Implementation of Embedded OS

Lab3 Linux Kernel Modules

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Goal Learn how to write Linux kernel modules.

2014/4/8* source: The Linux Device Drivers, 3rd

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Environment Host System

Windows XP Build System

VirtualBox + Ubuntu 8.04 Target System

Creator XScale PXA270 Software

Drivers for Creator PXA270 LCD, 8-bit LED lamps, and 4-digit 7-segment LED.

You can download them from RSWiki IEOS Course Software

2014/4/8

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First Step

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Finish lab2-kernel first. Please make sure you have modified the flash

partition in Linux and flashed the correct file system (20MB).

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Linux Device Drivers

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Three major types Character device driver Block device driver Network device driver

Other types USB driver PCI driver ……

UserMode

KernelMode

Hardware

Application

Physical Device

System Call Interface

Virtual File System (VFS)

Buffer Cache

NetworkSubsystem

Character Device Driver

BlockDevice Driver

NetworkDevice Driver

Device Interface

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A Simple Kernel Module

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#include <linux/module.h> /* Needed by all modules */#include <linux/kernel.h> /* Needed for KERN_INFO */#include <linux/init.h> /* Needed for the macros */

static int __init init_hello(void){ printk(KERN_INFO "Hello, world\n"); return 0;}

static void __exit cleanup_hello(void){ printk(KERN_INFO "Goodbye, world\n");}

module_init(init_hello);module_exit(cleanup_hello);

MODULE_LICENSE("GPL"); /* License type of this module */MODULE_AUTHOR("DRIVER_AUTHOR"); /* Who wrote this module */MODULE_DESCRIPTION("DRIVER_DESC"); /* What does this module do */

initial function

cleanup function

declaration of initial/cleanup functions

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Makefile for Kernel Modules

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Suppose the filename of the module source is hello.c. Write a Makefile like this:

Type “make” to compile the module. Then transfer the output file hello.ko to the

target board. Type “insmod hello.ko” to load the module and

“rmmod hello” to remove the module.

obj-m += hello.o

all:make -C <kernel path> M=$(PWD) modules

clean:make -C <kernel path> M=$(PWD) clean

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Module Parameters

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You can define module parameters as follows.

You can pass the argument when loading the module as follows. $ insmod hello.ko myint=123

Further information about module parameters can be found on the websites listed in References.

/* Needed for the macro module_param */#include <linux/moduleparam.h>

static int myint = 0; /* define a integer variable */

/* declare the variable as a module parameter */module_param(myint, int,

S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP);

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Virtual File System (VFS) (1/2)

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User processes can communicate with device drivers through several ways, and VFS is the most common one.

A device driver can define a set of file operations including open, read, write, ioctl, etc., and associate it with an device number (inode).devno = MKDEV(MAJOR_NUM, MINOR_NUM);register_chrdev_region(devno, MAX_MINORS, MODULE_NAME));cdev_init(pcdev, &fops);cdev_add(pcdev, devno, MAX_MINORS);

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Virtual File System (VFS) (2/2)

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A process can use ordinary file I/O functions to access the device. First, create the corresponding file at /dev. $ mknod /dev/demo c <MAJOR_NUM>

<MINOR_NUM> In lab2, the major number is 120 and the minor

number is 0. Then, open the file /dev/demo and use the function

ioctl to control the device.

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An Example of the User Programs

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Please use the cross compiler to compile this program.#include <unistd.h>

#include <sys/fcntl.h>#include <sys/ioctl.h>#include <stdio.h>#include "creator_pxa270_lcd.h"

int main(){ int fd;

if((fd = open("/dev/demo", O_WRONLY)) < 0){ perror("couldn't open /dev/demo"); return 1; }

ioctl(fd, _7SEG_IOCTL_ON, 0);

close(fd);

return 0;}

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Lab Requirements

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Compile the kernel module. Write a Makefile for the driver provided. Compile the driver as a module and load it into Linux.

Implement a stopwatch app. The resolution should be in 0.1 seconds. The value of the counter should be display on the 4-

digit 7-segment LED in decimal form. It can be started, suspended, resumed, and reset by

pressing the buttons of the keypad. Please refer to the reference PDFs available on

our course website if you have any questions about the driver.

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References

2014/4/8

Linux Device Drivers, Third Edition http://lwn.net/Kernel/LDD3/

The Linux Kernel Module Programming Guide http://

www.tldp.org/LDP/lkmpg/2.6/html/lkmpg.html