IMX LED Driver TP
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Proposal
The goal of this tutorial is to build from scratch a simple led driver wire on GPIO of the iMX. This document will describes step by step how to implement a such driver
Howto Load/unload modules : "hwmon" module
Loading a module is quite simple once it is compiled and is present in the rootfs of the apf board. All the compiled driver modules are in the "/lib/modules/<kernel version>/kernel" in the apf rootfs. To list all the loadable modules by the kernel in the board type :
# find /lib/modules/`uname -r`/kernel -name "*.ko" /lib/modules/2.6.27.13/kernel/sound/arm/snd-imx-alsa-tsc2102.ko /lib/modules/2.6.27.13/kernel/sound/arm/snd-mx2.ko /lib/modules/2.6.27.13/kernel/sound/core/snd-page-alloc.ko /lib/modules/2.6.27.13/kernel/sound/core/snd-timer.ko /lib/modules/2.6.27.13/kernel/sound/core/snd.ko /lib/modules/2.6.27.13/kernel/sound/core/snd-pcm.ko /lib/modules/2.6.27.13/kernel/sound/soundcore.ko /lib/modules/2.6.27.13/kernel/drivers/spi/tsc2102.ko /lib/modules/2.6.27.13/kernel/drivers/scsi/scsi_wait_scan.ko /lib/modules/2.6.27.13/kernel/drivers/hwmon/hwmon.ko /lib/modules/2.6.27.13/kernel/drivers/input/touchscreen/tsc2102_ts.ko /lib/modules/2.6.27.13/kernel/drivers/video/backlight/lcd.ko /lib/modules/2.6.27.13/kernel/drivers/video/backlight/backlight.ko /lib/modules/2.6.27.13/kernel/drivers/armadeus/max1027/max1027.ko /lib/modules/2.6.27.13/kernel/drivers/armadeus/backlight/imx_bl.ko
For example, I will load "/lib/modules/2.6.27.13/kernel/drivers/hwmon/hwmon.ko" module :
# modprobe hwmon #
To list all mod loaded :
# lsmod Module Size Used by Not tainted hwmon 2356 0
To unload it just type :
# rmmod hwmon #
TBC
Howto Build a simple char module and load/unload it : the "Hello World" module
The "Hello World" module code is quite simple have only load and unload fonction.
Create required folder and files
Create a hello folder in <armadeus_directory>/target/linux/modules/. On the host computer type :
cd <armadeus_directory>/target/linux/modules/ mkdir hello
Hello.c source file
#include <linux/module.h> /* Default module librairies TBC */ #include <linux/kernel.h> /* Print "Hello, world\n" with KERN_ALERT level (stdio TBC) */ static int hello_init(void){ printk(KERN_ALERT "Hello, world\n"); return 0; } /* Print "Goodbye, cruel world\n" with KERN_ALERT level (stdio TBC) */ static void hello_exit(void){ printk(KERN_ALERT "Goodbye, cruel world\n"); } module_init(hello_init); /* Set hello_init function as the module init one (called when module load) */ module_exit(hello_exit); /* Set hello_exit function as the module exit one (called when module unload) */ MODULE_LICENSE("GPL"); /* Set the license module */
Makefile file
# Part executed when called from kernel build system: ifneq ($(KERNELRELEASE),) obj-$(CONFIG_ARMADEUS_LED_XAV_DRIVER) += hello.o #hello-objs := hello.o # Part executed when called from standard make in this directory: # (preferably use Makefile in parent directory) else ARMADEUS_BASE_DIR=../../../.. include $(ARMADEUS_BASE_DIR)/Makefile.in KDIR := $(ARMADEUS_LINUX_DIR) PWD := $(shell pwd) # Armadeus custom drivers common targets: include ../Makefile.in endif
TBC