====== [hemmerling] Linux 8/8 - Useful Commands & Tricks ======
Related page:
  *[[booting.html|Booting from Devices]].
  *[[android.html|Google Android]].
  *[[linux.html|Linux 1/8]].
  *[[linux02.html|Linux 2/8 - Linux Distributions]].
  *[[linux03.html|Linux 3/8 - Linux Boot Loaders, Linux Build Systems, Linux Installers and Linux Implementors]].
  *[[linux04.html|Linux 4/8 - Linux Applications, Linux Tools and Linux Drivers]].
  *[[linux05.html|Linux 5/8 - SUSE 7.1 Linux on Clevo 2700c Notebooks with SIS630S Chipset]].
  *[[linux06.html|Linux 6/8 - Linux with X-Terminals and Terminals]].
  *[[linux07.html|Linux 7/8 - Linux on X86, X64 and ARM Computers]].
  *[[lpicone.html|Linux LPIC-1]].
  *[[lpictwo.html|Linux LPIC-2]].
  *[[linuxskills.html|Linux Skills & Skill Certification]].


===== Machine-specific Programming on Linux =====
==== uio Framework ====
  *The "uio framework" is suitable to avoid Linux license problems for Linux applications with simple, but machines-specific i/o - You may access any memory-mapped hardware by user applications, but you must not provide your source code for any drivers, as there is just a standard Linux mainline driver "mmap" :-).
  *You may not access legacy and classical PC hardware ( e.g. printer port,.. ) which is connected to the special Intel i/o hardware ports.
  *There is a special patch available at [[http://git.denx.de/|Git repository of DENX Software Engineering]] for Linux kernel 3.8 to allow the necessary device tree binding by command line  commands - this was "missing link" before. It is expected that this option becomes a standard feature of Linux Kernel 3.10, hopefully :-).
==== Select() / Poll() Framework ====
  *"include <sys/select.h>".
  *Poll() is a variation of Select().
  *Suitable to work with the "uio framework" and it's "mmap" function, to provide interrupt-driven data transfer with any memory-mapped hardware, without the need for thread programming, and it's overhead.
  *Loop operation:
    -Select() expects an array of file selectors as input.
    -It will got to sleep.
    -In case of a change of the contents linked with the file descriptors, Select() wakes up again.
    -The application which uses Select() has to explore and find out, which file descriptor contents changed.
    -The application handels the file descriptor ( read or writes data,.. ).
    -End-of-loop.
==== Gpio on Lemonboard ====
  *On the [[http://www.lemonboard.org/|Lemonboard]] with Ubuntu Linux / Linux, show Gpio Pins:
<code>
cat /sys/kernel/debug/gpio
</code>
  *Set Gpioi LED Value:
<code>
echo "1" > /sys/class/gpio/gpio203/value
echo "0" > /sys/class/gpio/gpio2/value
</code>
  *Additionally, there is a small application "gpioin". Config the GPIO CSI0_DAT12 to INPUT:
<code>
echo in > /sys/class/gpio/gpio158/direction
echo 1 > /sys/class/gpio/gpio158/active_low
echo falling > /sys/class/gpio/gpio128/edge
./gpioin /sys/class/gpio/gpio158/value
</code>

==== The Effect ====
  *You may now control hardware, even interrupt-driven hardware, from your Linux applications written in high-level language, e.g. C/C++, Python, Perl, Java, running on a standard Linux Kernel 3.10 ( or patched Linux Kernel 3.8 ). 
  *For comparison,, with Python and "Raspberry Pi" platform, you need a special Python library...
===== Linux Commands for Embedded Linux Boards =====
  *"cat /proc/cpuinfo".
  *"ls - l /proc/cpuinfo".
  *"file hello-world".
  *"printenv".
  *For successful use of aa remote NFS filesystem as "root" filesystem, the Linux server option "no_root_squash" is necessary. By this, "root" is not handled as unprivileged user, but the server believes that a true "root" wants to access.
  *For cross-compilation, add  a variable ( e.g. $Cross_compile ) to your makefiles, and define $Cross_compile as environment variable on your host. So that you may use the same makefile to compile both on host and target, but just use a environment variable to create the name of the cross-compiler from the name of the native compiler. So no if-then-else with different compiler calls, but the name of the called compiler is modified to meet the requirements of host and target compilers.

===== Appropriate OpenDirectory Directory Pages =====
  *[[http://www.dmoz.org/Computers/Software/Operating_Systems/Linux/|OpenDirectory "Top: Computers: Software: Operating Systems: Linux"]].
    *[[http://www.dmoz.org/Computers/Software/Operating_Systems/Linux/Embedded/|OpenDirectory "Top: Computers: Software: Operating Systems: Linux: Embedded"]].
    *[[http://www.dmoz.org/Computers/Software/Operating_Systems/Linux/Platforms/|OpenDirectory "Top: Computers: Software: Operating Systems: Linux: Platforms"]].
  *[[http://www.dmoz.org/Computers/Software/Operating_Systems/Embedded/|OpenDirectory "Top: Computers: Software: Operating Systems: Embedded"]].
  *[[http://www.dmoz.org/Computers/Software/Operating_Systems/Realtime/|OpenDirectory "Top: Computers: Software: Operating Systems: Realtime"]].
    *[[http://www.dmoz.org/Computers/Software/Operating_Systems/Realtime/Open_Source/|OpenDirectory "Top: Computers: Software: Operating Systems: Realtime: Open Source"]].
    *[[http://www.dmoz.org/Computers/Software/Operating_Systems/Realtime/Linux/|OpenDirectory "Top: Computers: Software: Operating Systems: Realtime: Linux"]].
{{tag>Linux}}
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