GPIO Sysfs is the standard way to manage the GPIO lines under Linux from user space. It uses the directory /sys/class/gpio to set or read any GPIO line.
Inside this directory there are two directories called:
To manage a GPIO line you have to know its kernel ID. The Kernel IDs of any Acme Systems SoM are available on:
The Atmel chips have the GPIO lines organized by 32 bit port called PA,PB, etc.
Before set or read a port you have to export it. Follow an example on how to set, reset and read the port PA1 (Kernel ID 1) from the command line:
Set the line status of GPIO line PA1
# echo 1 > /sys/class/gpio/export # echo out > /sys/class/gpio/pioA1/direction # echo 1 > /sys/class/gpio/pioA1/value
Reset the line status of GPIO line PA1
# echo 0 > /sys/class/gpio/pioA1/value
Read the line status of GPIO line PA1
# echo in > /sys/class/gpio/pioA1/direction # cat /sys/class/gpio/pioA1/value
The official documentation about the GPIO Sysfs interface is available on:
A simple module called acmepins is available on GitHub to manage the GPIO lines using the sysfs method.
As shown in the following examples with this module is possible to manage the GPIO states using directly the board pin names or the Atmel chip pin names or the GPIO Kernel IDs.
This example will blink a led wired to a output line
from acmepins import GPIO from time import sleep #FOX Board G20 example led = GPIO('J7.3','OUTPUT') #Aria G25 example #led = GPIO('W9','OUTPUT') #Arietta G25 example #led = GPIO('J4.29','OUTPUT') #Acqua A5 example #led = GPIO('J3.32','OUTPUT') while True: led.on() sleep(1) led.off() sleep(1)
there are two ways o read a GPIO input state:
from acmepins import GPIO from time import sleep #FOX Board G20 example Button=GPIO('J7.5','INPUT') #Aria G25 example #Button=GPIO('W15','INPUT') #Arietta G25 example #Button=GPIO('J4.28','INPUT') #Acqua A5 example #Button=GPIO('J3.33','INPUT') i=0 while True: sleep(1) i+=1 print i if Button.digitalRead()==0: print "Pressed" while Button.digitalRead()==0: pass
from acmepins import GPIO from time import sleep def event_handler(): print "Input changed" #FOX Board G20 example Button=GPIO('J7.5','INPUT') #Aria G25 example #Button=GPIO('W15','INPUT') #Arietta G25 example #Button=GPIO('J4.28','INPUT') #Acqua A5 example #Button=GPIO('J3.33','INPUT') Button.set_edge("both",event_handler) i=0 while True: print i i=i+1 sleep(0.5)
One of three conditions can be checked:
gpiolib.c is a simple library to manage the gpio via sysfs in C.
#define GPIO_IN 1 #define GPIO_OUT 0 gpioexport(80); gpiosetdir(80,GPIO_OUT); for (;;) { gpiosetbits(80); gpioclearbits(80); }
#define GPIO_IN 1 #define GPIO_OUT 0 gpioexport(80); for (;;) { printf("%d\n",gpiogetbits(84)); }
The gpiolib.c library is available on Github.
An in-deep explanation on how the GPIO lines work and how to manage them faster is available on:
This is a small group of Linux utilities for the Atmel AT91SAM9G25 and AT91SAM9G20 microcontroller units (MCUs). The utilities target The Aria G25 and the FoxG20 boards from Acme Systems and will most likely work on other boards based on the same MCUs. Some of the utilities have the same names as those from the earlier FoxLX board from Acme System; that board was based on the Etrax LX processor from Axis communications.
These utilities mainly work with individual GPIO lines and may be extended to other protocols that can be implemented by "bit banging" GPIO lines. These include I2C (a.k.a. TWI), "one wire" (known as "w1" by the Linux kernel) from Dallas Semiconductor (now Maxim), and the two wire protocol for the SHT-71 .
Download on your board the latest utilities version from the D.Gilbert web server
~# wget http://sg.danny.cz/foxg20/ag25g20_utils-0.97r14.tgz
Uncompress the .tgz file
~# tar xvzf ag25g20_utils-0.97r14.tgz
Compile and install them
~# cd ag25g20_utils-0.97r14 ~/ag25g20_utils-0.97r14# make ~/ag25g20_utils-0.97r14# make install
Refer to the original README file to learn how to use these utilities
Following is a list of quick examples:
~# g25gpio_status -h
~# g25gpio_status -a -p A PA0: PIO status: 0 (peripheral ACTIVE) PIO output status: 0 (line pure input) input filter status: 0 (glitch filter DISabled) output data status: 0 pin data status: 0 interrupt mask: 0 (DISabled) multi driver status: 0 (pin driven high and low) pad pull-up status: 0 (ENabled) peripheral A function [sr1:0, sr2:0] input filter slow clock status: 0 (master-fast) pad pull down status: 1 (DISabled) additional interrupt modes mask: 0 (Both edges) edge/level status: 0 (edge detection) fall/rise - low/high status: 0 (falling edge or low level detection) locked status: 0 (not locked) write protect mode: WPEN: 0 (DISabled) schmitt trigger status: 0 (ENabled ) IO drive: 0 (HI_DRIVE) ...
of course it is possible to read all the other ports
~# g25gpio_status -a -p B ~# g25gpio_status -a -p C
~# g25gpio_set -h
~# g25gpio_set -p B -b 11 -u ~# g25gpio_set -p B -b 12 -u ~# g25gpio_set -p B -b 13 -u ~# g25gpio_set -p B -b 14 -u
Related links