This presentation is about - embedded system programming, What are device drivers?, Types of device driver, Recognizing device drivers, Character Device Drivers, Features of kernel programming,

2. Embedded System
Programming
Introduction to Device Drivers
By :- Vibrant Technologies &
Computer

3. What are device drivers?
• Software interfaces to hardware resources in the
kernel
– Mirrors variety of hardware resources
– Can change constantly
– Will require reconfiguration
– Different interfaces into the same devices
– Require kernel resident programs
– Uses module interface

4. Types of device driver
• There are some general types or characteristics of
device drivers
– Character devices
• Serial data stream
– Block devices
• Accessed via blocked data stream
– Network interfaces
• Although serial, has no mapping into file system

5. Recognising device drivers
• Apart from network devices most drivers
appear like file in the Unix system
• ls –l /dev
– crw-r--r-- 1 root root 10, 134 Jun7 1996 apm_bios
– brw-rw---- 1 root floppy 2, 0 May 14 1996 fd0
Device
type
Major
number
Minor
number
File
Name

6. Character Device Drivers
• Data is a serial stream
• No random access
• Even a block devices can be a character one!
– Printers

7. Block Devices
• Data is read in blocks
• Block size depends upon the device
• Random access is supported
• Files systems can only be mounted block devices
• Block devices can have character interfaces
– fsck works on character “raw” interface to file
system

8. Network Interfaces
• Network interfaces act in some ways like a serial
character orientated device, however they don’t exist
in the file system
• For example eth0 is queried through the ifconfig
command
• Weirdly, network devices can support block features
for example network mounted file systems

9. Character & Block Device number assignment
• Character devices
– 1 Memory
– 4 Terminal
– 6 Parallel interfaces
– 7 Vitual consoles
– 9 SCSI tapes
– 10 Bus mice
– 12 QIC02 Tape
– 13 PC speaker driver
• Block devices
– 1 RAM disk
– 2 Floppy disk
– 3 IDE disk
– 8 SCSI disk
– 11 SCSI CD-ROM
– 13XT 8-bit hard disk

10. Loadable modules
• Historically there has been a split between monolithic kernels
– All code is contained in the kernel, fixed at build or boot time
• This means that kernel can be fast and efficient
• And Micro kernels
– Small lightweight kernel that load features in at run time, when
required
• The kernel is smaller, easier to port, the feaure list of more
flexible
• Linux loadable modules gives a compromise position
– Mainly monolithic kernel but can load modules in when needed
– The use of modules for devices is clearly important

11. Kernel Modules
• The provision of kernel modules allows code to be
introduced into a running kernel.
• This requires the kernel to be built with this capability,
it also requires the commands
– Insmod and rmmod (plus lsmod, depmod and
modprobe)
• Modules can be loaded on demand automatically.

12. Module programming
• The 2.6 kernel has changed the way module
programming is handled.
– We will look at this later on – for the moment we will
deal with 2.4
• Modules under 2.4 are just ordinary unlinked object
files (cc –o)
– Although they must link with the kernel and can
bring it down, so they are rather special.

13. Module programs
• Requires header files
– These will include
others
• Needs an init_module
and cleanup_module
function
• The return value is
important
– Only return 0.
• Use of printk
#include <linux/module.h>
#include <linux/kernel.h>
int init_module(void)
{
printk("<1>Hello world 1.n");
return 0;
}
void cleanup_module(void)
{
printk("KERN_ALERT "Goodbye
cruel world 1.n");
}

14. Using macros
• Use of init &
exit macros
• Use of __init
and __initdata
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>
static int hello_data __init_data= 47;
static int __init hello2_init(void)
{
printk("<1>Hello world 2. %d n", hello_data);
return 0;
}
static void __exit hello2_exit(void)
{
printk("KERN_ALERT "Goodbye cruel world 2.n");
}
module_init(hello2_init);
module_exit(hello2_exit);

15. Features of kernel programming
• Don’t use libraries – only kernel code
– Printk not printf
• Set use of headers
– /usr/include/asm & /usr/include/linux
• Beware of namespace pollution
– Code shares names with the kernel
– Use static

16. ThankThank You !!!You !!!
For More Information click below link:
Follow Us on:
http://vibranttechnologies.co.in/embedded-system-classes-in-
mumbai.html