topic GPIO access in i.MX Processors

GPIO access

JoshuaParrish — Tue, 27 Sep 2011 21:56:50 GMT

I was hoping to get some help with the imx53 loco board.

I can't get GPIO access to work.

I've set up the /sys/class sysfs support in the system using a new kernel.

With the ubuntu micro sd shipped with the qsb board (with newly flashed kernel)

I get permission denied when I try to echo 12 > /sys/class/gpio/export

With an ltib made rootfs and kernel

I get all the way through

echo 12 > /sys/class/gpio/export

echo out > /sys/class/gpio/gpio12/direction

echo 1 > /sys/class/gpio/gpio12/value

but the value doesn't change on the pin nor the actual file "value"

>cat /sys/class/gpio/gpio12/value

I can change the direction just fine, however the value still eludes me.

I've also tried this on different ports, still nothing works.

Re: GPIO access

fabio_estevam — Wed, 28 Sep 2011 02:36:23 GMT

What is the name of the pin you are trying to access?

Have you setup the IOMUX for this pin as GPIO?

Regards,

Fabio Estevam

Re: GPIO access

JoshuaParrish — Wed, 28 Sep 2011 15:21:00 GMT

Fabio,

I'm not sure I know how to do that.

Would you be willing to give me some instruction?

I've looked at the user guide where gpio is concerned and I'm a little confused on the pin muxing.

The exact pin I'd like to configure is GPIO_17 with an alternate name of GPIO1_12.

From the user guide and the hardware layout this pin can be probed via the 40th pin on J13 expansion header.

Re: GPIO access

fabio_estevam — Thu, 29 Sep 2011 01:46:40 GMT

No, GPIO_17 corresponds to GPIO7_12 in ALT1 mode.

So this is what you need to do:

1) Open arch/arm/mach-mx5/mx53_loco.c file and add the following enty to the mx53_loco_pads array:

MX53_PAD_GPIO_17__GPIO7_12,

This will let the kernel configure the MX53_PAD_GPIO_17 pad as GPIO7_12 function.

2) Rebuild and deploy the new kernel.

GPIO7_12 corresponds to (7-1)*32 + 12 = 204 GPIO number in Linux.

3) Access the GPIO as:

echo 204 > /sys/class/gpio/export

echo out > /sys/class/gpio/gpio204/direction

echo 1 > /sys/class/gpio/gpio204/value

echo 0 > /sys/class/gpio/gpio204/value

This should work fine.

Re: GPIO access

JoshuaParrish — Thu, 29 Sep 2011 05:43:43 GMT

Fabio,

Thankyou, for such a quick reply.

I had actually just discovered the GPIO7 issue. The User guide says that it is GPIO1_12, yet the io PIN mux tool available on the freescale site labeled it GPIO7_12, thank you for supporting that claim.

Also, thank you for going over the mux setup. The user guide just didn't make sense to me. I hope that I can return the favor.

Re: GPIO access

winstonrodrigue — Mon, 11 Mar 2013 06:58:14 GMT

Dear Fabio,

I am working on IMX53_smd (sabre tablet). since I was trying to toggle the LEDs in Linux ( charge and user debug D27, D32 from schematic ) which are connected to these pins :

MX53_PAD_EIM_D30__GPIO_30

MX53_PAD_PATA_DA_1__GPIO7_7

But these definitions are already registered in "iomux-mx53.h" and "mx53_smd.c"

so I tried to access the pins directly from sysfs like this....

for MX53_PAD_EIM_D30__GPIO_30 : "echo 94 > /sys/class/gpio/export

But when I do ls i count see any new directory..

for MX53_PAD_PATA_DA_1__GPIO7_7 I did "echo 199 > sys/class/gpio/export

Here also No directories created... I dont understand why .. Is it because these pins are already being used for Charge_done and USER_DEBUG ??

Another case :

I thought I will access the free GPIO pin on the expansion connector,

that is 40th pin on J78 i.e. MX53_PAD_GPIO_17__GPIO7_12

So i Added this pin in "../mach-mx5/mx53_smd.c" in static iomux_v3_cfg_t mx53_smd_pads[] array..

then i recompiled the kernel and deployed it, booted from SD card.

But when I try to access it : echo 204 > export

echo out > gpio204/direction

echo 1 > gpio204/value

But when i see the value it is still '0' and the Pin doesnt change. but direction has changed to "out"

What am I doing wrong here ... ??

Regards,

Winston.