Thursday, April 03, 2014

Waiting for the network to be up on the BeagleBone Black

It finally hit me today as I was reading over this article, and it should have hit me sooner. The article mentions that in order to get past the network startup hurdles in systemd, you need to wait on the NetworkManager service. However, I use connman. It didn't occur to me until today that they provide exactly the same functionality, and I just needed to swap one with the other. Now,  I have all my network dependent programs simply After=connman.service in the systemd service descriptor files, and they're golden.

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ImportError: No module named pkg_resources when trying to use pip on the BeagleBone Black

I've recently been trying to use Python on the BeagleBone Black, for a number of reasons:

  1. I want to learn a new language which could be useful to me in another job in the future (and this job, even better!)
  2. Given all the effort I've put into making our embedded systems work on multiple platforms, I think I've finally got enough infrastructure in place that we can start leveraging other cross platform products to shorten up our development time.
  3. As a scripting language capable of using bindings to other languages, Python should help me create very functional code that doesn't need extremely high performance in a very short amount of time and reduce my development time for complicated tasks.
Unfortunately, like many other things on the BeagleBone Black, things aren't going as well or as simply as you'd think they should at first glance. For starters, the pip package manager for Python isn't installed by default on the BeagleBone Black (at least not as of the 2012.12 image). So, I had to install that first:

opkg install python-pip

When I tried to run the package manager, I ran into the following error:

Traceback (most recent call last):
  File "/usr/bin/pip", line 5, in
    from pkg_resources import load_entry_point
ImportError: No module named pkg_resources

After Googling around for a bit, I found these questions on Stack Overflow. Apparently you must also have the setuptools package installed in order to be able to use pip because it's not a simple package manager like apt in Ubuntu. It's more like emerge in Gentoo, where it downloads code packages and is capable of compiling them and performing custom installations. Fortunately, there's an opkg package for that:

opkg install python-setuptools

After that was installed, it became a simple matter of finally importing the actual package that I originally wanted that started all of this:

pip install psutil

... the process utils library for Python

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Friday, March 21, 2014

Undefined reference to `log' when compiling on Ubuntu 13.10 with gcc

After I upgraded to Ubuntu 13.10, I inexplicably started getting errors in a build that had been perfect for a very long time. It turned out, there was a significant change in the linker and a bug introduced. The fix is described beautifully on this blog post, but for convenience sake:

Add '-Wl,--no-as-needed' to your LDFLAGS

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Monday, March 17, 2014

Slow login times in Ubuntu 13.10 (not just SSH)

I recently setup a new install of Ubuntu 13.10 for a server and found that a lot of my login times were slow when remotely logging in (and not just via SSH). The culprit turned out to the the /etc/nsswitch.conf file:

This line:
hosts: files mdns4_minimal [NOTFOUND=return] dns mdns 4 mdns

Should be changed to this line:
hosts: files dns

... to resolve the issue

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Thursday, March 13, 2014

Developing a cape for the BeagleBone (Black)

Due to the needs of our company, we're developing an in-house cape for the BeagleBone Black to integrate it with our equipment. Yes, there are numerous capes already in existence, but they each provide a singular function that would require stacking in combination with other capes to meet our needs. Additionally, it increases the number of external vendors on which we must rely to meet our demands. Instead, we've chosen to create a custom cape that has multiple extensions on the same cape and integrates nicely with our existing board stacks. Unfortunately, I'm not that familiar with BeagleBone Black capes, so I'm going to be learning how to create the software necessary for a new cape and configure it using the Device Tree system on the BeagleBone Blacks. I'll be tracking my progress and things that I've learned on this blog for my own future reference and hopefully it'll even help out somebody else.

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Friday, January 31, 2014

Recovering the root password on a BeagleBone Black

I recently went to use a BeagleBone Black board on which I'd never booted from the eMMC before (that I could recall) and had been instead booting off of a microSD card. To the best of my knowledge, the root password on this board should never, ever have been changed from the default (blank password), but apparently it was. None of the passwords that I had ever used for any of my BeagleBone Blacks was working, which created a problem: I needed to recover the root password to this BeagleBone Black so that I could use it for my projects again. I was in luck. The BeagleBone Black has the tools that I needed to do it. I'm writing this blog post (like many other posts in the blog) so that I can have a reference to come back to if I ever need it in the future.

