GPIO under Android

Dave McLaughlin
Hi all, I am familiar with programmed embedded systems with the likes of
UCOS and no OS etc and this is my first time to learn to build Android on a
mini6410 of which I am enjoying the experience.

The thing I am stuck at is lack of documentation and unfamiliar with Linux
etc. (Again a new learning experience as I am now running Ubuntu 64 to
build the Android 2.3.4 system)

I have a custom designed board that the mini6410 plugs into. This includes
a AC-DC power supply, a DC-DC power supply and external RS232 drivers and
external connection point for the WiFi board.

Here are some images of the board and enclosure.

On this PPCB design I have a push button power supply controller and this
has 2 connections that go to the GPIO pins on the mini6410. One is for an
interrupt ouput that goes low when the button is pressed. The second is an
input to the push button controller that allows the system to kill the
power. When this is pulled low by the mini6410 the power is switched off.
This would normally be when all processes are either shutdown or put to
sleep and data saved. This is why there is an input to signal the processor
power should be removed.

The issue I have is where I handle these GPIO input and outputs. I think
looking at the code this should be done in the Linux kernel. It needs to
alert the Android OS though that power is being switched off and allow any
running application to do housework before the power is removed. I am stuck
right now with lack of knowledge on the correct place for this code and
looking for some pointers.

This is a home project to allow me to interface to my electrical meter to
monitor the power usage and control heating and air-conditioning in my

Appreciate any help anyone can offer, even if just where to look in the
code and if possible a place to look for sample as I can figure out what I
need from there.


Hi Dave have you read this documentation?
also where did you found the information to build Android 2.3.4?

Dave McLaughlin
Hi Andre,

Thanks for the info. I'll have a read of it this week.

I got the download from the FTP site. Look for these files:


They were dated Nov 2011 so I assumed an update. When I downloaded I found
2.3.4 on there. :)


Dave McLaughlin
Oops. Wrong files.

Try these


Oct release it should be, not Nov.



Thanks Dave, which FTP site?, can you post the address?

never mind I found it :),

Martin Beuttenmüller
Hi Dave,
i've just stumbled over your pictures. What I can see so far is
a nice and tidy job: very well done.

Just a small hint: in the 2'nd picture at the middle/top there is
a flat-ribbon going thru the PCB. Perhaps you can add some protection
to the edge of the PCB to avoid damages of the ribbon.

As I say'd before: seldom seen such a tidy selfmade gadget !!!

Martin ...

Hi there,
Dave, did you manage to access GPIO on Android ?

I worked a bit to get serial ports working, and finally I have a working
service class to handle serial port com.
But the settings of the COM are applied by the pre-compiled library (are the source file available ?)

Is access to GPIO mean recompile the kernel and add things like gpio-sysfs,
and write a driver accessible with JNI ? If so, I seriously need help ;o)

It is a shame that we cannot see what is behind setLedState() of the

Anyway thanks a lot,

Dave McLaughlin
Hi Martin and Muth,

I just stumbled across your replies. I with this forum would do email

Martin, the ribbon at the top of the pic part of the LCD supplied by
FriendlyArm so I have no control over this. Thanks for the kind comments.
Much appreciated. (As it happens this box is now going to be used for a
customer test project)

Muth, working on GPIO now. I just got I2C to work tonight (there is a
posting about this on the forum). I already have RS232 from elsewhere. The
FriendlyArm library is far too limited in the calls it provides. I can't
see why they would make this source closed when so many people with their
boards would like to see the code and my development time would have been
reduced from months to weeks. I am designing in the Mini210 for my next
commercial project so it would pay them to do so. Mindee, do you have a
comment on this, if you're reading this.

Anyway, I am slowly learning to use the JNI and looking to add GPIO next.
I'll let you know how I get on.


Hi Dave !

A huge thanks, I didn't expect a reply, it's really kind.

Really interesting, I have an i2c BMP085 digital barometer I will test it !

I'll follow your dev with lot of interest, again, thanks a lot for sharing
Dave !

Dave McLaughlin
Hi Muth, how did you get on with the I2C?

Did it work for you?

