1. Lab 12 Department of Computer Science and Information Engineering National Taiwan University Lab12 – Driver 2014/12/16 1 /21

2. Lab 12 Department of Computer Science and Information Engineering National Taiwan University  Understand the architecture of Linux device drivers and learn how to control the LCD of PXA270. 2014/12/16 2 /21

3. Lab 12 Department of Computer Science and Information Engineering National Taiwan University  Host System  Windows XP  Build System  VirtualBox + Ubuntu 8.04  Target System  Creator XScale PXA270  Software  Linux kernel, please refer to Lab5  BusyBox, please refer to Lab6  Creator PXA270 LCD driver  You can download all software from RSWiki CSL Course SoftwareRSWiki CSL Course Software 2014/12/16 3 /21

4. Lab 12 Department of Computer Science and Information Engineering National Taiwan University  What are device drivers?  Make a particular piece of hardware respond to a well-defined internal programming interface.  Hide completely the details of how the device works.  User activities are performed by means of a set of standardized calls that are independent of the specific driver.  Mapping those calls to device-specific operations that act on real hardware is then the role of a device driver. 2014/12/16 4 /21

5. Lab 12 Department of Computer Science and Information Engineering National Taiwan University  There are three fundamental types of Linux device drivers.  Character device driver  Block device driver  Network device driver  We will only learn how to write character device drivers in this Lab. 2014/12/16 5 /21

6. Lab 12 Department of Computer Science and Information Engineering National Taiwan University  A Linux device driver can be divided into two parts.  Virtual device driver  Physical device driver 2014/12/16 6 /21 filenamedescription typ e major numb er minor numb er /dev/ttyS 0 First UART serial port ch ar 464 User Kernel Device Driver Hardware Device File implement chipset control functions define I/O wrapper functions define chipset header implement system calls register driver (VFS) define file_operations Virtual Device Driver Physical Device Driver

7. Lab 12 Department of Computer Science and Information Engineering National Taiwan University  Define file_operations and implement system calls. #include struct file_operations dev_fops = { open: dev_open, read: dev_read, write: dev_write, release: dev_release, ioctl: dev_ioctl, }; 2014/12/16 7 /21 Implement these functions

8. Lab 12 Department of Computer Science and Information Engineering National Taiwan University  Register a character device driver in the initial function. int register_chrdev(unsigned int major, const char *name, struct file_operations *fops);  Unregister a character device driver in the exit function. int unregister_chrdev(unsigned int major, const char *name); 2014/12/16 8 /21

9. Lab 12 Department of Computer Science and Information Engineering National Taiwan University  Two common approaches to access hardware.  Memory mapped I/O  Port I/O  Memory mapped I/O:  Access I/O (port) in the same way as that memory is accessed.  For example, there is a device that has a 8 bit I/O port connected to the system, and its address is mapped at 0x10000. We can read and write the I/O port like this: #define DATA_PORT (*(volatile char*)(0x10000)) char read_b() {return DATA_PORT;} void write_b(char data) {DATA_PORT = data;} 2014/12/16 9 /21

10. Lab 12 Department of Computer Science and Information Engineering National Taiwan University  Port I/O:  If the I/O system has its own address independent of memory, then it is port I/O.  Register the I/O port. E.g., 0x378. if (check_region(0x378, 1)) { printk(" parallelport: cannot reserve 0x378\n"); } else { request_region(0x378, 1, "demo"); }  Use the I/O commands. char data = inb(0x378);//Read data form the port 0x378 outb(data, 0x378); //Write data to the port 0x378  Release I/O port. release_region(0x378, 1); 2014/12/16 10 /21

11. Lab 12 Department of Computer Science and Information Engineering National Taiwan University  In Linux, devices are accessed in the same way as that files are accessed.  These device files are normally in the /dev directory.  We can create a device file by the following command.  % mknod /dev/demo c  More details about mknod can be found at  鳥哥的 Linux 私房菜. 鳥哥的 Linux 私房菜  So, we can manipulate the device via reading/writing its device file.  Most Linux drivers are implemented as kernel modules. 2014/12/16 11 /21

