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Hi Ram,

1.) Please provide the user usage information of GPIO driver, on  Linux-2.6.33.

Go through kernel documentation "Documentation/gpio.txt" for more details

2.) How to access GPIO pin on user side like gpio_request();  gpio_request_input(); etc

http://processors.wiki.ti.com/index.php/Sitara_GPIO_Driver_User_Guide#Driver_Usage

Regards

AnilKumar

Noticed in your other forum threads that you have some confustion between the kernel and user space interfaces to GPIOS. User space access to the sysfs GPIO driver is all through files. Here's an example to toggling GPIO 11 in a Linux console or terminal:

cd /sys/class/gpio/
echo 11 > export
cd gpio11
echo out > direction
echo 0 > value
echo 1 > value
echo 0 > value

The equivalent code in C is:

#include <fcntl.h>       /* For open() */

#include <unistd.h>      /* For read(), close() */


int main(int argc, char *argv[])
{
 int fd;
 fd = open("/sys/class/gpio/export", O_WRONLY);
 write(fd, "11", 3); // Include null!
 close(fd);

 fd = open("/sys/class/gpio/gpio11/direction", O_WRONLY);
 write(fd, "out", 4);
 close(fd);

 fd = open("/sys/class/gpio/gpio11/value", O_WRONLY);
 write(fd, "0", 2);
 write(fd, "1", 2);
 write(fd, "0", 2);
 close(fd);

 return(0);
}

Please take note that you must check that the GPIO line you want to use is pinmux'ed to an external pin. That involves looking at the kernel code and possibly modifiying the kernel.

Hi,

Thanks for your above example to toggle gpio....

Hi, if I want set  GP2[3] to out direction .And set it to 1 or 0, how can I use the function write and open?\

 fd = open("/sys/class/gpio/export", O_WRONLY);
 write(fd, "??", ??); // Include null!
 close(fd);

 fd = open("/sys/class/gpio/gpio11/direction", O_WRONLY);
 write(fd, "??", ？？);
 close(fd);

fd = open("/sys/class/gpio/gpio11/value", O_WRONLY);
 write(fd, "0", ？？);

Hi,

write(fd, buf, len);

fd - file pointer

buf - contains characters ex: "1" or "0" or "in" or "out"

len - length of the buffer ex: 2 or 2 or 3 or 4.

Regards

AnilKumar

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Hi,  

cd /sys/class/gpio/
echo 11 > export
cd gpio11
echo out > direction
echo 0 > value
echo 1 > value
echo 0 > value

The equivalent code in C is:

#include <fcntl.h>       /* For open() */

#include <unistd.h>      /* For read(), close() */


int main(int argc, char *argv[])
{
 int fd;
 fd = open("/sys/class/gpio/export", O_WRONLY);
 write(fd, "11", 3); // Include null!

what's the meaning of  write(fd, "11", 3); // Include null!

Regards

He

Hi,

what's the meaning of  write(fd, "11", 3); // Include null!

This means writing 11 into export file.

Regards

AnilKumar

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Hi AnilKumar

I don't know what the "11" mean.  if i want control GP1[1],  in the OMAPL138 datasheet:

                                     GPIO Register Bits and Banks  Associated With GPIO  Signals

GPIO Pin Number      GPIO Signal Name        Bank Number    Control Registers     Register Bit     Register Field

               1                              GP0[0]                                    0                register_name01              Bit 0              GP0P0

               2                              GP0[1]                                    0                register_name01              Bit 1              GP0P1

               ……                   ……                   ……

               18                            GP1[1]                                    1                register_name01              Bit 17              GP1P1

 Can  I use it like this  write(fd,“18",3) ?    right?  

int fd;
fd = open("/sys/class/gpio/export", O_WRONLY);
write(fd, "18", 3); // Include null!
close(fd);

fd = open("/sys/class/gpio/gpio18/direction", O_WRONLY);
write(fd, "out", 4);
close(fd);

fd = open("/sys/class/gpio/gpio18/value", O_WRONLY);
while(1){
write(fd, "0", 2);
sleep(3);
write(fd, "1", 2);
sleep(3);
}
close(fd);

When  I detect the pin GP1[1],  I can't get the value I set to it .  Why?

