PDF - Two pages per page to one pages per page

So we had a PDF, it's size was 297 x 215 mm. Each page of this PDF contained two pages, like this:

 Page 1 of the input file                       Page 1 of output   Page 2 of output
    +------------------------------+            +---------------+  +---------------+
    |               |              |            |               |  |               |
    |               |              |            |               |  |               |
    |               |              |            |               |  |               |
    |               |              |            |               |  |               |
    |               |              |            |               |  |               |
    | Page 1        | Page 2       |            |   Page 1      |  |   Page 2      |
    |  of the book  |  of the book |            |    of the book|  |    of the book|
    |               |              |            |               |  |               |
    |               |              |            |               |  |               |
    |               |              |            |               |  |               |
    |               |              |            |               |  |               |
    |               |              |            |               |  |               |
    +------------------------------+            +---------------+  +---------------+
                                     +------->
 Page 2 of the input file            +------->  Page 3 of output   Page 4 of output
    +------------------------------+            +---------------+  +---------------+
    |               |              |            |               |  |               |
    |               |              |            |               |  |               |
    |               |              |            |               |  |               |
    |               |              |            |               |  |               |
    |               |              |            |               |  |               |
    | Page 3        | Page 4       |            |   Page 3      |  |   Page 4      |
    |  of the book  |  of the book |            |    of the book|  |    of the book|
    |               |              |            |               |  |               |
    |               |              |            |               |  |               |
    |               |              |            |               |  |               |
    |               |              |            |               |  |               |
    |               |              |            |               |  |               |
    +------------------------------+            +---------------+  +---------------+

So to do this, I extracted the left sides as page-0.pdf, and the right sides as page-1.pdf to the folder out, and the n joined these together:

#!/bin/bash
set -eux

# Default resolution is 720 dpi
# For points, use 72 dpi

# The actual pdf was 297 x 215 mm --(720 dpi)----> 8418 x 6094 pixels
# I only want to extract half of it -------------> 4209 x 6094
# For the right page, I need an offset -(72 dpi)-> -421.0 0

INPUT_FILE="$1"

rm -rf ./out
mkdir out

ghostscript -o "out/%d-0.pdf" -sDEVICE=pdfwrite -g4209x6094 \
-c "<</PageOffset [0 0]>> setpagedevice" -f "$INPUT_FILE"

ghostscript -o "out/%d-1.pdf" -sDEVICE=pdfwrite -g4209x6094 \
-c "<</PageOffset [-421.0 0]>> setpagedevice" -f "$INPUT_FILE"

ghostscript -o "singlepage-$INPUT_FILE" -sDEVICE=pdfwrite -dPDFSETTINGS=/ebook \
    $(ls out/* | sort -V)

rm -rf ./out

References:
http://superuser.com/questions/54054/convert-pdf-2-sides-per-page-to-1-side-per-page

Back to school - Coursera - Crypto, Control Theory, Android

After KR told me that he signed up for a Cryptography course on Coursera, I decided to do the same. I learned crypto at Uni, but that was a long time ago, so I thought, it's time to refresh my memories. The story does not end here, as this weekend, I signed up to two more courses: an Android course, and a Robot Control course. I'm a bit behind at the moment for each of the courses. I find this Coursera amazing, and I hope my wife won't kill me before I finish these courses. Should you be interested, here is a list of the courses that I started:

• https://class.coursera.org/crypto-009
• https://class.coursera.org/conrob-002
• https://class.coursera.org/android-001

I just started to watch the video lectures for the Android class, and watching this video atm as recommended by the professor:

Ubuntu - change dns server for proxychains

This is really a not for myself, so that I don't forget it. So if you are using proxychains to access some servers through a proxy, you might want to use that system's dns server. In that case, presuming that you are running ubuntu, please modify the file:

/usr/lib/proxychains3/proxyresolv

When you open the file, it will be obvious what needs to be changed.