12. Lab 12 Department of Computer Science and Information Engineering National Taiwan University  A kernel module is an object file that contains code to extend the running kernel of an operating system.  Typically used to add support for new hardware and/or filesystems, or for adding system calls.  When the functionality provided by an kernel module is no longer required, it can be unloaded in order to free memory and other resources. 2014/12/16 12 /21

13. Lab 12 Department of Computer Science and Information Engineering National Taiwan University  % insmod module.ko  This command is used to insert a module into the kernel.  It doesn’t modify the module’s disk file, but rather than in-memory copy.  % rmmod module.ko  This command is used to remove a module from the kernel.  This command invokes the delete_module() system call, which calls cleanup_module() in the module itself if the usage count is zero or returns an error otherwise.  % lsmod  List the module currently linked to Linux. 2014/12/16 13 /21

14. Lab 12 Department of Computer Science and Information Engineering National Taiwan University #include #include #include static int init_demo(void) { printk("Hello World!\n"); return 0; } static void cleanup_demo(void) { printk("Goodbye World!\n"); } module_init(init_demo); module_exit(cleanup_demo); MODULE_LICENSE("Dual BSD/GPL"); 2014/12/16 14 /21 initial function cleanup function declaration of initial/cleanup functions

15. Lab 12 Department of Computer Science and Information Engineering National Taiwan University  Note that the messages in printk will be showed in the kernel, you can use dmesg command to check the messages.  We need to compile this module with kernel, and the result will be demo.ko. Here is the example of Makefile. CC = arm-unknown-linux-gnu-gcc obj-m := demo.o all: make -C M=$(PWD) modules clean: make -C M=$(PWD) clean 2014/12/16 15 /21

16. Lab 12 Department of Computer Science and Information Engineering National Taiwan University  Open the file /dev/demo and test its read and write functions just like a normal file. #include #include #include int main() { int fd, data; if((fd = open("/dev/demo", O_RDWR)) < 0) { printf("couldn't open /dev/demo\n"); return 1; } write(fd, "Hello World!", 13); read(fd, &data, 4); close(fd); return 0; } 2014/12/16 16 /21

17. Lab 12 Department of Computer Science and Information Engineering National Taiwan University  Now we add the PXA270 LCD driver to Linux kernel as a kernel module.PXA270 LCD driver  Step 1: extract the driver, and copy to your Linux kernel source in Lab5.  Step 2: compile modules.  We build the driver as a module.  % make menuconfig  “Device Drivers”  “Character devices”  “Creator-pxa270 LCD”  % make modules  The result creator-pxa270-lcd.ko is in drivers/char/.  Step 3: check these commands lsmod, insmod, rmmod in your root filesystem.  If you don’t have any of these, please refer to Lab6 and copy a new root filesystem 2014/12/16/21 17

18. Lab 12 Department of Computer Science and Information Engineering National Taiwan University  Step 4: transfer creator-pxa270-lcd.ko to PXA270.  Step 5: insert the module to Linux.  % insmod creator-pxa270-lcd.ko  You will see “good” on the 4-Digit 7 segment LED.  Tips  If you want to reload the module, do not forget to remove the running module first.  % rmmod creator-pxa270-lcd.ko 2014/12/16/21 18

19. Lab 12 Department of Computer Science and Information Engineering National Taiwan University  Please refer to previous slides to implement a simple driver for a virtual device demo.  Create the device with major number 60 and minor number 0.  When you initialize module, delete module, open device, close device, read device and write device, please print messages.  E.g., printk(“Open command is issued.”);  You don’t need to implement the “real work” of functions.  Write an application to control the LCD.  Trace the driver code and know how it works.  Do not forget to create the LCD device file.  % mknod /dev/lcd c 120 0 2014/12/16/21 19

20. Lab 12 Department of Computer Science and Information Engineering National Taiwan University  You can refer to the PXA270 LCD driver to implement your demo driver.  See the struct file_operations and know how to implement these system calls.  Also see how to control LCD by ioctl commands.  You may want to define some ioctl commands in your application.  You can refer to Writing device drivers in Linux: A brief tutorial for more information.Writing device drivers in Linux: A brief tutorial 2014/12/16/21 20

21. Lab 12 Department of Computer Science and Information Engineering National Taiwan University  Show the messages of accessing the demo device.  Including open, close, read, write, initial, remove.  Show more than one message on LCD from applications.  Show your group number, and your student IDs. 2014/12/16/21 21