2416 Development Record 2: The simplest helloworld driver

1. Write a helloworld driver

The driver source code is as follows:

#include

#include

static int hello_init(void)

{

   printk(KERN_INFO "BBBlackHelloModule enter!\n");

   return 0;

}

static void hello_exit(void)

{

   printk(KERN_INFO "BBBlackHelloModule exit!\n");

}

module_init(hello_init);

module_exit(hello_exit);

MODULE_AUTHOR("Zhao Yidong

MODULE_LICENSE("Dual BSD/GPL");

MODULE_DESCRIPTION("A sample bbblack hello module");

MODULE_ALIAS("a sample module");

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2. Write the driver makefile

According to the hellomodule of PC, modify the makefile file and edit the makefile of 2416 as follows:

#Makefile for .c

ARCH=arm

CROSS_COMPILE=arm-linux-

ifneq ($(KERNELRELEASE),)

    obj-m := HelloModule2416.o

else

#bbblack kernel

KERNELDIR ?= /home/zyd/soft/s3c2416/20140409_HELPER2416/Helper2416/source/s3c-linux.jyx

PWD := $(shell pwd)

modules:

    make -C $(KERNELDIR) M=$(PWD) ARCH=$(ARCH) CROSS_COMPILE=$(CROSS_COMPILE) modules

modules_install:

    make -C $(KERNELDIR) M=$(PWD) ARCH=$(ARCH) CROSS_COMPILE=$(CROSS_COMPILE) modules_install

app: app.c

    $(CROSS_COMPILE)gcc -o app app.c

clean:

    $(MAKE) -C $(KDIR) M=$(PWD) clean

endif

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3. Compile

When executing make modules, an error message  ERROR: Kernel configuration is invalid. 

It turns out that you need to compile the kernel first 

OK, go to the kernel directory /home/zyd/soft/s3c2416/20140409_HELPER2416/Helper2416/source/s3c-linux.jyx and execute the command 

make ARCH=arm CROSS_COMPILE=arm-linux- zImage 

Note that you must specify the target and compiler. Otherwise, the compiled version will be x86. 

After compiling the kernel, you can compile hellomodule. 

But when I downloaded the compiled hellomodule.ko driver file to the development board and ran it, an error occurred again. It seemed that the kernel was inconsistent. Oh my god! ! ! ! ! ! ! !

How to solve it? 

Starting from the cause, it is suggested that the kernel of the development board and the kernel compiled by the driver are inconsistent. 

The kernel of the development board can be viewed using the uname -r command as follows 

[root@jyxtec /root]# uname -r 

3.2.50+

When the development board starts, the following information is printed 

Linux version 3.2.50+ (d02cj@LinuxServer0) (gcc version 4.4.6 (crosstool-NG 1.14 

CPU: ARM926EJ-S [41069265] revision 5 (ARMv5TEJ), cr=00053177

Check the driver information as follows 

modinfo HelloModule2416.kofilename: HelloModule2416.ko 

alias: a sample module 

description: A sample bbblack hello module 

license: Dual BSD/GPL 

author: Zhao Yidong zmurder@outlook.com 

depends: 

vermagic: 3.2.50 mod_unload ARMv5 p2v8

The kernel of the driver is inconsistent with the kernel of the development board. Because I compiled the kernel before compiling the driver (why do I have to compile the kernel first? I can't compile the driver without compiling the kernel first!!!). The compiled kernel is inconsistent with the kernel on the development board! ! ! ! (Damn the development board vendor, the compiled kernel provided is different from the actual one!!) 

Well, now that we know the reason, it’s easy to solve. 

Use FTP (assuming FTP is configured) to download your compiled kernel zImage to the development board (refer to Section 3.3.4 of the Junyixing Development Board Manual, Download, Erase, Burn, and Specify Load.)

4. Install and uninstall the driver

At this time, you can use insmod again!!! Hahahahaha!! 

But the problem came up again. When using rmmod to uninstall the driver, it prompted (the reason is that busybox is different from the distribution Linux installation, and no corresponding directory is generated) 

rmmod: chdir(3.2.50): No such file or directory 

Well, here is the solution: 

Create a directory:  mkdir -p /lib/modules/$(uname -r) 

Copy your own driver to this directory

At this point, HelloModule is complete... It was hard!!