Cross compiling uwsgi with buildroot

I really like uwsgi, and would like to see it on my raspberry PI, so I decided to create a buildroot environment, and add uwsgi as a package. It means cross compiling uwsgi. In this blog, I will log the process.
One thing to note, that the text was shortened with:

s,/data/matelakat/repa/.workspace/buildroot-2013.05,$BUILDROOT,g

Let's check out a tagged version

git checkout tags/1.9.9 -B build-fixes

And make sure, it builds on the host system:

make
...
############## end of uWSGI configuration #############
*** uWSGI is ready, launch it with ./uwsgi ***

Cross compilation

First, I set the compiler and the precompiler, as suggested by Roberto:

CC="$BUILDROOT/output/host/usr/bin/arm-unknown-linux-gnueabi-gcc" \
CPP="$BUILDROOT/output/host/usr/bin/arm-unknown-linux-gnueabi-cpp" make

I got this error (newlines inserted for readability)

*** uWSGI linking ***
$BUILDROOT/output/host/usr/bin/arm-unknown-linux-gnueabi-gcc -o uwsgi ...
...
plugins/transformation_chunked/chunked.o -lpthread -lm -rdynamic -ldl -lz 
-L/usr/lib/x86_64-linux-gnu -lpcre -luuid -lssl -lcrypto 
-L/usr/lib/x86_64-linux-gnu -lxml2 -lpthread -ldl -lutil 
-lm /usr/lib/python2.7/config/libpython2.7.so -lutil -lcrypt
/data/matelakat/repa/.crosstool/x-tools/arm-unknown-linux-gnueabi/lib/gcc/
arm-unknown-linux-gnueabi/4.8.2/../../../../arm-unknown-linux-gnueabi/bin/
ld: skipping incompatible /usr/lib/x86_64-linux-gnu/libpthread.so when searching for -lpthread
/usr/lib/x86_64-linux-gnu/libpthread.a: could not read symbols: File format not recognized
collect2: error: ld returned 1 exit status
*** error linking uWSGI ***
make: *** [all] Error 1

That seems to be an issue, my host system's libpthread will definitely fail to link with the arm binary. I added a print statement, and an assert False.

*** uWSGI linking ***
['-lpthread', '-lm', '-rdynamic', '-ldl', '-lz', '-L/usr/lib/x86_64-linux-gnu -lpcre',
 '-luuid', '-lssl', '-lcrypto', '-L/usr/lib/x86_64-linux-gnu -lxml2', '-lpthread',
 '-ldl', '-lutil', '-lm', '/usr/lib/python2.7/config/libpython2.7.so', '-lutil', '-lcrypt']
Traceback (most recent call last):
  File "uwsgiconfig.py", line 1220, in 
    build_uwsgi(uConf(bconf))
  File "uwsgiconfig.py", line 401, in build_uwsgi
    assert False
AssertionError
make: *** [all] Error 1

It seems to be using my host's libpython2.7.so. But that's not the point (now). The real point is the '-L/usr/lib/x86_64-linux-gnu -lxml2' part. I need to find out from where does it come. I need to add some additional breakpoints. As my computer has 2 CPU cores, uwsgi build employs a compile queue. For now, as I would like to debug things, I want to run the build sequentially, so that it is easier to follow what's happening. So I cleaned the build, and set the CPUCOUNT environment variable:

CC="$BUILDROOT/output/host/usr/bin/arm-unknown-linux-gnueabi-gcc" \
CPUCOUNT=1 \
CPP="$BUILDROOT/output/host/usr/bin/arm-unknown-linux-gnueabi-cpp" make

I created a shell script with these contents. The libs variable is used to collect the libraries during plugin compilation. Let's add a print statement to see when we modify this array

./doit.sh  | grep ADDING
...
[ADDING LIBRARY] ['-lpthread', '-ldl', '-lutil', '-lm',
 '/usr/lib/python2.7/config/libpython2.7.so', '-lutil']
...

Oh, that doesn't look good, I bet, that's the python plugin. Let's print out the plugin's name as well

./doit.sh  | grep ADDING
...
[ADDING LIBRARY - python] ['-lpthread', '-ldl', '-lutil',
 '-lm', '/usr/lib/python2.7/config/libpython2.7.so', '-lutil']
...

