Linux Driver Overview

1. Linux Driver Overview 報告人: 陸述人 http://www.ntut.edu.tw/~s4599001

2. Operating System Linux • Operating system • Kernel space/User space • MMU • mutex/semaphore/interrupt • Task structure • ptrace/mmu/signal/task relation /process id • file/timer/semaphores/misc • Main algorithm • Signal handing • Interrupt • Tasklets • Bottom haves • Software interrupt –max 32 • Void open_sorftirq(int nr, void (*action) (structure softirq_action *, void *data) • Raise_softirq() • Scheduler • SCHED_FIFO/SCHED_RR/SCHED_OTHER

3. Mutex • Definition • In computer programming, a mutex is a program object that allows multiple program threads to share the same resource, such as file access, but not simultaneously. • Andrea Steinbach and Angelika Schofer, as a master's thesis at Rheinische Friedrich-Wilhelms University.

4. Semaphore • Definition • A semaphore is a protected variable (or abstract data type) and constitutes the classic method for restricting access to shared resources (e.g. storage) in a multiprogramming environment. • Sample • Dining philosophers problem • do not prevent all deadlocks • invented by Edsger Dijkstra and first used in the THE operating system

5. Semaphore Programming P(Semaphore s) { await s > 0 then s = s-1; /* must be atomic once s > 0 is detected */ } V(Semaphore s) { s = s+1; /* must be atomic */ } Init(Semaphore s, Integer v) { s = v; }

6. Operating System in Linux -3 • Driver: • Modprobe/Insmod/rmmod/lsmod • Built in kernel

7. Driver implementation in Linux • Driver specifications • Char drivers • Console • Serial port • Block drivers • DMA transfer • Network interfaces • IO port / IO memory

8. Driver implementation in Linux • Interrupt • int request_irq(unsigned int irq,void (*handler)(int, void *, struct pt_regs *),unsigned long flags,const char *dev_name,void *dev_id); • void free_irq(unsigned int irq, void *dev_id);

9. Writing Linux Device DriverHeader files #include <linux/kernel.h> #include <linux/module.h> #include <linux/version.h> #include <linux/config.h> #include <linux/init.h> #include <linux/types.h> #include <linux/fs.h>

10. Writing Linux Device DriverInitialize register (clear) static int test_open(struct inode *inodePtr, struct file *fp) { printk( "Enter open routine.\n" ); return 0; } static int test_release(struct inode *inodePtr, struct file *fp) { MOD_DEC_USE_COUNT; printk( "Enter test_release\n" ); return 0; }

11. Writing Linux Device DriverOperation static ssize_t test_read(struct file *fp, char *buf, size_t len, loff_t *offset) { printk( "Enter test_read\n" ); return len; } static ssize_t test_write(struct file *fp, char *buf, size_t len, loff_t *offset) { printk( "Enter test_write\n" ); return len; }

12. Writing Linux Device DriverMapping struct file_operations test_fops = { read: test_read, write: test_write, open: test_open, release: test_release, ioctl: test_ioctl, };

13. Writing Linux Device Driver static int test_ioctl(struct inode *inodePtr, struct file *fp, unsigned int cmd, unsigned long arg) { switch( cmd ){ default: break; } return 0; }

14. Entry point Exit point Writing Linux Device DriverEntry point V.S. Exit point int test_init_module(void) { register_chrdev( 100, testName, &test_fops ); printk( "Init test module\n" ); return 0; } void test_cleanup_module(void) { unregister_chrdev( 100, testName ); printk( "UnInit test\n" ); } module_init ( test_init_module ); module_exit ( test_cleanup_module );

15. Create Environment • Compiler • gcc -D__KERNEL__ -DMODULE -I/usr/src/linux-2.4.22/include -c -O -Wall drv.c -o drv.o • Make node • mknod /dev/test c 100 0 • Check node crw-rw-rw- 1 root dialout 4, 64 Jun 30 11:19 test crw-rw-rw- 1 root dialout 4, 65 Aug 16 00:00 ttyS1

16. Writing Application int main(int argc, char *argv[]) { int fd; char buf[256] = "Hello World!!"; fd = open( "/dev/test”, O_RDWR ); if ( fd == -1 ) { printf( "Open drv driver fail.[Application]\n“ ); return -1; } write( fd, buf, 6 ); close( fd ); return 0; }

17. Implementation in Embedded Linux • NOMMU (arm as example) • Uclinux(ww.uclinux.org) • MMU • http://www.arm.linux.org.uk/ • Other version • http://www.linux.org/

18. Implementation in Embedded Linux • The driver in embedded linux • Most implement in setting registers • The different in mmu/nommu • mmu • The same except less support • nommu • Almost no difference about address in user space /kernel sapce

19. Recommended Books && web sites • Linux Document Project • http://www.tldp.org • Advacend linux programming • http://www.advancedlinuxprogramming.com/alp-folder • Linux device drivers • http://www.xml.com/ldd/chapter/book/ • LINUX 核心程式設計 • Linux kernel programming M Beck • Understanding the LINUX KERNEL • Bovet & Cesati • Linux server hacks 駭客一百招 • Others—In the disk

20. Introduce to source navigator • http://sourcenav.sourceforge.net/

21. Q&A

22. Define in <linux/kernel.h> struct file_operations { struct module *owner; ssize_t (*read) (struct file *, char *, size_t, loff_t *); ssize_t (*write) (struct file *, const char *, size_t, loff_t *); int (*ioctl) (struct inode *, struct file *, unsigned int, unsigned long); int (*open) (struct inode *, struct file *); int (*release) (struct inode *, struct file *); };