target = <&ocp>;
        __overlay__ {
            onewire@0 {
                status          = "okay";
                compatible      = "w1-gpio";
                pinctrl-names   = "default";
                pinctrl-0       = <&ds1820_pins>;
                gpios           = <&gpio2 28 0>;
            };
        };
    };
};

Compile the specification into a dtbo binary file

dtc -O dtb -o /lib/firmware/DS1820-00A0.dtbo -b 0 -@ DS1820-00A0.dts

Finally in order to enable this part of the device tree perform at every boot this command

echo DS1820 > /sys/devices/bone_capemgr.*/slots

The thermometer should now show up in the /sys/bus/w1/devices folder

drwxr-xr-x 2 root root 0 Jan  1  2000 .
drwxr-xr-x 4 root root 0 Jan  1  2000 ..
lrwxrwxrwx 1 root root 0 Feb 21 10:49 28-000005a7ce64 -> ../../../devices/w1_bus_master1/28-000005a7ce64
lrwxrwxrwx 1 root root 0 Feb 21 10:49 w1_bus_master1 -> ../../../devices/w1_bus_master1

the 28-00000nnnnnnn is the thermometer - they are all uniquely identified, so the n's will vary.

Test with Python

To check that the thermometer work correct prepare this short test program in a file named test.py where you of course will adjust the thermometer ID to suit your set-up:

import time
 
w1="/sys/bus/w1/devices/28-000005a7ce64/w1_slave"
 
while True:
    raw = open(w1, "r").read()
    print "Temperature is "+str(float(raw.split("t=")[-1])/1000)+" degrees"
    time.sleep(1)

Execute the program

python test.py

you should get something similar to this

root@klaus-BBB:~/ds18b20# python test.py 
Temperature is 24.0 degrees
Temperature is 24.0 degrees
Temperature is 24.062 degrees
Temperature is 24.062 degrees
^CTraceback (most recent call last):
  File "test.py", line 8, in <module>
    time.sleep(1)
KeyboardInterrupt
root@klaus-BBB:~/ds18b20#

Test using Bonescript

This source first locates the attached thermometer and then uses it for temperature reading.

This code is only able to handle one thermometer at a time, or in fact only one 1-wire device at at time.

// 
// Interface for the thermometer
// Author   : Klaus Kolle
// Date     : 2015 02 22
// Revision : 0.0.3
 
var b = require('bonescript');
var f = require('fs');
 
//console.log('Hello, Thermostate.');
 
var temperature;
 
// Read from the 1-wire thermometer
// The 28-00000nnnnnnn will change depending of the device connected
// 
var oneWireDir;
 
locateThermometer();
 
function locateThermometer()
{
  var initialDir = '/sys/bus/w1/devices/';
  var regExpr = '28-00000';
  var dir = [];
  var i;
  // Get all files and directories in the dir
  var dirs = f.readdirSync(initialDir);
  // Did we gat anything - if not the cape manager is probably not initialised
  // with the dtbo compiled device tree
  if (dirs.length > 0)
  {
    for (i = 0; i < dirs.length; i++)
    {
      // Only select the directories matching the pattern
      if(dirs[i].match(regExpr))
      {
        dir.push (dirs[i]);
      }
    }
    // Currently the code only accepts one thermometer
    oneWireDir = initialDir + dir + "/w1_slave";
  }
}
 
function readTemp() 
{
  // Callback function for the timer
  b.readTextFile(oneWireDir, printTemp);
}
 
// The 1-wire returs this when reading the device
// klaus@klaus-BBB:~$ cat /sys/bus/w1/devices/28-000005a7ce64/w1_slave 
// a5 01 4b 46 7f ff 0b 10 f7 : crc=f7 YES
// a5 01 4b 46 7f ff 0b 10 f7 t=26312
// Therefore a split is needed. We need the string after the second =
 
function printTemp(x) 
{
  // We receive the data i x
  if (x.data != '')
  {
    var stringToSplit = x.data;
    // Split at = - three resulting strings are returned
    var arrayOfStrings = stringToSplit.split('=');
    // We are only interesd in the last
    temperature = (arrayOfStrings[2]) / 1000;
    console.log("Temp: " + temperature);
  }
}
 
setInterval(readTemp, 5000);

Expect a readout like this

Temp: 24.687
Temp: 24.75
Temp: 24.75
Temp: 24.687
Temp: 24.75
Temp: 24.75
Temp: 24.75
Temp: 24.687

Development on a PC host and remote debugging

A few things are needed in order to set-up development of programs, that shall execute on an ARM platform. You'll need a cross compiler - a compiler that can generate ARM executable code while the compiler is executed on the PC platform, which is typically a Intel X86_64 architecture.

Cross Compiler

The Fedora package system does not contain a suitable compiler for the ARMv7 processor.