Okay, shelve it for now, and go back to the original problem, see from where does the '-L/usr/lib/x86_64-linux-gnu -lxml2' line come from. That might be lxml. It seems, that xml2-config --libs is called to detect the library path. The host's binary was called this time, instead of the cross tool's. So let's add the crosstool bin path to the path:

#!/bin/bash

set -eux
PATH="$BUILDROOT/output/host/usr/arm-buildroot-linux-gnueabi/sysroot/usr/bin:${PATH}" \
CC="$BUILDROOT/output/host/usr/bin/arm-unknown-linux-gnueabi-gcc" \
CPUCOUNT=1 \
CPP="$BUILDROOT/output/host/usr/bin/arm-unknown-linux-gnueabi-cpp" make

But as I modified my script, I ended up with this error:

python uwsgiconfig.py --build
$BUILDROOT/output/
host/usr/arm-buildroot-linux-gnueabi/sysroot/usr/bin/
python: 1: $BUILDROOT/
output/host/usr/arm-buildroot-linux-gnueabi/sysroot/usr/bin/python: 
Syntax error: word unexpected (expecting ")")
make: *** [all] Error 2

It's not an x86 executable:

file $BUILDROOT/output/host/usr/arm-buildroot-linux-gnueabi/sysroot/usr/bin/python
$BUILDROOT/output/host/usr/arm-buildroot-linux-gnueabi/sysroot/usr/bin/python: symbolic link to `python2'
file $BUILDROOT/output/host/usr/arm-buildroot-linux-gnueabi/sysroot/usr/bin/python2.7
$BUILDROOT/output/host/usr/arm-buildroot-linux-gnueabi/sysroot/usr/bin/python2.7:
 ELF 32-bit LSB executable, ARM, version 1 (SYSV), dynamically linked (uses shared libs),
 for GNU/Linux 3.2.48, not stripped

that's why I have issues with that python. So I modify my shell script to start a host python built by buildroot:

#!/bin/bash

set -eux
PATH="$BUILDROOT/output/host/usr/arm-buildroot-linux-gnueabi/sysroot/usr/bin:${PATH}" \
CC="$BUILDROOT/output/host/usr/bin/arm-unknown-linux-gnueabi-gcc" \
CPUCOUNT=1 \
CPP="$BUILDROOT/output/host/usr/bin/arm-unknown-linux-gnueabi-cpp" \
$BUILDROOT/output/build/host-python-2.7.3/python uwsgiconfig.py --build

Note, that I also left out the make, and am directly calling uwsgiconfig.py. This is the next error that I get:

*** uWSGI linking ***
...
$BUILDROOT/output/host/usr/lib/libz.so: file not recognized: File format not recognized
collect2: error: ld returned 1 exit status
*** error linking uWSGI ***

file $BUILDROOT/output/host/usr/lib/libz.so.1.2.7 
$BUILDROOT/output/host/usr/lib/libz.so.1.2.7:
 ELF 64-bit LSB shared object, x86-64, version 1 (SYSV), dynamically linked,
 BuildID[sha1]=0x5bbf6ecd4880bbbbb73c57e048dba2d36aa299e0, not stripped

well, that's interesting. That file is in the host directory, that's a host module of course. Maybe the library path is wrong?

*** uWSGI linking ***
['-lpthread', '-lm', '-rdynamic', '-ldl', '-lz',
 '-L$BUILDROOT/output/host/usr/arm-buildroot-linux-gnueabi/sysroot/usr/lib -lpcre',
 '-luuid', '-lssl', '-lcrypto', '-lxml2 -lz -lm -ldl', '-lpthread', '-ldl',
 '-lutil', '-lm', '-lpython2.7', '-lcrypt']

There is the pcre library, which looks suspicious. So I added another entry to the path, which will find the target system's pcre config script.