Regards

He

Hi He,

The way you are using are correct,

Make sure that pinmux settings are proper, refer OMAPL138 GPIO user guide for more details

Below post will help you on GPIO functionality.

http://e2e.ti.com/support/dsp/davinci_digital_media_processors/f/716/p/182160/657204.aspx#657204

Regards

AnilKumar

Please mark this Forum post as answered via the Verify Answer button below if it helps answer your question.  Thanks!

Hi,AnilKuma

Thank you for your quick reply. But I still have problem to find the pinmux setting fuction.

My PSP is: OMAP_L138_arm_1_00_00_08\DaVinci-PSP-SDK-03.20.00.08\ 

I tried to add below in /arch/arm/mach-davinci/include/mach/mux.h

/* GPIO function */

DA850_GPIO2_6,
DA850_GPIO2_8,

DA850_GPIO1_1,//my add

and add in /arch/arm/mach-davinci/da850.c  in static const struct mux_config da850_pins[] = {}   fuction

/* GPIO function */
MUX_CFG(DA850, GPIO2_6, 6, 4, 15, 8, false)
MUX_CFG(DA850, GPIO2_8, 5, 28, 15, 8, false)

MUX_CFG(DA850, GPIO1_1, 4, 24, 15, 8, false)  //my add

after rebuilt the kernel When  I detect the pin GP1[1],  I still can't get the value I set to it .  Is I wrong?   Is there any other place I must modify?

Regards

He

Hi Ram

Do you solve you problem? I have the same problems with you ?  

Are you success setting pinmux?  How to do it.

Below is my problems.

Hi Norman
I have some trobles in pinmux settings.
My PSP is: OMAP_L138_arm_1_00_00_08\DaVinci-PSP-SDK-03.20.00.08\
I tried to add below in /arch/arm/mach-davinci/include/mach/mux.h
/* GPIO function */
DA850_GPIO2_6,
DA850_GPIO2_8,
DA850_GPIO1_1,//my add

and add in /arch/arm/mach-davinci/da850.c in static const struct mux_config da850_pins[] = {} fuction
/* GPIO function */
MUX_CFG(DA850, GPIO2_6, 6, 4, 15, 8, false)
MUX_CFG(DA850, GPIO2_8, 5, 28, 15, 8, false)
MUX_CFG(DA850, GPIO1_1, 4, 24, 15, 8, false) //my add
after rebuilt the kernel When I detect the pin GP1[1], I still can't get the value I set to it . Is I wrong? Is there any other place I must modify?

Regards
He

Hi He,

Make sure that you have written the correct value to corresponding register

http://e2e.ti.com/support/embedded/linux/f/354/p/167148/609581.aspx#609581

Regards

AnilKumar

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Hi Anil

I do it like this:

# echo 18 > /sys/class/gpio/export
~# ls  /sys/class/gpio/gpio18
active_low  edge        subsystem   value
direction   power       uevent
:~# echo out > /sys/class/gpio/gpio18/direction
~# echo 0 > /sys/class/gpio/gpio18/value
~# cat /sys/class/gpio/gpio18/value
1
~# echo 1 > /sys/class/gpio/gpio18/value
~# cat /sys/class/gpio/gpio18/value
1

~# echo 0 > /sys/class/gpio/gpio18/value
~# cat /sys/class/gpio/gpio18/value
1

why the value can not be change?  when I use "echo 29 > /sys/class/gpio/export "  , the export29   value can changed as I set.

The  file 'value' is R/W.

Did you call "davinci_cfg_reg(gpio_pin)" to set pinmux for gpio18 besides adding entries in mux.h and da850.c?

BTW, gpio1[1] is gpio17 instead of gpio18.

Regards,

Yan

Hi He,

Make sure that you are configuring the same GPIO pin.

You are trying to add pinmux for GPIO1_1 (18th gpio pin) means gpio 17 in your previous post.

Here you are changing the value of gpio 18 (19th pin), use the same GPIO at both the places

Can you check these

echo 17 > /sys/class/gpio/export

echo "out" > /sys/class/gpio/gpio17/direction

echo 0 > /sys/class/gpio/gpio17/value

echo 1 > /sys/class/gpio/gpio17/value

Note: Can you check the status of pinmux register after kernel boots-up

Regards

AnilKumar

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