I am still trying to get GPIO working. I don't need any kernal code, just a
way for Android to set GPIO pins.


Harsha Herur

I have got GPIO working on Tiny6410.

I had to compile the kernel to include /sys/class/gpio. This exposes the
gpio pins for root.

I then compiled android system making changes to init.rc. Added permissions
to gpio export in init.rc as below:
chown system system /sys/class/gpio/export
chmod 0666  /sys/class/gpio/export

Later added the pin numbers to export in init.rc. The pin numbers can be
found from /sys/class/gpio/gpiochip104/base(similarly for other pins)
write /sys/class/gpio/export 108 (similarly for other pins)

This gives access to individual pins through gpio108/direction and
gpio108/value. But these are again write protected so i have changed
permissions in init.rc
chown system system /sys/class/gpio/gpio108/direction
chown system system /sys/class/gpio/gpio108/value
chmod 0666 /sys/class/gpio/gpio108/direction
chmod 0666 /sys/class/gpio/gpio108/value (similarly for other pins)

This should make it work.

For controlling through a program I have used jni:
fp = fopen("/sys/class/gpio/gpio108/value", "rb+"));
fwrite(&set_value, sizeof(char), 1, fp);
It is also possible using a simple file operation in java.


Dave McLaughlin
Excellent work Harsha.

Once I get my Ubuntu system working again (update to 12.04 has trashed the
bootup) I'll complete my JNI for I2C and GPIO and update the source so
others can get it. I'll comment your help in the code.

Much appreciated for your time.

PS... I will shortly test this on the Mini210 too as I am moving to that
instead of the Mini6410 because of the fast speed and better LCD and touch.

Harsha Herur
Hi Dave,

Great that you are publishing the source. It took me almost a week to get
GPIO working. I would be glad to help if anything further is required.
email -


Dave McLaughlin
Cheers Harsha,

In case you missed it, my I2C code is here. I'll update this with GPIO next
based on your help and code.


Dave McLaughlin
Hey Harsha. 

I finally got time this weekend with the wife being away to put in some
time to get GPIO working and after many hours today I have it working on
the Mini210. Now that I know how to do it, I will do the same for the

Took me a little while to figure it out and work out how it all works but I
am learning more each day and enjoying the challenge. Your help put me in
the right direction.

I added all the changes to init.rc and now all the GPIO that is available
on the GPIO connector is included when I install Android on the flash.

For now I have the GPIO working tested with ADB and I am going to update
the source for the JNI once I have that working.


olli pyynönen
Hi everybody! My intention is to connect two i/o-cards (IOIO V1/,2, 48-line
i/o) via I2C GPIO expander, can you suggest the easiest (or cheapest) way
to do it with Android (2.3<)?

Great job Dave,
When will your wife be away again so that your can share your Mini210 GPIO
code with us
Thank you in advance

Dave McLaughlin
Hi Mexx.

I have done the coding and tested it on my Mini210 so I will try and get it
up this weekend or at least over the next few days.


thank you in advance

Dear Friends
last two days I am trying to establish RS232 communication in Android with
my Tyni6410 development board.I am using libfriendlyarm-hardware
library,success in sending data from board to PC ( write() function) but
there is no effect with read() fuction.I am testing serial communication
with Terminal emulator in windows 7 ( board connected to laptop usb port
via usb-serial converter ). what is wrong with read() function ?
thanks in advance

Hi,I would like to know how access any GPIO in Java (MINI6410)? I use the, but there are small quantity GPIO's (led's,
ADC, Memory I2C, PWM). I want to use, for example, the pushbutton. I want
to use others I2C devices (because in i can't to
put a address slave). I want to use others GPIO's (extension). How i
generate a Thanks.

Dave McLaughlin
Hi Anderson,

I am trying to create a new SourceForge entry for the GPIO software. I will
post a link here once it is up. It is not 100% completed and tested yet but
I would welcome any others to help with it. I am so busy with a work
project that I don't get much time on it just now.

Give me a couple of days and it will be up and ready for download.


Dave McLaughlin
Hi Mexx and all,

I finally put it up on sourceforge but I am still waiting for the PCB to
arrive to test this with my Mini210 but initial testing works.

