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Understanding Linux Device Drivers and Controlling LCD

Learn the architecture of Linux drivers and how to control LCD through this experimental lab. Explore topics such as character device drivers, block device drivers, and network device drivers.

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Understanding Linux Device Drivers and Controlling LCD

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  1. Computer System Laboratory Lab10 Linux Drivers

  2. Experimental Goal LCD Understand the architecture of Linux drivers and learn how to control LCD Lab8

  3. Environment • Host System • Windows XP/Ubuntu 8.04 • Build System • Ubuntu 8.04 • Target System • XScale PXA270 • Software • Linux kernel, please refer to Lab5 • BusyBox, please refer to Lab6 • Creator PXA270 LCD driver, please refer to Lab9 • Also include 8-bit LED lamps, 4-digit 7 segment LED and keypad drivers • You can download all the source codes from • RSWiki CSL Course Software Lab10

  4. Device Drivers • What are the 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 the device driver Lab10

  5. Linux Device Drivers • Why learning Linux driver model? • The rate at which new hardware becomes available (and obsolete!) pguaranteesthat driver writers will be busy for the foreseeable future • Why Linux? • Linux shares the biggest market for embedded systems Lab10

  6. Linux Device Drivers (Cont.) Lab10 • Three fundamental types: • Character device driver • Block device driver • Network device driver • Other types: • USB driver • PCI driver • ……

  7. Writing Linux Drivers User Kernel Device File Device Driver define file_operations register driver (VFS) Virtual Device Driver Hardware implement system calls define chipset header define I/O wrapper functions Physical Device Driver implement chipset control functions • A Linux device driver can be divided into two drivers • Virtual device driver • Physical device driver Lab10

  8. Linking Modules to Linux Lab10

  9. How to Write a Module? • A “hello world” example • Note that the messages in printk will be showed in the kernel, you can use dmesg command to check the messages Lab10

  10. Related Commands in Linux • insmod module.ko • This command is used to insert a module into the kernel • The command is like ld, in that it links any unresolved symbol in the module to the symbol table of the running kernel • Unlike the linker, however, it doesn’t modify the module’s disk file, but rather than in-memory copy • rmmod module_name • This command is used to remove a module from the kernel • The 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 Lab10

  11. Writing Driver - Virtual Device Driver struct file_operations dev_fops = { open: dev_open, read: dev_read write: dev_write, release: dev_release, ioctl: dev_ioctl, }; • int register_chrdev(unsigned int major, const char *name, struct file_operations *fops) • Define file_operations and implement system calls • Register driver (character device) Lab10

  12. Writing Driver - Physical Device Driver #define DATA_PORT (*(volatile char*)(0x10000)) char read_b() { return DATA_PORT; } void write_b(char data) { DATA_PORT = data; } • Hardware dependent • Two common approaches to access hardware, i.e. memory mapped I/O and port I/O • Memory mapped I/O: • Access I/O (port) in the same way as memory is accessed • For example, suppose 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: Lab10

  13. Writing Driver - Physical Device Driver (Cont.) if (check_region(0x378, 1)) { printk("<1>parallelport: cannot reserve 0x378\n"); } else { request_region(0x378, 1, "demo"); } char data=inb(0x378);//Read(in) data form the port 0x378 outb(data, 0x378); //Write(out) data to the port 0x378 release_region(0x378, 1); • 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) • Use the I/O commands • Release I/O port Lab10

  14. Creating Device File • In UNIX and Linux, devices are accessed in the same way as files are accessed • These device files are normally in the /devdirectory • We can create device file by the following command: • % mknod /dev/demo c 60 0 • More details about mknod can be found at: • http://linux.vbird.org/linux_basic/0230filesystem.php#mknod • http://rswiki.csie.org/dokuwiki/_media/courses:100_2:lab10_doc.pdf Lab10

  15. Using Your Driver in Applications #include <stdio.h> int main() { char buf[512]; FILE *fp = fopen("/dev/demo", "w+"); if(fp == NULL) { printf("can't open device!\n"); return 0; } fread(buf, sizeof(buf), 1, fp); fwrite(buf, sizeof(buf), 1, fp); fclose(fp); return 0; } • Open the file /dev/demoand test its read and write functions just like a normal file Lab10

  16. Lab Steps • Please download the driver of Lab9 and modify the LCD driver • Change the major number to 119 • e.g. #define MAJOR_NUM 119 • Change creator-pxa270 driver to module mode in menuconfig • <M> Creator-pxa270 LCD • Implement a new ioctl command to show “hello world” on LCD • Please add lsmod, insmod, rmmod commands in busybox • The commands are under Linux Module Utilities • You need to check the support of 2.6.x Linux Kernels • Do not forget to create the new LCD device file • % mknod /dev/lcd c 119 0 • Please write an application to display string on the LCD Panel, where the string is a command-line argument of the application Lab10

  17. Lab Steps (Cont.) • Please print messages in driver modules when you insert and remove them • Please print messages in driver commands when you access the device • e.g. “open command is issued.” Lab10

  18. Lab Requirement • Show more than one messages on LCD from applications • Show the messages of using the new ioctl command on LCD • Show the messages of accessing the device • Including open, close, write, ioctl, etc. Lab10

  19. Bonus keypad • On PXA270, there is a 4x4 keypad device • In Lab8, we port a tetristo PXA270. Now, we would like to use the keypad to play the tetris • Please modify the driver and tetris to support the keypad • The keypad driver is included in the LCD driver • Please show the number of the key pressed on LCD • For more information about hardware registers, please refer to Create Creator PreSOCes Development Kit User’s Guide, 3.7.4 Lab10

  20. Hints struct file_operations creator_pxa270_lcdtxt_fops = { ... write: creator_pxa270_lcdtxt_write, poll: creator_pxa270_lcdtxt_poll, ... • We can use ioctl() to read data from the keypad in applications • In the LCD driver, you can add poll file operation to support the select function used in the tetris, e.g. • For more information about poll, please refer to Linux Device Drivers 3rd, chapter 6, section “poll and select”, http://lwn.net/images/pdf/LDD3/ • In the tetris, there are three functions related to input from keyboard • tetris/src/input/inp_unixterm.c • readchr(), waitinput_stdin(), init_keybd() • We can replace the keyboard with keypad by modifying the 3 functions above Lab10

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