How to use GPIOs
Contents
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, Ubuntu 10.04 with Linaro Toolchain, IGEP v2 RC5 and GPIO driver wrote by Dave Hylands. There are more ways to use GPIOs in IGEP v2, but this one is simple and reliable.
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 source code from author website using the next command:
wget -r -np http://svn.hylands.org/linux/gpio/
Due the source Makefiles are implemented for Gumstix SDK, it is necessary change some constants for compile with our Host. These constants are:
In files:
$/svn.hylands.org/linux/gpio/app/Makefile
$/svn.hylands.org/linux/gpio/lib/Makefile
Search lines:
OVEROTOP ?= /home/gumstix/overo-oe CROSS_COMPILE ?= $(OVEROTOP)/tmp/sysroots/x86_64-linux/usr/armv7a/bin/arm-angstrom-linux-gnueabi-
Replaced by your cross compiler path, for example:
OVEROTOP ?= / CROSS_COMPILE ?= $(OVEROTOP)/usr/bin/arm-linux-gnueabi-
In file:
$/svn.hylands.org/linux/gpio/modules/Makefile
Search lines:
OVEROTOP ?= /home/gumstix/overo-oe #CROSS_COMPILE ?= $(OVEROTOP)/tmp/cross/armv7a/bin/arm-angstrom-linux-gnueabi- CROSS_COMPILE ?= $(OVEROTOP)/tmp/sysroots/x86_64-linux/usr/armv7a/bin/arm-angstrom-linux-gnueabi- KERNEL_PATH ?= ../../../../../gumstix/overo-oe/tmp/sysroots/overo-angstrom-linux-gnueabi/kernel ARCH ?= arm
Replaced by your cross compiler path and your kernel source used path, for example:
OVEROTOP ?= / #CROSS_COMPILE ?= $(OVEROTOP)/tmp/cross/armv7a/bin/arm-angstrom-linux-gnueabi- CROSS_COMPILE ?= $(OVEROTOP)//usr/bin/arm-linux-gnueabi- KERNEL_PATH ?= ../../../../../<your kernel source path used> ARCH ?= arm
Go to: $/svn.hylands.org/linux/gpio/Makefile and compile all source code downloaded using make command.
Send binaries created from Host to Igep v2.
Install binaries via IGEP
Log with root user to install binaries.
Install module
Go to:$/svn.hylands.org/linux/gpio/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 than this:
root@localhost:~/svn.hylands.org/linux/gpio/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 dynamic library
Go to:$/svn.hylands.org/linux/gpio/lib/. libgpio.so will be found here.
If a program is link with dinamic libraries, Linux kernel find this ones in a specific paths when program is executed. Now is necessary link the libgpio.so path to the envireonment variable LD_LIBRARY_PATH, use the following commnad:
export LD_LIBRARY_PATH=/root/svn.hylands.org/linux/gpio/lib/
Check that libgpio.so is linked correctly. Go to:$/svn.hylands.org/linux/gpio/app, gpio program will be found here. Type next command:
ldd gpio
ldd command list program dependencies and show its paths. The result will be similar than this:
root@lSee if libgpio.so is found it. If you execute program in bash without linking library dependencies, bash give you a error message. ocalhost:~/svn.hylands.org/linux/gpio/app# ldd gpio libgpio.so => /root/svn.hylands.org/linux/gpio/lib/libgpio.so (0x40197000) libc.so.6 => /lib/libc.so.6 (0x401a0000) /lib/ld-linux.so.3 (0x4008a000)
Now you can execute example program gpio.
Execute app
Go to:$/svn.hylands.org/linux/gpio/app, gpio will be found here.
To make sure that libgpio.so can be founded as a dependency of gpio program use the following command:
ldd gpio
See if libgpio.so is found it. If you execute program in bash without linking library dependencies, bash give you a error message.