[OpenWrt-Devel] How to config GPIO and read the GPIO value in OpenWRT

[Hartmut Knaack]

Afkar Rafique schrieb am 16.10.2015 um 03:47:
> Thanks for the reply.
> 
> I have change the script as below:
> 
> #!/bin/sh /etc/rc.common
> 
> START=19
> start() {       
>         echo in > /sys/class/gpio/gpio16/direction 2> /dev/null       
>         echo 16 > /sys/class/gpio/export 2> /dev/null

Still, you can only set the direction AFTER exporting the GPIO (otherwise the gpioXX
directory with its contents like direction don't exist).

>         if [ "$(cat /sys/class/gpio/gpio16/value)" == "1" ] ; then
>             echo "255" > /sys/devices/platform/leds-gpio/leds/db120:green:status/brightness     
>         else
>             echo "0" > /sys/devices/platform/leds-gpio/leds/db120:green:status/brightness     
>         fi
> }
> 
> I need to monitor the LED on/off all the time during runtime.
> 
> During start of this script its working, but not getting how to make it work run time.
> 
> Could you please explain how i can do it in gpio-button.

That would require you to add a custom button definition in the mach-file of your
specific device and compile your own firmware image.
You could however use a small script which infinitely loops through your poll and sleeps
for a second, so the CPU can work on other tasks, too (while true; do if...then...else
sleep 1; done). Downside is, that you can only react to "button press events", which are
long enough (one second, as this is the low limit of sleep time). Also, don't forget to
let it run in background, so you don't block your init process.

> 
> On Fri, Oct 16, 2015 at 3:38 AM, Hartmut Knaack <knaack.h at gmx.de <mailto:knaack.h at gmx.de>> wrote:
> 
>     Afkar Rafique schrieb am 15.10.2015 um 04:07:
>     > Thanks for the reply.
>     >
>     > i have Create /etc/init.d/buttons and written below script:
>     >
>     > #!/bin/sh /etc/rc.common
>     > START=19
>     > start() {
>     >         /bin/umount /etc/config 2>/dev/null
>     >         echo out > /sys/class/gpio/gpio16/direction 2> /dev/null
>     >         echo 16 > /sys/class/gpio/export 2> /dev/null
>     >         if [ "$(cat /sys/class/gpio/gpio16/value)" == "1" ] ; then
>     >             echo "255" > /sys/devices/platform/leds-gpio/leds/db120:green:status/brightness
>     >         else
>     >             echo "0" > /sys/devices/platform/leds-gpio/leds/db120:green:status/brightness
>     >         fi
>     > }
>     >
>     > and restart .
>     >
>     > chmod +x /etc/init.d/buttons
>     > /etc/init.d/buttons enable
>     > /etc/init.d/buttons start
>     >
>     > Now i am able to read the GPIO 16 value 1/0 based on GPIO state, but as above script i have written to ON/OFF the Status LED based on GPIO value, Status LED is not getting OFF even if GPIO16 value is "0".
>     >
>     > Can anyone please help on this
>     >
> 
>     Quite a mess you've got there. No idea why you need to umount /etc/config,
>     but anyway: First thing in GPIO setup is exporting, then you set its direction.
>     If you intend to read the GPIO status, then better use "in" as direction.
>     Now, do you just want to do an action (LED on/off) just during start of this
>     script, or all the time during runtime, when the GPIO status changes? In the
>     latter case, you should look into gpio-button.
> 
>     >
>     >
>     > On Thu, Oct 15, 2015 at 12:37 AM, Martin Blumenstingl <martin.blumenstingl at googlemail.com <mailto:martin.blumenstingl at googlemail.com> <mailto:martin.blumenstingl at googlemail.com <mailto:martin.blumenstingl at googlemail.com>>> wrote:
>     >
>     >     On Wed, Oct 14, 2015 at 12:19 PM, Afkar Rafique <afkar.ec at gmail.com <mailto:afkar.ec at gmail.com> <mailto:afkar.ec at gmail.com <mailto:afkar.ec at gmail.com>>> wrote:
>     >     > Could anyone please explain how i can configure and read GPIO value.
>     >     There's an article on the wiki which explains how to set a GPIO to a
>     >     specific value: [0]
>     >     If you want to read a GPIO value then you use direction "in" and then
>     >     simply cat to read the "value".
>     >
>     >     The only thing that you might have to do is doing a bit of maths to
>     >     get the correct GPIO number.
>     >     When you are trying to read GPIO #16 then it's GPIO #16 of a specific
>     >     chip -> /sys/class/gpio/ should contain a file gpiochipNNN.
>     >     What you do is take NNN (let's assume it's 456) and add your GPIO
>     >     number to it: 456 + 16 = 472 -> this is the number needef to "export"
>     >     the GPIO.
>     >
>     >
>     >     [0] http://wiki.openwrt.org/doc/hardware/port.gpio#software
>     >
>     >
>     >
>     >
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> 
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