#!/bin/bash

set -eux
PATH="$BUILDROOT/output/build/pcre-8.32:$BUILDROOT/output/host/usr/arm-buildroot-linux-gnueabi/sysroot/usr/bin:${PATH}" \
CC="$BUILDROOT/output/host/usr/bin/arm-unknown-linux-gnueabi-gcc" \
CPUCOUNT=1 \
CPP="$BUILDROOT/output/host/usr/bin/arm-unknown-linux-gnueabi-cpp" \
$BUILDROOT/output/build/host-python-2.7.3/python uwsgiconfig.py --build

The problem is still there. Let's look at the build output again:

** uWSGI linking ***
['-lpthread', '-lm', '-rdynamic', '-ldl', '-lz', '-lpcre', '-luuid',
 '-lssl', '-lcrypto', '-lxml2 -lz -lm -ldl', '-lpthread', '-ldl',
 '-lutil', '-lm', '-lpython2.7', '-lcrypt']
...
$BUILDROOT/output/host/usr/bin/arm-unknown-linux-gnueabi-gcc -o uwsgi -L$BUILDROOT/output/host/usr/lib
...

I need to find out from where does that come. As a first guess, I am printing out ldflags.

LDFLAGS ['-L$BUILDROOT/output/host/usr/lib']

That could be an issue. Let's try to find out which plugin is doing this.

./doit.sh | grep LDFLAG
...
[ADDING LDFLAG - python] ['-L$BUILDROOT/output/host/usr/lib']
...

As I looked at plugins/python/uwsgiplugin.py, found the include issue, and the libs. So I decided to do a really dirty hack to override libs (It's getting late here) That left me with another issue:

plugins/python/python_plugin.o: In function `init_uwsgi_embedded_module':
python_plugin.c:(.text+0x1d6c): undefined reference to `Py_InitModule4_64'
collect2: error: ld returned 1 exit status

Let's hack the include directory as well, maybe that is causing the issue. as I was there, I also hacked the library paths. And this is my reward:

make clean
./doit.sh
...
############## end of uWSGI configuration #############
*** uWSGI is ready, launch it with ./uwsgi ***

ICS - mexamine

First, start xboard as an ics client:

xboard -ics -icshost freechess.org

I am assuming, that both players, a and b started xboard, and logged in. In order to examine a chess game together with a friend of yours, issue the following commands (The a: part is indicating which player is entering the command):

a: examine

This will print out the game id. In my case, it is 194. Now, the other player needs to observe that game

b: observe 194

Now, we are observing the game with player B. The next step is to enable mexamine:

a: mexamine b

After this, both player are examining the same game. To end the examination:

a: unexamine

Direct PCB prints + etch

I printed some sample patterns with my solid ink printer to PCB, and etched them. I am pleased with the results. I think I will need a better etch fluid (more fluid or more concentrated fluid). Here you go:

source for the patterns

Direct PCB printing with Xerox Phaser 8400

Almost a year ago, I purchased a beautiful Xerox Phaser 8400 with 250000 pages already printed, because I wanted to try out the direct PCB printing method. I purchased some "pyralux" blank PCBs from here: Tech-place. Now, after one and a half year, it is time to try out what is possible.

• Paper/PCB Size
  The size of the PCB is around 150mm x 115mm. The Xerox manual says, that the minimum paper size should be: 75mm x 127mm - I am in the range, so that's good. My PCB is bigger than an A6.
• Which Side Gets the Ink:
  It is an experiment. You load a paper with a writing on it, and print something on it. The ink goes to the back of the paper, so I will need to load my PCB with the copper facing down.
• Paper/PCB Thickness
  In theory, the width of the PCB is 150um. So I looked up the supported papers in the manual, and searched for the thickest one was: Phaser Professional Solid Ink Business Cards, 225 g/m2 (80 lb. Cover) Now I needed to map this information to a thickness. Unfortunately, I failed to find a datasheet for that paper. However, I found this chart which basically tells me that 150 um is around 110 g/m2. I am convinced, my PCB will fit in, this beast can deal with 225g/m2 paper.
• Print
  The print was successful, see this photo:
  
  
  And, if you want to see a video of the steps above, be my guest: