Lecture for Lab 3, Exp1 of EE505

(Developing Device Driver)

T.A. Chulmin KimCoreLab.

Mar, 11, 2011[XenSchedulerPaper_Hotcloud-commits] r21 - /

Contents Introduction to Device Driver

Implementation of Device Driver

Usage of Device Driver

Problems

Environment & Policies

Introduction to Device Driver

What is Device Driver?

Introduction to Device Driver

What is Device Driver?

Software

Hardware

Introduction to Device Driver

Inside of Device Driver

Basically, it is usually generated by C code. In other word, it can be simple as much as ‘hello world’ in C

programming. You can freely imagine your device driver structure.

Even though it is not linked with real HW, it works.

Closely related with kernel. (use of system calls)

Introduction to Device Driver

Kinds of Device Drivers Character Device

Bypass Buffer Cache Serialized Data User receives Row Data of the device Ex. Terminal, video card, sound card…

Block Device Through Buffer Cache Random Accessible Ex. HDD, CDROM …

Network Device Ex. Ethernet

Introduction to Device Driver

How can we access to the device driver? Through Device File (special file)

In the previous lab, you heard that /dev/sdb to mount.

Char device and Block device have this file. ‘Mknod /dev/dummy c 254 0’ – creation of the device

file.

Real Usage (system call)   fd = open("/ dev/dummy ", O_RDWR);

 write(fd,buf,1);  read(fd,buf,1);  close(fd);

Implementation of Device Driver

Specification of Dummy Device Driver No linkage with Real HW. Using printk, only printout the name of the

device driver operation called by a user. Implementations

Module init and cleanup 4 Operations in Dummy Device Driver

dummy_read : read system call dummy_write : write system call dummy_open : open system call dummy_release : close system call

Implementation of Device Driver

How can we implement it? Initialization (in init_module function)

Mapping a device file with the device driver

Registration of a Char Device : offered by OS Needs Major Number, Name, and File_operation

Structure of the device driver.

int register_chrdev( unsigned int major, const * name, struct file_operations * fops);

int register_chrdev( unsigned int major, const * name, struct file_operations * fops);

struct file_operations dummy_fops = { open : dummy_open, // open    read :  dummy_read,               // read     write : dummy_write,               // write     release : dummy_release,      // release };

Mapping system calls with the internal functions of the device drivers

Implementation of Device Driver

How can we implement it?#define DUMMY_MAJOR_NUMBER 254 struct file_operations dummy_fops = { open : dummy_open, // open    read :  dummy_read,               // read     write : dummy_write,               // write     release : dummy_release,      // release };

char devicename[20]; int init_module(void) {         printk("init module\n");         strcpy(devicename, "Dummy_Driver");         register_chrdev( DUMMY_MAJOR_NUMBER, devicename, &dummy_fops);         return 0; }

void cleanup_module(void) {                  printk("Clean Up Module\n");         unregister_chrdev(DUMMY_MAJOR_NUMBER,devicename); }

Implementation of Device Driver

How can we implement it?

How can we build this? T.A. and the material will show you the way.

int dummy_open(struct inode *inode, struct file *file) {         printk("Open call \n");         return 0; }

ssize_t dummy_read(struct file *file, char *buffer,   size_t length, loff_t *offset) {         printk("Here is Read Call \n");         buffer[0] = 0x34;         return 0; }

ssize_t dummy_write(struct file *file, const char *buffer, size_t length,  loff_t *offset) {         printk("Here is Write Call [%x]\n ",buffer[0]);         return 0; }

Usage of Device Driver Module Instructions

Insmod dummy.ko -> the module output file built Rmmod dummy Check the kernel message -> since we used

printk to see the device driver operations. Test this through your own user application.

Simple C program appeared in the material. Insmod should be done first before executing the

user application.

Problems 1. device driver with FIFO queue

FIFO Queue structure

In (write)& Creation of Entry in the Queue

Out (read)& Deletion of Entry

APP1 APP2Check the written data sequence and the read data sequence are same or not.

Problems 2. flush operation makes queue

empty

APP1 APP2APP3

Flush OP

Thrash all the entries in the queue

Problems 3. Make a block device driver.

With simple write and read operation. The unit of data of read and write should

be a block. (kernel structure should be used)

Hints are given in the material. Further hints will be given by T.A. Not Necessary, it is the extra-credit

problem. But should be in the report.

Environment & Policies Environment

Same with Lab2

Policies Same with Lab2 Due : 3/25 11:59 PM Submission :

(hard copy) : not decided yet. (soft copy) : cmkim@core.kaist.ac.kr

Appendix Queue Example

Appendix Queue Example

Appendix Queue Example

#define QUEUE_SIZE 1024typedef {

int head, tail; int item[QUEUE_SIZE];} CQ_t;static inline void InitCQ(CQ_t *q)

{ q->head = q->tail = 0;}static inline int IsFull(CQ_t *q) {

return ( (q->head+1)%QUEUE_SIZE == q->tail );

}static inline int IsEmpty(CQ_t *q)

{return (q->head == q->tail);

}

#define QUEUE_SIZE 1024typedef {

int head, tail; int item[QUEUE_SIZE];} CQ_t;static inline void InitCQ(CQ_t *q)

{ q->head = q->tail = 0;}static inline int IsFull(CQ_t *q) {

return ( (q->head+1)%QUEUE_SIZE == q->tail );

}static inline int IsEmpty(CQ_t *q)

{return (q->head == q->tail);

}

int Queue(CQ_t *q, int value){

if (q==NULL) return -1;if (IsFull(q)) return -2;q->item[q->head] = value;q->head = (q->head + 1)%QUEUE_SIZE;return 0;

}

int Dequeue(CQ_t *q, int *value){

if (q==NULL || value==NULL) return -1;if (IsEmpty(q)) return -2;*value = q->item[q->tail];q->tail = (q->tail + 1)%QUEUE_SIZE;return 0;

}

int Queue(CQ_t *q, int value){

if (q==NULL) return -1;if (IsFull(q)) return -2;q->item[q->head] = value;q->head = (q->head + 1)%QUEUE_SIZE;return 0;

}

int Dequeue(CQ_t *q, int *value){

if (q==NULL || value==NULL) return -1;if (IsEmpty(q)) return -2;*value = q->item[q->tail];q->tail = (q->tail + 1)%QUEUE_SIZE;return 0;

}

Thank You! Good Luck with your finishing.