Luckily Linaro, does maintain a toolchain suitable for us. At this point you can find the newest binaries for your operating system. Go up the directory structure to discover if a newer compiler has been released.

The following is suited for Fedora Linux and other Linux'es as they are rather generic.

]$ cd ~/Downloads
$] wget http://releases.linaro.org/14.11/components/toolchain/binaries/arm-linux-gnueabihf/gcc-linaro-4.9-2014.11-x86_64_arm-linux-gnueabihf.tar.xz

which will download the newest version on the time of writing this.

I keep downloaded tools in the /opt directory rather than in the /usr/local or other places in the /usr tree.

]$ cd /opt
]$ mkdir toolchains
]$ cd toolchains
]$ tar Jxvf ~/Downloads/gcc-linaro-4.9-2014.11-x86_64_arm-linux-gnueabihf.tar.xz
]$ ln -s gcc-linaro-4.9-2014.11-x86_64_arm-linux-gnueabihf/ gnueabihf
]$ file gnueabihf/bin/arm-linux-gnueabihf-gcc

These commands will create a toolchains directory in /opt and unpack the downloaded binaries into a structure. A symbolic link gnueabihf is created. This link can later be changed if a newer version of the compiler and libraries are downloaded.

The last command is just for ensuring that you've got the correct package downloaded. Expect something like this:

[klaus@klaus-x230 bin]$ file arm-linux-gnueabihf-gcc
arm-linux-gnueabihf-gcc: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked, interpreter 
/lib64/ld-linux-x86-64.so.2, for GNU/Linux 2.6.24, BuildID[sha1]=71722376ff3af9eee5caf7bdfa2ecc350db0a590, not stripped
[klaus@klaus-x230 bin]$ 

Develop a Cross Compiled Program

Start Eclipse and create a new project:

RemoteDebugging.png

Notice the settings for the Cross GCC

On one of the next dialogues you have to specify what the prefix for the cross compiler tools are and where they resides.

RemoteDebugging1.png

In the project create a new C source file and fill in some "Hello World" stuff.

Save and compile (Ctrl+S, Ctrl+B).

In a console go to <path to your project>/Debug

]$ file <your binary (project name)>

Expect something like this:

[klaus@klaus-x230 Debug]$ file TestRemoteDBG 
TestRemoteDBG: ELF 32-bit LSB executable, ARM, EABI5 version 1 (SYSV), dynamically linked, 
interpreter /lib/ld-linux-armhf.so.3, for GNU/Linux 2.6.16, BuildID[sha1]=e8baff7637d637533f3730021407ffdc6d4c314e, not stripped
[klaus@klaus-x230 Debug]$ 

This tells us that the compiler has produced ARM executable code.

Remote Debugging

In order to be able to debug remote the remote board needs a suitable gdbserver. There is one already onboard - or it can be downloaded using apt-get, but that one does not operate correct with the toolchain downloaded previously.

But luckily there is a suitable gdbserver included with the gnueabihf tools.

]$ scp /opt/gnueabihf/bin/gdbserver <username>@<your BBB IP>:~/

If you set-up password-less login over SSH (see this page for details) your life will be much easier.

You can test your newly developed ARM program on your BBB.

]$ scp <path to your project>/Debug/<yourbinary> <username>@<Your BBB IP address>:~

Log on to your BBB and try

]$ ./<yourbinary>

and inspect the output.

Next thing is to set up remote debugging.

In Eclipse select the Run menu and select Debug Configurations

RemoteDebugging2.png

First mark the C/C++ Remote debugging and then click on the new button to the upper left corner of the dialogue.

You'll get a dialogue like this:

RemoteDebugging3.png

Press the New button to the right of the Connection line.

This will open a dialogue for setting up the connection to the BBB. We'll use SSH.

RemoteDebugging4.png

You can use the local IP address or any other configured for the BBB.

RemoteDebugging5.png

Returning to the main Debug Configuration dialogue you'll see that the Connection now has been filled in with the details you just provided.

RemoteDebugging6.png

Next you'll have to specify the complete path of your program to execute on the BBB. The program will be sent over the SSH connection before launching the gdbserver - so any changes made on the development host will be reflected on the binary on the BBB.

Here I just placed the binary in my home directory, but it could be anywhere suitable.

RemoteDebugging7.png

Next thing to do is to click on the Debugger tab in the top of the dialogue. In this part of the settings you'll have to specify a complete path and name of the debugger - in this case we'll use the Linaro supplied residing in /opt/toolchains/gnueabihf

RemoteDebugging8.png

Also click on the Shared libraries tab and click Add and navigate to /opt/toolchains/gnueabihf/libc/lib and add that. This will remove some error messages during debugging.

RemoteDebugging16.png

Adjust the path to the gdbserver on the BBB.

RemoteDebugging15.png

You are now ready to debug. Press the Debug button.

