How to use GPIOs

Overview

This How-To is meant to be a starting point for people to learn use GPIOs for IGEP v2 devices as quickly and easily as possible. For this how-to i used Linaro Headless with Kernel 2.6.35.y, Ubuntu 10.04 with Linaro Toolchain, IGEP v2 RC5 and GPIO driver (NOTE: Upload source code).

There are more ways to use GPIOs in IGEP v2, but this one is very simple.

Feedback and Contributing

At any point, if you see a mistake you can contribute to this How-To.

Compile GPIO driver source code via Host

Download GPIO driver (NOTE:Upload source code) and Kernel 2.6.35.y source code. Extract files.

Edit GPIO driver Makefile's:

-In files: $/app/Makefile and $/lib/Makefile, make sure that your CROSS_COMPILE path is correct.

-In file: $/modules/Makefile, make sure that your CROSS_COMPILE path is correct and type your Kernel 2.6.35.y path.

We will use the ncurses program for set up Kernel configuration, if you don't have this program installed then you must install it with this command:

sudo apt-get install ncurses-dev 

-Go to kernel path and type:

make ARCH=arm CROSS_COMPILE=arm-linux-gnueabi- menuconfig 

Exit Linux Kernel Configuration an return to Bash. Type:

make ARCH=arm CROSS_COMPILE=arm-linux-gnueabi- modules_prepare<br> 

File $/include/generated/autoconf.h was created

Finally compile GPIO driver, go to main Makefile path and compile all source code using make command.

Send binaries created from Host to Igep v2.

Install binaries via IGEP

Log with root user to install binaries.

Install module

Go to:$/modules and insert user-gpio-drv.ko into linux kernel with the following command:

insmod user-gpio-drv.ko

Check that user-gpio-drv.ko is currently loaded with the following command:

lsmod

The result will be similar at that:

root@localhost:~/gpio-driver/module# lsmod
Module                  Size  Used by
user_gpio_drv           1639  0 
omap_wdt                3411  0 
spidev                  4198  0 
iommu                   8558  0 
rtc_twl                 4411  0 
rtc_core               11187  1 rtc_twl
twl4030_keypad          2970  0 

The module is loaded until system halt.

Install shared library

Go to:$/lib. libgpio.so is here.

If a program is linked with shared libraries, Kernel seek in specific paths when program is executed. Now is necessary link the libgpio.so path to the environment variable LD_LIBRARY_PATH, use the following command:

export LD_LIBRARY_PATH=/root/gpio-driver/lib/

Check that libgpio.so is linked correctly. Go to:$/gpio-driver/app, gpio program is here. Type next command:

ldd gpio 

ldd command, print shared library dependencies. The result will be similar at that:

root@localhost:~/gpio-driver/app# ldd gpio
	libgpio.so => /root/gpio-driver/lib/libgpio.so (0x40197000)
	libc.so.6 => /lib/libc.so.6 (0x401a0000)
	/lib/ld-linux.so.3 (0x4008a000)

The shared library is linked until system halt. Now you can execute gpio example program.

Testing driver

To make sure than driver works well, make the next test. I used GPIO_136(sdmmc2_dat4) and GPIO_137(sdmmc2_dat5) because IGEP v2 RC5(without WIFI) don't use them by default:

NOTE: For more information visit this page.

Configure Mux

Go to:/sys/kernel/debug/omap_mux, and change this mux configuration:

echo 0x104>sdmmc2_dat4
echo 0x104>sdmmc2_dat5

Use cat command to check it:

cat sdmmc2_dat4
cat sdmmc2_dat5

The result will be similar at that:

root@localhost:/sys/kernel/debug/omap_mux# cat sdmmc2_dat4
name: sdmmc2_dat4.gpio_136 (0x48002164/0x134 = 0x0104), b ae4, t NA
mode: OMAP_PIN_INPUT | OMAP_MUX_MODE4
signals: sdmmc2_dat4 | sdmmc2_dir_dat0 | NA | sdmmc3_dat0 | gpio_136 | NA | NA | safe_mode

and

root@localhost:/sys/kernel/debug/omap_mux# cat sdmmc2_dat5
name: sdmmc2_dat5.gpio_137 (0x48002166/0x136 = 0x0104), b ah3, t NA
mode: OMAP_PIN_INPUT | OMAP_MUX_MODE4
signals: sdmmc2_dat5 | sdmmc2_dir_dat1 | cam_global_reset | sdmmc3_dat1 | gpio_137 | hsusb3_tll_stp | mm3_rxdp | safe_mode

Note: OMAP_PIN_INPUT=Input/Output pin and OMAP_PIN_OUTPUT=Output pin, for Read/Write test you need the first one. GPIO is configured in mode 4.

Read/Write test

Link GPIO_136 and GPIO_137 with a wire, these pins are located in J990 connector with numbers 7 and 9. I use the next connector to join them:

Now type next code:

root@localhost:~/gpio-driver/app# ./gpio input 136
root@localhost:~/gpio-driver/app# ./gpio output 137 0
root@localhost:~/gpio-driver/app# ./gpio get 136     
0
root@localhost:~/gpio-driver/app# ./gpio output 137 1
root@localhost:~/gpio-driver/app# ./gpio get 136     
1
root@localhost:~/gpio-driver/app# 

The results:

The code above shows that driver works properly, GPIO_136 is configured like input and GPIO_137 is configured like output with value 0, when read GPIO_136 the result is 0. To make sure that works well, configure GPIO_137 with value 1, now GPIO_136 reads 1.
This driver have more options like IRQ, but is not explained here.

Other examples:What can I do with IGEP0020#How_to_handle_the_gpio-LED.27s