This includes GPIO and I2C. 

Right now, all that is up there is the JNI code. I'll upload the Android
Java this week.


Hi Dave,
Thank you for sharing your code, I will test in in next few weeks and
Really appreciate your effort...

Dave McLaughlin
Hi Danijel,

I changed the files I uploaded. I included the JAVA file and removed the
old files.


Hello guys

Thanks for the useful thread.

I have a question:

Is it possible to configure the GPIO permissions in Android Java code
instead of rebuilding Android system with a modified init.rc ? has anyone
done it successfully ?

Is there any chance Dave that you can email it me, unfortunately
sourceforge is not accessable from here. (real real pain) 
phil_in_china at yahoo dot com

      Nice work you had done Mr.Dave

  I'm working with ANDROID ICS in Beaglebone. I need to implement just 4
GPIO buttons like your device MENU,BACK,HOME and POWER ON/OFF. In my
beaglebone following GPIO pins are available in header GPIO0_26,GPIO1_1,
GPIO1_2, GPIO1_3, GPIO1_4, GPIO2_1, GPIO2_8 other some pins are available i
think that its enough to explain my problem. 

  I need to know how to configure the GPIO buttons in kernel and how to map
the key according to ANDROID key code, more than week i'm trying this but i
cant succeed.

  Can any one help me to finish this.Especially i want to know which files
have to be modify in ANDROID AOSP.
Any one have handled it plz mail me (
i dono that if any one reply for this post it will come to my mail or not
thats why i'm enclosing my mail id)

  I'm very thankful, who make me clear

  Thanks in advance.

Dave McLaughlin

Why not download the source code for the Mini6410 or Mini210 and see how
FriendlyArm did it? You can get them from the FTP site.

Thanks for your reply Mr.Dave

       Sorry Mr.Dave I'm using TI-Android-ICS source code. My works are
almost over (schematic,BOM,etc.) with the reference of AM335xEVM and
Beaglebone  Schematic.So at the last moment i can't change it to new
things.But I've plan to design another android device with in 1 month for
automation purpose so mini6410 or mini210 will help me rather than TI
image.Mean while i'll get the source code and go through it. I hope
mini6410 help me to complete my upcoming device.

      Now i need to implement the buttons in my device.Can yo tell me the
procedure for configure the GPIO for ANDROID menu button.

     I hope you will help me.

Thanks in advance..!!

Mr.dave Chains is my nick name..Sangilikumar is my original name  sorry for
the confusion..!!

Dave McLaughlin
Hi all. Been a while.

I got GPIO working now on my Mini210 but I can't get GPH0_0 to change
state. It remains HIGH no matter what I do. I suspect a fault with the
board and will confirm with my other board in the next few days.

I'll be updating the files on sourceforge in the next day or so once I have
finished tidying it up.

Thanks to all for your help. It has been fun learning how this all works
and how JNI works too.


Thank you for the effort...

hey hi
can anyone guide me how get gpio,leds,adc pins...
i cannt found the pins in tiny6410..
i hve install android...
hve got all the setup JNI n all but the path for acessin the pins cannt  b
if nyone knw how to do??
harsha has xplained but m new to it m not able to get wherre to write dat
commmnds n all..
i really need help 
thnks in advance

Hi Dave, 
I read your post and downloaded the code, a great work, I am new to Android
and Java, I could not understand how to use your project files. I created a
new tiny210 android project and included your project files, now how can I
use them ?
I also have following problems:

1. JNIEXPORT in axonio.c shows syntax error.

2. setdirectionGPIO(String nodeName, int State);
what should I write in place of nodeName to access GPH0_0 of tiny210.

Any help can be really appreciated, thanks in advance.

I have the same doubts as asci. How do you use the setdirectionGPIO, what
to write in the place of nodeName.

Any help would be really appreciated.

Dave McLaughlin
In my test code I have this

setdirectionGPIO("gpio128", 1);

gpio128 is the device name. You'll need to locate this in your kernel

Phuc tran
Hi Dave,
Thank you for sharing your code,
I downloaded your code on page 
but i can't look for lib
I hope you will help me.