Kemp's Blog

A technical blog about technical things

  • DeviceMaster protocol, part 2: UDP fields

    We ended the last post having split up the UDP scan/refresh response into individual fields, with each consisting of a value identifier, a length, and the actual content of the field. Now we come to deciphering the meaning of those fields.

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  • DeviceMaster protocol, part 1: UDP protocol

    The DeviceMaster range, at least with current firmware and drivers, uses a UDP-based protocol for discovery. The obvious first step, then, was to start Wireshark and log a few scans performed via PortVision DX. The Scan function within PortVision DX sent messages of the following form to the UDP broadcast address 255.255.255.255 on port 4606:

    a9 8d fd 53 7a 1c b0 de 00 00 2c 00 0c 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    

    A lot of zeros there, not much to go on. Performing more scans showed the the 0x2c in byte 11 was incrementing, so this was presumably a sequence number of some kind. Leaving PortVision DX open overnight showed that it was a 16 bit count in little-endian byte order. The 0x0c byte could be specifying a function—in this case a scan.

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  • DeviceMaster protocol, part 0: My device and software

    This is the first post of a short series describing my effort to reverse engineer the protocol used by Comtrol for their DeviceMaster range of Ethernet device servers. These allow RS-232/422/485 connected devices to be communicated with over an ethernet network.

    DeviceMaster RTS 8-Port DB9

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  • Error building grep for OpenEmbedded

    This is another error related to using a newer version of texinfo than expected. It’s also another “wait for it to fail and then edit in the working directory” solution unless someone can provide a better option.

    Once the build has failed with the following message:

    grep.texi:291: @itemx must follow @item

    open up $GUMSTIXTOP/tmp/work/x86_64-linux/grep-native-2.5.1-r2/grep-2.5.1/doc/grep.texi and delete lines 286 to 290 (inclusive). Side-effect: your generated documentation will no longer be perfect.



  • Error fetching packages for OpenEmbedded

    For my third post on compiling OpenEmbedded for Gumstix on a modern system, we come across errors downloading base-passwd, busybox, curl, dosfstools, fakeroot, file, gconf-dbus, git, iana-etc, ipkg, ipkg-utils, libxml-parser-perl, libxml2, mime-support, module-init-tools, netbase, openssl, pax-utils, pcmciautils, popt, pxaregs.c, setserial, sysvinit, tinylogin, tslib, udev, update-alternatives, update-rc.d, usbutils, util-linux, and zlib.

    This is a simple problem and a simple fix: old versions of these packages are either moved to a different location or removed entirely, so we change the URLs that the build process uses. Beware: using alternate sources for these packages carries an inherent risk – you may be downloading a modified version without knowing. Where possible you should also add hash entries for each file based on a known good value.

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  • gcc error building Python in OE

    This error message provides very little clue as to what the actual problem is when compiling Python during the OpenEmbedded build process:

    gcc: error: directory”: No such file or directory

    As it turns out (thanks to the tip here), this is caused by a change in subversion.

    Luckily it’s easy to inject your own copy earlier in the path than the one it usually finds. Simply create a script called svnversion in $GUMSTIXTOP/bitbake/bin and insert the following:

    #!/bin/sh
    echo exported
    

    Your problem should be solved.



  • Missing find.pl compiling OE

    I received the following error when compiling OpenEmbedded due to a file that is no longer included in Perl distributions:

    | Can’t locate find.pl in @INC (@INC contains: /etc/perl /usr/local/lib/perl/5.18.2 /usr/local/share/perl/5.18.2 /usr/lib/perl5 /usr/share/perl5 /usr/lib/perl/5.18 /usr/share/perl/5.18 /usr/local/lib/site_perl .) at perlpath.pl line 7.

    There are ways to integrate a copy of the file into the build process, but my inexperience with bitbake et al. meant that when they didn’t work I couldn’t troubleshoot very well myself. Instead, I simply placed the file in /etc/perl. The contents of the file, which should be called find.pl, can be found below.

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  • binutils errors compiling OE

    The second problem I encountered in building OpenEmbedded for our Gumstix devices was a failure when downloading binutils. Specifically, the checksum found for the downloaded file didn’t match the one that the build process expected. The message given is:

    NOTE: The MD5Sums did not match. Wanted: ‘9d22ee4dafa3a194457caf4706f9cf01’ and Got: ‘ccd264a5fa9ed992a21427c69cba91d3’
    NOTE: Task failed: Checksum of ‘ftp://ftp.gnu.org/gnu/binutils/binutils-2.18.tar.bz2’ failed
    NOTE: package binutils-cross-2.18-r1: task do_fetch: failed
    ERROR: TaskFailed event exception, aborting
    NOTE: package binutils-cross-2.18: failed
    ERROR: Build of /home/kemp/gumstix/gumstix-oe/org.openembedded.snapshot/packages/binutils/binutils-cross_2.18.bb do_fetch failed
    ERROR: Task 317 (/home/kemp/gumstix/gumstix-oe/org.openembedded.snapshot/packages/binutils/binutils-cross_2.18.bb, do_fetch) failed

    The error is due to an incompatibility between older versions of binutils and newer versions of texinfo. This post show you how to resolve this.

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  • patch version error compiling OE

    I have had to check out our Gumstix stock and find out if it’s still usable. They are a mix of old Connex and (non-Pro) Verdex boards and so the only OS I can build for them is OpenEmbedded. I have yet to find out if the currently available version from the Gumstix website actually works with these versions of the boards, but one step at a time…

    This post walks through how to solve the following error message when building OpenEmbedded on modern systems:

    | configure: error:
    | quilt requires at least version 2.4 of GNU patch. You can download a
    | current version of patch from ftp.gnu.org, or if you already have GNU patch
    | then you can supply its path with the ‘–with-patch=’ option.

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  • OpenModelica vs Dymola: connect

    In general, I target Modelica simulation at OpenModelica for the simple reason that it’s free for me to run anywhere. Having had to retarget one of the simulations at Dymola, I encountered a few differences. This post gives a quick overview of one such difference in using the connect function.

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