Openwrt compilation driver module (write code at any position outside the openwrt source code, and compile independently in a modular manner.Ko)

One 、 Hardware platform

        MT7620（A9 kernel ）

Two 、 software platform

       1、Ubuntu 12.04 

       2、openwrt official 15.05 edition SDK Development kit

3、 ... and 、 Functional specifications

    This article mainly introduces , How to compile openwrt Driver module .
    Recently, I am sorting openwrt The driver , But online information , Most of it is in openwr Source code package Under the table of contents , Create folder , And then in openwrt Compile under Directory . Although this method can be compiled , But it is not particularly convenient to maintain . For example, compile a module separately , It also depends on openwrt Of SDK package . such , Every time you need to add a drive module , All in SDK Create a directory under the package .
    I prefer to drive the module to create a folder separately , The path is not restricted . This is convenient for code maintenance and management , And in git perhaps svn Easy to upload and download , And openwrt Source code SDK Subcontracting leave .
    This article , The main introduction is , Anywhere , Create your own folders and write drivers , Then compile the driver module . The biggest advantage is , The path of the code is unlimited . If you need to modify a driver , Just download the driver file , There is no need to update the whole openwrt SDK Development kit .

Four 、 Operation steps

      1、 To write C file

    In any folder , For example, the path of this article is /home/test/   Write code , The name is “hello.c”.

#include <linux/init.h>
#include <linux/module.h>
#include <linux/kernel.h>
/* hello_init ----  Initialization function , Called when the module is loaded , If the load is successful, return 0  Otherwise return to non 0 value  */
static int __init hello_init(void)
{    
    printk("I bear a charmed life.\n");    
	return 0;
}

/* hello_exit ----  Exit function , Called when the module is unloaded  */
static void __exit hello_exit(void)
{    
	printk("Out, out, brief candle\n");
}

module_init(hello_init);
module_exit(hello_exit);
MODULE_LICENSE("GPL");

    2、 To write makefile

Compiled using makefile file , The file name is called “makefile”.

explain ：

In this paper ,openwrt Of SDK The storage path of the development package is  /home/sky/develop/openWrt/openwrt/

openwrt Download the kernel , The storage path is  /home/sky/develop/openWrt/openwrt/build_dir/target-mipsel_24kec+dsp_glibc-2.21/linux-ramips_mt7620/linux-3.18.29/

openwrt Of gcc Cross compile toolchain , Path is ：/home/sky/develop/openWrt/openwrt/staging_dir/toolchain-mipsel_24kec+dsp_gcc-4.8-linaro_glibc-2.21/bin/

For this article openwrt Of SDK package ：

(1） The cross compiler tool chain is glibc2.21

(2） The target chip is selected as mt7620

stay makefile in , Illustrates the gcc and openwrt Of SDK Package path ,makefile The contents are as follows ：

######################################## hello ################################
obj-m = hello.o
PWD=$(shell pwd)
KERNEL_DIR=/home/sky/develop/openWrt/openwrt/build_dir/target-mipsel_24kec+dsp_glibc-2.21/linux-ramips_mt7620/linux-3.18.29/
TOOLCHAIN="/home/sky/develop/openWrt/openwrt/staging_dir/toolchain-mipsel_24kec+dsp_gcc-4.8-linaro_glibc-2.21/bin/mipsel-openwrt-linux-gnu-"

###############################################################################
all:
	make -C $(KERNEL_DIR) \
	ARCH=mips \
	CROSS_COMPILE=$(TOOLCHAIN) \
	M=$(PWD) \
	modules
	
clean:
	rm -f *.ko
	rm -f *.o
	rm -f *.mod.c
	rm -f *.mod.o
	rm -f *.order
	rm -f *.sysvers
  
#make command:
#make
#make clean

3、 compile

In the terminal , Compile , Enter the command ：  make  

Need to clear , Then enter the command ： make clean