RemoteDebugging9.png

You're asked a password for your login on the BBB.

RemoteDebugging10.png

And the you're told what system you're debugging.

RemoteDebugging11.png

And finally the debugger launches the program that has been transfered to the remote BBB and the gdbserver is launched with the program a a parameter and you can debug you application just like any other application.

This set-up has been heavily inspired by this site and the video by D. Molloy at YouTube.

Installing a new official Debian image on a SD card

Download from the BeagleBoard.org site or elsewhere a fresh image suitable for the BBB.

You will typically get a file named like this

bone-debian-7.8-lxde-4gb-armhf-2015-03-01-4gb.img.xz

Date and version number may vary.

In your download directory execute this command

]$ xz -dk bone-debian-7.8-lxde-4gb-armhf-2015-03-01-4gb.img.xz

this will unpack the image into a file like this

bone-debian-7.8-lxde-4gb-armhf-2015-03-01-4gb.img

Locate your SD card

Have a 4GB SD ready and inserted into your computer. Execute

]$ ll /dev/sd*

or

]$ ll /dev/mmcblk*

the way your computer interface to the SD card will either see it as a disk drive and name it /dev/sdN, where N is the next free letter - e.g. you have one disk already installed in your computer it is most likely sda[09], the next disk the system recognises will be sdb.

On my laptop when I use the SD slot directly in the laptop the system sees the SD card as a new mmc block device, hence the mmcblk name.

Another way to determine the name of the freshly inserted SD card is to execute

]$ ls -lart /dev

this will list the content of /dev in reverse order with the newest at the end of the list, i.e. at the bottom of your console.

Removing the SD card and rerunning the command will give you the final evidence to what the name is, since it is now missing in the list.

If the SD card i preformatted, which most are, you will see two - or more - devices like this

]$ ll /dev/mmcblk*
brw-rw----. 1 root disk 179, 0 May  1 13:15 /dev/mmcblk0
brw-rw----. 1 root disk 179, 1 May  1 13:15 /dev/mmcblk0p1
]$

The mmcblk0 is the main block device and the mmcblk0p1 is the first partition on the disk.

Transferring the image to the SD card

In order to transfer the disk image to the SD card first ensure that it is not mounted, e.g. by removing the card and re-insert it into the reader slot or by running a umount command (RTFM umount).

Next issue this command

]$ sudo dd if=bone-debian-7.8-lxde-4gb-armhf-2015-03-01-4gb.img of=/dev/mmcblk0 bs=1M

The dd command is a versatile utility that takes an input file (if) and an output file (of) and copies the input file to the output file (/dev/mmcblk0) in 1 mega bytes blocks (BS=1M). Expect 10 to 20 minutes before the command returns depending on the speed of your card reader and the SD card. Note here, that we use the main block interface file mmcblk0 not the mmcblk0p1 or the sdb not the sdb1.

When finished you will get a report like this

3700+0 records in
3700+0 records out
3879731200 bytes (3.9 GB) copied, 557.971 s, 7.0 MB/s

and your SD is ready to run in the BBB.

Starting the new image on BBB

Remove the SD card from your computer and insert it into the BBB.

Find the user button located just above the SD card slot.

Press and hold the button while applying power to the device. When the device starts to boot (blinking leds) release the user button.

If you have previously connected your BBB using the

]$ ssh root@192.168.7.2

you will probably get a message like this

]$ ssh root@192.168.7.2
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@    WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED!     @
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!
Someone could be eavesdropping on you right now (man-in-the-middle attack)!
It is also possible that a host key has just been changed.
The fingerprint for the ECDSA key sent by the remote host is
80:98:39:60:af:8e:db:14:47:9f:76:6a:88:89:12:e3.
Please contact your system administrator.
Add correct host key in /home/klaus/.ssh/known_hosts to get rid of this message.
Offending RSA key in /home/klaus/.ssh/known_hosts:49
ECDSA host key for 192.168.7.2 has changed and you have requested strict checking.
Host key verification failed.

which tells us that in the ~/.ssh/known_hosts file we keep a fingerprint of hosts that we have previously accepted to be legal computers to connect to. You have to edit the ~/.ssh/known_hosts file and remode the line(s) beginning with 192.168.7.2 and then try to connect once again.

First time you connect to your new image you will be prompted to verify the fingerprint of the connecion. Do that by typing yes.

Determine the version of your new image by issuing this command

root@beaglebone:~# uname -a
Linux beaglebone 3.8.13-bone70 #1 SMP Fri Jan 23 02:15:42 UTC 2015 armv7l GNU/Linux
root@beaglebone:~#

This is at the time of wirting the latest official supported image, but not necessarily the newest - you may find newer images floating around the Internet. The following device driver development will take outspring in the version.

Developing a device driver for the BBB

This section is heavily inspired by Derek Molloy's fine writing about device driver development.