All sorts of nitty-gritty technical things.
I came across this good article about how to program general purpose IO (GPIO) from user space code in Linux
http://falsinsoft.blogspot.ie/2012/11/access-gpio-from-linux-user-space.html
It contains a nice little synopsis of the steps involved with setting up and reading & writing inputs and outputs!
This is a classic, a venerable magento database was presented to me today – it had grown over time to 10GB and was in danger of being booted right off its hosting due to its wide girth! I’d say cron hadn’t been run for years.
Anyway its very easy to clean up the magento database, most of the data bloat is stored in a group of log tables and can be just delete right away by running the following queries on the DB:
truncate log_customer; truncate log_quote; truncate log_summary; truncate log_summary_type; truncate log_url; truncate log_url_info; truncate log_visitor; truncate log_visitor_info; truncate log_visitor_online;
This reduced the DB size from 10GB to about 150MB.
I had a very strange (and annoying problem) with an OpenCV project in VS2012, when my program created an image display window (namedWindow) I noticed that its window title was all garbled and soon afterwards other display windows were created even though the code had not requested them.
I spent a lot of time comparing the VS2012 projects settings with those of another working project and eventually found that I could make the problem go away by adding this to the ‘Preprocessor Definitions’ setting:
_ITERATOR_DEBUG_LEVEL=0
I have no idea at the moment why adding this fixed the problem but it did! I must have added it to the working project (which was born inside VS2010) but I can’t remember why!
I had a bit of trouble getting some Android VNC viewers to connect to a Real VNC server on windows 7 today. The most common error message proffered by the viewers while trying to connect was:
Server did not offer supported security type
It seems this may be caused by Real VNC using some non-standard VNC extensions…
Anyway I found that I could get rid of the error message and get the VNC connections to work correctly by changing the following Real VNC Settings (see screen-shot below):
(a) Change ‘Authentication’ to ‘VNC Password’ (and configure a password)
(b) Change ‘Encryption’ to ‘Prefer on’
Note that the second change probably results in the connection being unencrypted so be careful if you are using this on a public network!
This is a record of how I built lighttpd with pcre for ARM. Most examples of cross compiling lighttpd for ARM do not include pcre, but to get the best out of lighttpd you really do need pcre built in. So we first need to get and cross compile pcre and then lighttpd.
Build pcre for ARM
In this example I assume that you create the build directories in you home directory, e.g. /home/youruser/ , you will need to change this in the following commands to match your actual directory set-up.
cd /home/youruser mkdir buid_pcre cd build_pcre wget ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre/pcre-8.21.tar.gz tar -xzf pcre-8.21.tar.gz cd pcre-8.21 ./configure --host=arm-linux-gnueabi CC=arm-linux-gnueabi-gcc \ AR=arm-linux-gnueabi-ar STRIP=arm-linux-gnueabi-strip \ RANLIB=arm-linux-gnueabi-ranlib \ --prefix=/home/youruser/build_lighttpd/build_pcre/_install make make install
This should build pcre and install the output files into the following directory:
/home/youruser/build_lighttpd/build_pcre/_install
Change this path to suit your own needs.
Build lighttpd for ARM
Now that we have build pcre we can build lighttpd as follows, there is a bit of trickery involved for getting it to build with pcre, but happily this article showed me the way (thanks)!
cd /home/youruser mkdir build_lighttpd cd build_lighttpd wget http://download.lighttpd.net/lighttpd/releases-1.4.x/lighttpd-1.4.32.tar.gz tar -zxvf lighttpd-1.4.32.tar.gz cd lighttpd-1.4.32 ./configure -prefix=/home/youruser/build_lighttpd/_install \ -host=arm-linux-gnueabi CC=arm-linux-gnueabi-gcc \ RANLIB=arm-linux-gnueabi-ranlib STRIP=arm-linux-gnueabi-strip\ --enable-shared --without-mysql --without-zlib --without-bzip2 \ --disable-ipv6 \ PCRECONFIG=/home/youruser/build_lighttpd/build_pcre/_install/bin/pcre-config \ PCRE_LIB=/home/youruser/build_lighttpd/build_pcre/_install/lib/libpcre.a \ CFLAGS="$CFLAGS -DHAVE_PCRE_H=1 -DHAVE_LIBPCRE=1 -I/home/youruser/build_lighttpd/build_pcre/_install/include" make make install
Again remember to change: /home/youruser/ in each case.
If the build succeded, all the files that you need to install lighttpd on your target ARM device should be under: /home/youruser/build_lighttpd/_install
Here is an article which talks about how to manually install lighttpd.
