Hi,
I am using devkit8000.
I can't able to open /sys/class/gpio/export from C code.
I can use the Terminal Emulator and see the /sys/class/gpio/export.
Can someone tell me what I am doing wrong?
Here is my soruce code
fd = open("/sys/class/gpio/export", O_WRONLY);
if (fd < 0)
{
printf("Cannot open GPIO export \n");
exit(1);
}
Thanks!
Dennis
Hi,
I am using devkit8000.
I can't able to open /sys/class/gpio/export from C code.
I can use the Terminal Emulator and see the /sys/class/gpio/export.Can someone tell me what I am doing wrong?
Here is my soruce code
fd = open("/sys/class/gpio/export", O_WRONLY);
if (fd < 0)
{
printf("Cannot open GPIO export \n");
Well, one of the things you are doing wrong is that you do not print
errno (or use perror() )
that way you get the error code from open
when you have that, look at man 2 open on a linux system to find info
on the possible causes.
Have fun
Frans
What are the permissions on /sys/class/gpio/export ? You may have to change them with “sudo chmod u+rwx” so you can read/write to them as a normal user.
Hope this helps.
– @
Thanks for your reply!
I captured some messages after # adb shell.
# cd /sys/class/gpio
# ls -l
--w------- root root 4096 2010-08-12 15:17 export
--w------- root root 4096 2010-08-12 15:17 unexport
lrwxrwxrwx root root 2010-08-12 15:17 gpiochip0 -
../../devices/virtual/gpio/gpiochip0
lrwxrwxrwx root root 2010-08-12 15:17 gpiochip32 -
../../devices/virtual/gpio/gpiochip32
lrwxrwxrwx root root 2010-08-12 15:17 gpiochip64 -
../../devices/virtual/gpio/gpiochip64
lrwxrwxrwx root root 2010-08-12 15:17 gpiochip96 -
../../devices/virtual/gpio/gpiochip96
lrwxrwxrwx root root 2010-08-12 15:17 gpiochip128 -
../../devices/virtual/gpio/gpiochip128
lrwxrwxrwx root root 2010-08-12 15:17 gpiochip160 -
../../devices/virtual/gpio/gpiochip160
lrwxrwxrwx root root 2010-08-12 15:17 gpiochip192 -
../../devices/platform/i2c_omap.1/i2c-1/1-0049/twl4030_gpio/gpio/
gpiochip192
The export file is root permission after boot system, I can not write
it in my libLedControl.so.
if I did chmod command as follows, then I can write data into export.
# chmod 0666 export
# ls -l
-rw-rw-rw- root root 4096 2010-08-12 15:17 export
--w------- root root 4096 2010-08-12 15:17 unexport
lrwxrwxrwx root root 2010-08-12 15:17 gpiochip0 -
../../devices/virtual/gpio/gpiochip0
lrwxrwxrwx root root 2010-08-12 15:17 gpiochip32 -
../../devices/virtual/gpio/gpiochip32
lrwxrwxrwx root root 2010-08-12 15:17 gpiochip64 -
../../devices/virtual/gpio/gpiochip64
lrwxrwxrwx root root 2010-08-12 15:17 gpiochip96 -
../../devices/virtual/gpio/gpiochip96
lrwxrwxrwx root root 2010-08-12 15:17 gpiochip128 -
../../devices/virtual/gpio/gpiochip128
lrwxrwxrwx root root 2010-08-12 15:17 gpiochip160 -
../../devices/virtual/gpio/gpiochip160
lrwxrwxrwx root root 2010-08-12 15:17 gpiochip192 -
../../devices/platform/i2c_omap.1/i2c-1/1-0049/twl4030_gpio/gpio/
gpiochip192
The following is libLedControl.so permission, does it relate to issue?
# cd /system/lib
# ls -l
-rwxr-xr-x system system 1598036 2010-08-03 10:11 libicudata.so
-rwxr-xr-x system system 5084 2010-08-03 10:11 libreference-
cdma-sms.so
-rw-r--r-- system system 153128 2010-08-03 10:11 libRS.so
-rw-r--r-- system system 814944 2010-08-03 10:11
libopencore_common.so
-rwxr-xr-x system system 9376 2010-08-03 10:11 libpagemap.so
-rwxr-xr-x system system 450660 2010-08-03 10:11
libopencore_net_support.so
-rw-r--r-- system system 332448 2010-08-03 10:11
libopencore_author.so
-rw-r--r-- system system 731844 2010-08-03 10:11 libicui18n.so
-rw-r--r-- system system 5272 2010-08-03 10:11 libstdc++.so
-rwxrwxrwx root root 5228 2010-08-12 15:27
libLedControl.so
-rwxr-xr-x system system 568896 2010-08-03 10:11 libasound.so
-rw-r--r-- system system 9220 2010-08-03 10:11 libdl.so
-rwxr-xr-x system system 9648 2010-08-03 10:11 libemoji.so
-rwxr-xr-x system system 18604 2010-08-03 10:11
libopencore_mp4localreg.so
-rwxr-xr-x system system 138716 2010-08-03 10:11
libomx_sharedlibrary.so
-rwxr-xr-x system system 5236 2010-08-03 10:11 pthres.so
Can anyone help me how to make it works?
Thanks!
Dennis