Nfyku: Created page with '== notes == Sysfs exports information about devices and drivers from the kernel device model to userspace. Gpio-sysfs is the prefered method for accessing gpio from userspace. It…'

2011-06-22T12:59:54Z

Created page with '== notes == Sysfs exports information about devices and drivers from the kernel device model to userspace. Gpio-sysfs is the prefered method for accessing gpio from userspace. It…'

New page

== notes ==
Sysfs exports information about devices and drivers from the kernel device model to userspace.
Gpio-sysfs is the prefered method for accessing gpio from userspace. It deals with one pin at a time and works in means of reading and writing to files for control.

The control files for each gpio chip is contained within '/sys/class/gpio/'
~ # ls /sys/class/gpio/
export gpiochip231 gpiochip235 gpiochip240 gpiochip248 unexport
To begin with there is only two files 'export' and 'unexport' and a folder for each gpio, each gpio has an ID number.

In each folder there are files that contains information about the chip:
~ # ls /sys/class/gpio/gpiochip231/
base label ngpio subsystem uevent
*'base' contains the ID of the chip, i.e. for gpiochip231, the ID is 231
~ # cat /sys/class/gpio/gpiochip231/base
231
*'label' contains the address (so that you are able to identify which gpio you are dealing with)
~ # cat /sys/class/gpio/gpiochip231/label
/plb@0/gpio@81400000
*'ngpio' contains the number of gpio pins available

In order to get access to a GPIO pin it is necessary to export it using the export file:
echo NN > /sys/class/gpio/export
Where NN is the base of the GPIO chip plus the pin number, i.e. for pin0 of gpiochip231 NN=231, for pin1 NN=232, etc.

An example:
echo 231 > /sys/class/gpio/export
echo 232 > /sys/class/gpio/export
This gives access to pin0 and pin1.

When a pin is exported, a folder is created: '/sys/class/gpio/gpioNN'. Within such a folder you have the control files for the pin, 'direction' and 'value'
~ # ls /sys/class/gpio/gpio231/
direction subsystem uevent value

Example, setting direction of pin0 as output:
echo out > /sys/class/gpio/gpio231/direction
Possible commands for direction:
high Set GPIO to an output with a starting value of 1
low Set GPIO to an output with a starting value of 0
out Same as low
in Set GPIO to an input

Example, setting value of a pin0 to 1, then reading the value:
echo 1 > /sys/class/gpio/gpio231/value
cat /sys/class/gpio/gpio231/value
1

Current design:
sig phys NN
TDI -> pin6 -> 231
TMS -> pin4 -> 232
TDO -> pin3 -> 233
TCK -> pin1 -> 234

== References ==

*[http://www.labbookpages.co.uk/electronics/avrs/toolChain.html AVR Hex to SVF]
*[http://dangerousprototypes.com/tag/xsvf-player/ XSVF stuff to look in to]
*[http://dangerousprototypes.com/docs/Bus_Pirate Bus pirate]
*[http://code.google.com/p/the-bus-pirate/updates/list some bus pirate files]
*[http://code.google.com/p/the-bus-pirate/downloads/detail?name=BPv3.XSVFplayer.v1.1.zip Bus pirate xvsf player stuff]
*[http://www2.embedded-projects.net/index.php?page_id=221 Even some more about xsvf]
*[http://www.avrfreaks.net/index.php?name=PNphpBB2&file=viewtopic&t=57510&highlight=spi+ngw100]
*[https://docs.blackfin.uclinux.org/doku.php?id=linux-kernel:drivers:simple-gpio]
*[http://www.avrfreaks.net/wiki/index.php/Documentation:Linux/GPIO]
*[http://xilinx.eefocus.com/wall/index.php?act=read&id=1605]
*[http://hackaday.com/2008/12/01/bus-pirate-firmware-update-v0c-jtag-and-more/]
*[http://www.avrfreaks.net/wiki/index.php/Documentation:NGW/Newbie/Detailed_IO_Tutorial]

[[Category:Embedded]]

JTAG - Revision history

Nfyku: Created page with '== notes == Sysfs exports information about devices and drivers from the kernel device model to userspace. Gpio-sysfs is the prefered method for accessing gpio from userspace. It…'