But at a very minimum you need to:
(a) Download and edit the config file – lighttpd.conf
(b) Copy the pcre libs to /usr/lib or similar – libpcre.so.0 , libpcre.so.0.0.1
(c) Copy on the lighttpd binary from: /home/youruser/build_lighttpd/_install/sbin
(d) Copy on the lib folder from /home/youruser/build_lighttpd/_install/lib
(e) Run lighttpd specifying the paths to config file and lib folder, for example:
lighttpd -D -f /etc/lighttpd/lighttpd.conf -m /usr/lib
Thanks to the following articles for the build info!
http://fengh2000.blogspot.ie/2009/06/how-to-cross-compile-lighttpd-with-pcre.html
http://stackoverflow.com/questions/12079498/lighttpd-refernces-wrong-lib-location
I had some difficulty today getting my code to link to boost::filesystem::copy_file() (linking to boost version 1.53.0, gcc v4.7.2), I suffered from link errors like this:
undefined reference to `boost::filesystem::detail::copy_file(boost::filesystem::path const&, boost::filesystem::path const&, boost::filesystem::copy_option, boost::system::error_code*)’
From reading this post, it seemed that my problem may have stemmed from my use of c++0x.
None of the suggested solutions in this thread worked for me & I double checked that had built boost with -std=c++0x.
In the end after looking through the code in filesystem/operations.hpp the only thing that fixed my linking problem was to #define BOOST_NO_CXX11_SCOPED_ENUMS before including
#define BOOST_NO_CXX11_SCOPED_ENUMS #include
This may well not be the best/proper way to fix the problem but it was the only thing that worked for me..
Other relevant links that I found are here, here and here.
This article outlines the steps necessary for building OpenCV for a Linux ARM target. OpenCV is an open-source, cross-platform computer vision and machine vision library.
I cross compiled OpenCV for a Xilinx Zinq ARM system yesterday by more-or-less following the steps outlined in the above document – I had to change a few things to get the build to work. I am documenting the exact steps that I took in case anybody is having trouble (probably future me!).
I started with a fairly clean Ubuntu install on a virtual machine (it already had git installed) , first I installed some build tools, feel free to skip any that you already have:
sudo apt-get install build-essential sudo apt-get install cmake
Then I installed the GNU ARM tool-chain:
sudo apt-get install gcc-arm-linux-gnueabi sudo apt-get install g++-arm-linux-gnueabi
This installed version 4.7 of the compilers while the build process calls for version 4.6, to get around this I modified the cmake platform file slightly, see below.
Create a build directory, cd into it and get the OpenCV source from github:
mkdir opencv_build cd opencv_build git clone https://github.com/Itseez/opencv.git
To fix the version problem I modified the compiler version in the platform file (this may not be the most correct way to do this but it worked for me!):
I edited this file:
./opencv/platforms/linux/arm-gnueabi.toolchain.cmake
I changed the GCC_COMPILER_VERSION variable’s value from 4.6 to 4.7 to match my installed compiler. I had to edit the file as I wasn’t able to override these variables from the command line.
Now create a sub-directory called build and cd into it:
mkdir build cd build
And configure the build:
cmake -DSOFTFP=ON -DCMAKE_TOOLCHAIN_FILE=../opencv/platforms/linux/arm-gnueabi.toolchain.cmake ../opencv
This should complete without errors if you have the compiler that it is looking for installed etc.
Now run ‘make’ and ‘make install’:
make make install
Make will take a few minutes to run, make install should copy the output files to a subdirectory called ‘install’.
All being well you should now have all the include and lib files that you need to build an OpenCV app for your ARM device.
I am taking this opportunity to document a cross compilation procedure for libjpeg targeting ARM Linux mostly so that I won’t have to go searching for it again in the future!
mkdir libjpeg_build cd libjpeg_build
Now get the source and un-tar it:
wget http://www.ijg.org/files/jpegsrc.v9.tar.gz tar -xzvf jpegsrc.v9.tar.gz
Configure the build, specifying your C compiler and cross compilation host, then make:
./configure --host=arm-xilinx-linux CC=arm-xilinx-linux-gnueabi-gcc make
Here, I am using the xilinx build of the compiler, hence the reference to xilinx in the host and CC parameters, if I wasn’t using the xilinx tools the above configure command may have looked more like this:
./configure --host=arm-linux CC=arm-linux-gnueabi-gcc
Now make install, specifying a directory for the output:
make install DESTDIR=./_install
If all goes well the output of the build process should be written to the _install directory, copy the .so files to the appropriate directory on your target device (e.g. /usr/local/lib)
If you are using the easy social module in drupal 6 with a quirky (read rubbish) theme (or sometimes ubercart) then you may notice that the social media buttons don’t get displayed on some node types.
To get around this problem you may have to alter the node’s template to manually insert the Easy Social module’s output – and hence the social media buttons. Add the following to the relevant node template which can be found in your theme folder:
easy_social ;?>
More information can be found here.
PS It’s high time you were using drupal 7! ;-)
If you are scratching your head about how to setup Eclipse and CDT to use the boost thread library then have a look at the first post in this thread:
http://www.eclipse.org/forums/index.php/m/787571/
It explains which project settings need to be changed.
Thanks to Robert!