Difference between revisions of "GPIOlib"
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(LED -> SWITCH) |
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| Line 58: | Line 58: | ||
* Define envt variable (for portability): | * Define envt variable (for portability): | ||
<pre class="apf"> | <pre class="apf"> | ||
| − | # export | + | # export SWITCH=175 (APF27Dev) |
or | or | ||
| − | # export | + | # export SWITCH=3 (APF51Dev) |
</pre> | </pre> | ||
* Ask kernel to export the GPIO: | * Ask kernel to export the GPIO: | ||
<pre class="apf"> | <pre class="apf"> | ||
| − | # echo $ | + | # echo $SWITCH > /sys/class/gpio/export |
</pre> | </pre> | ||
* Access functions are created: | * Access functions are created: | ||
<pre class="apf"> | <pre class="apf"> | ||
| − | # ls /sys/class/gpio/gpio$ | + | # ls /sys/class/gpio/gpio$SWITCH/ |
active_low edge subsystem value | active_low edge subsystem value | ||
direction power uevent | direction power uevent | ||
| Line 74: | Line 74: | ||
* Check GPIO direction and put in output: | * Check GPIO direction and put in output: | ||
<pre class="apf"> | <pre class="apf"> | ||
| − | # cat /sys/class/gpio/gpio$ | + | # cat /sys/class/gpio/gpio$SWITCH/direction |
in | in | ||
</pre> | </pre> | ||
* Get switch status: | * Get switch status: | ||
<pre class="apf"> | <pre class="apf"> | ||
| − | # cat /sys/class/gpio/gpio$ | + | # cat /sys/class/gpio/gpio$SWITCH/value |
1 (released) | 1 (released) | ||
... | ... | ||
| − | # cat /sys/class/gpio/gpio$ | + | # cat /sys/class/gpio/gpio$SWITCH/value |
0 (pressed) | 0 (pressed) | ||
</pre> | </pre> | ||
Revision as of 13:39, 24 May 2011
With recent Linux kernel (> 2.6.3x), there is an abstraction layer meant to ease GPIO usage: gpiolib. We will explain here how to use it.
Contents
Installation
- If not already done:
$ make linux26-menuconfig
Device Drivers --->
-*- GPIO Support --->
[*] /sys/class/gpio/... (sysfs interface)
$ make
- reflash your kernel (if needed)
Usage
Blink APFxxDev i.MX LED
- Find the GPIO number connected to the LED, eg:
- for APF27Dev: PF14 -> PortF (n°6) pin 14 -> (6-1)*32 + 14 -> GPIO n°174
- for APF51Dev: GPIO1_2 -> Port 1 pin 2 -> GPIO n° 2
- Define envt variable (for portability):
# export LED=174 (APF27Dev) or # export LED=2 (APF51Dev)
- Ask kernel to export the GPIO:
# echo $LED > /sys/class/gpio/export
- Access functions are created:
# ls /sys/class/gpio/gpio$LED/ active_low edge subsystem value direction power uevent
- Check GPIO direction and put in output:
# cat /sys/class/gpio/gpio$LED/direction in # echo out > /sys/class/gpio/gpio$LED/direction # cat /sys/class/gpio/gpio$LED/direction out
- Play with GPIO value to blink LED:
# echo 1 > /sys/class/gpio/gpio$LED/value # echo 0 > /sys/class/gpio/gpio$LED/value
Get APFxxDev i.MX switch status
- Find the GPIO number connected to the switch, eg:
- for APF27Dev: PF15 -> PortF (n°6) pin 15 -> (6-1)*32 + 15 -> GPIO n°175
- for APF51Dev: GPIO1_3 -> Port 1 pin 3 -> GPIO n°3 ((1-1)*32 + 3)
- Define envt variable (for portability):
# export SWITCH=175 (APF27Dev) or # export SWITCH=3 (APF51Dev)
- Ask kernel to export the GPIO:
# echo $SWITCH > /sys/class/gpio/export
- Access functions are created:
# ls /sys/class/gpio/gpio$SWITCH/ active_low edge subsystem value direction power uevent
- Check GPIO direction and put in output:
# cat /sys/class/gpio/gpio$SWITCH/direction in
- Get switch status:
# cat /sys/class/gpio/gpio$SWITCH/value 1 (released) ... # cat /sys/class/gpio/gpio$SWITCH/value 0 (pressed)
