Embedded system - embedded system programming

Embedded system - embedded system programming

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  Embedded System Programming Introduction toDevice Drivers By :- Vibrant Technologies & Computer
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  What are devicedrivers? • 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
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  Types of devicedriver • 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
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  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
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  Character Device Drivers •Data is a serial stream • No random access • Even a block devices can be a character one! – Printers
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  Block Devices • Datais 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
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  Network Interfaces • Networkinterfaces 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
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  Character & BlockDevice 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
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  Loadable modules • Historicallythere 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
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  Kernel Modules • Theprovision 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.
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  Module programming • The2.6 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.
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  Module programs • Requiresheader 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"); }
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  Using macros • Useof 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);
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  Features of kernelprogramming • 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
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