To recover the root password of a BeagleBone Black, you'll need the following items:

  • A 5V, minimum 1 A dedicated power source (you shouldn't really be powering the board off of the micro USB port)
  • An SD card (and reader, of course)
  • An FTDI USB-to-serial cable for accessing the debug serial port of the BeagleBone Black.
Once you've acquired all of the required items above, perform the following steps:

  1. Flash the SD card with an image that you can obtain from
  2. Insert the SD card into the *unpowered* BeagleBone Black.
  3. Apply power.
  4. The BeagleBone Black should boot from the SD card (assuming that you've flashed the correct image)
  5. Connect the FTDI serial cable to the board and your compter, and open your serial client of choice to connect to the board.
  6. Hit enter once or twice, and a command prompt should come up, assuming you've used the correct settings:
    1. 115200
    2. 8N1
  7. Log in using root and a blank password (should be the default on the SD card image that you downloaded from the website.)
You're now logged into the image running on the SD card. However, we can't change the root password now because that will only change it for the root user on the SD card image. We need to change it for the permanent image stored on the BeagleBone Black's embedded eMMC flash. Being logged in as you are, perform the following steps to mount the eMMC image and change the password for that image's root user:

  1. Mount the eMMC flash:  mount /dev/mmcblk1p2 /media/card
  2. Change the root of the file system to be the partition on the eMMC flash which you just mounted: chroot /media/card
  3. Change the password of the root user to something you know: passwd root
  4. Exit out of the changed root: exit
  5. Shutdown the BeagleBone Black : shutdown -h now
  6. Disconnect the power from the board
  7. Eject the microSD card.
  8. Reconnect the power to the board
  9. Watch the board boot up, and log in as root. You should be able to log in with the password that you just set.

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Implicit rules with Makefile

In my ongoing quest to make my builds less complex and faster, I've been going through my Makefiles and trying to learn as much as possible to simplify it and leverage Make as much as I can. To that end, I discovered something incredibly useful today that I suppose I would have known had I taken the time to read the man page for Make:

make -p

This command will list all of the implicit rules for make, which you can then use to optimize the living crap out of your Makefile.

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Thursday, January 02, 2014

Installing NTP on an Ubuntu server

NTP is used to synchronized time between machines. You can read the Ubuntu HOWTO here.

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Installing a TFTP server using xinetd on Ubuntu

I recently had need to redo an old server that had been running an ancient Gentoo installation for which there was no longer a software upgrade path, so I chose to install Ubuntu on it. Part of the requirements of the server were that it runs a TFTP server for hosting files for configuring embedded devices. I had previously found an article on how to setup TFTP through inetd, but I could find it, so I'm cobbling this tutorial together from various sources.

  1. # apt-get install xinetd tftpd
  2. Ensure that the following lines are in the /etc/services file:
    1. tftp     69/tcp
    2. tftp     69/udp
  3. Open the /etc/xinetd.d/tftp file (create it if it doesn't exist) and ensure that it contains the following:
    # default: off
    # description: The tftp server serves files using the Trivial File Transfer \
    #    Protocol.  The tftp protocol is often used to boot diskless \
    #    workstations, download configuration files to network-aware printers, \
    #    and to start the installation process for some operating systems.
    service tftp
        socket_type     = dgram
        protocol        = udp
        wait            = yes
        user            = root
        server          = /usr/sbin/in.tftpd
        server_args     = -s /tftpboot
        disable         = no
  4. # /etc/init.d/xinetd restart
  5. Test the server:# tftp localhost
    tftp> get hello.txt
    Received 23 bytes in 0.1 seconds
    tftp> quit 
You should now be good to go. The (abridged) instructions for this were retrieved from this article.

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Wednesday, November 13, 2013

Digging into Raspberry Pi: Part 2

So, further into my quest to build a control system with the Raspberry Pi, I've been looking around at ways to have simple input from the user for a simple system. The first thing that came to my mind was using an Xbox controller to provide input from the user:

  • It's simple for the user to use, and given that many people grew up with game consoles, it'll be intuitive and not require retraining the user.
  • The Xbox controller plugs into USB and should therefore provide an easy way to integrate a controller for my system.
  • The command to download joystick support for the Raspberry Pi was dead simple: 
    • sudo apt-get install joystick
The post located here also shows some options for the joystick on the Raspberry Pi. I'll post more information as I learn how to use the library to access the device.

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