Table of Contents
[hemmerling] Linux 8/12 - Embedded Systems with Linux
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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 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 Lemonboard with Ubuntu Linux / Linux, show Gpio Pins:
cat /sys/kernel/debug/gpio
- Set Gpioi LED Value:
echo "1" > /sys/class/gpio/gpio203/value echo "0" > /sys/class/gpio/gpio2/value
- Additionally, there is a small application “gpioin”. Config the GPIO CSI0_DAT12 to INPUT:
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
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.
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