File Systems in Detail

File Systems in Detail

What is a File System?

A file system is a method for storing and organizing computer files and the data they contain to make it easy to find and access them. File systems may use a data storage device such as a hard disk or CD-ROM and involve maintaining the physical location of the files, they might provide access to data on a file server by acting as clients for a network protocol, or they may be virtual and exist only as an access method for virtual data. It is distinguished from a directory service and registry. More formally, a file system is a special-purpose database for the storage, organization, manipulation, and retrieval of data.

Most file systems make use of an underlying data storage device that offers access to an array of fixed-size blocks, sometimes called sectors, generally a power of 2 in size. The file system software is responsible for organizing these sectors into files and directories, and keeping track of which sectors belong to which file and which are not being used. Most file systems address data in fixed-sized units called "clusters" or "blocks" which contain a certain number of disk sectors. This is the smallest amount of disk space that can be allocated to hold a file.

However, file systems need not make use of a storage device at all. A file system can be used to organize and represent access to any data, whether it be stored or dynamically generated.

File Names Conventions

Whether the file system has an underlying storage device or not, file systems typically have directories which associate file names with files, usually by connecting the file name to an index in a file allocation table of some sort, such as the FAT in a DOS file system, or an inode in a Unix-like file system. Directory structures may be flat, or allow hierarchies where directories may contain subdirectories. In some file systems, file names are structured, with special syntax for filename extensions and version numbers. In others, file names are simple strings, and per-file metadata is stored elsewhere.

Metadata

Other bookkeeping information is typically associated with each file within a file system. The length of the data contained in a file may be stored as the number of blocks allocated for the file or as an exact byte count. The time that the file was last modified may be stored as the file's timestamp. Some file systems also store the file creation time, the time it was last accessed, and the time that the file's meta-data was changed. Other information can include the file's device type, its owner user-ID and group-ID, and its access permission settings.

Arbitrary attributes can be associated on advanced file systems, such as XFS, ext2/ext3, some versions of UFS, and HFS+, using extended file attributes. This feature is implemented in the kernels of Linux, FreeBSD and Mac OS X operating systems, and allows metadata to be associated with the file at the file system level. This, for example, could be the author of a document, the character encoding of a plain-text document, or a checksum.

Hierarchical file systems

The hierarchical file system was an early research interest of Dennis Ritchie of Unix fame; previous implementations were restricted to only a few levels, notably the IBM implementations, even of their early databases like IMS. After the success of Unix, Ritchie extended the file system concept to every object in his later operating system developments, such as Plan 9 and Inferno.

Facilities

Traditional file systems offer facilities to create, move and delete both files and directories. They lack facilities to create additional links to a directory (hard links in Unix), rename parent links, and create bidirectional links to files.

Traditional file systems also offer facilities to truncate, append to, create, move, delete and in-place modify files. They do not offer facilities to prepend to or truncate from the beginning of a file, let alone arbitrary insertion into or deletion from a file. The operations provided are highly asymmetric and lack the generality to be useful in unexpected contexts. For example, interprocess pipes in Unix have to be implemented outside of the file system because the pipes concept does not offer truncation from the beginning of files.
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Types of file systems

File system types can be classified into disk file systems, network file systems and special purpose file systems.

Disk file systems

A disk file system is a file system designed for the storage of files on a data storage device, most commonly a disk drive, which might be directly or indirectly connected to the computer. Examples of disk file systems include FAT [FAT12, FAT16, FAT32, exFAT], NTFS, HFS and HFS+, HPFS, ext2, ext3, ext4, ISO 9660, ODS-5, ZFS and UDF. Some disk file systems are journaling file systems or versioning file systems.

Flash file systems

A flash file system is a file system designed for storing files on flash memory devices. These are becoming more prevalent as the number of mobile devices are increasing, and the capacity of flash memories increase.

While a disk file system can be used on a flash device, this is suboptimal for several reasons:

Erasing blocks: Flash memory blocks have to be explicitly erased before they can be rewritten. The time taken to erase blocks can be significant, thus it is beneficial to erase unused blocks while the device is idle.
Random access: Disk file systems are optimized to avoid disk seeks whenever possible, due to the high cost of seeking. Flash memory devices impose no seek latency.
Wear levelling: Flash memory devices tend to wear out when a single block is repeatedly overwritten; flash file systems are designed to spread out writes evenly.

Database file systems

A new concept for file management is the concept of a database-based file system. Instead of, or in addition to, hierarchical structured management, files are identified by their characteristics, like type of file, topic, author, or similar metadata.

Transactional file systems

Each disk operation may involve changes to a number of different files and disk structures. In many cases, these changes are related, meaning that it is important that they all be executed at the same time. Take for example a bank sending another bank some money electronically. The bank's computer will "send" the transfer instruction to the other bank and also update its own records to indicate the transfer has occurred. If for some reason the computer crashes before it has had a chance to update its own records, then on reset, there will be no record of the transfer but the bank will be missing some money.

Transaction processing introduces the guarantee that at any point while it is running, a transaction can either be finished completely or reverted completely (though not necessarily both at any given point). This means that if there is a crash or power failure, after recovery, the stored state will be consistent.

This type of file system is designed to be fault tolerant, but may incur additional overhead to do so.

Journaling file systems are one technique used to introduce transaction-level consistency to filesystem structures.

Network file systems

A network file system is a file system that acts as a client for a remote file access protocol, providing access to files on a server. Examples of network file systems include clients for the NFS, AFS, SMB protocols, and file-system-like clients for FTP and WebDAV.

Special purpose file systems

A special purpose file system is basically any file system that is not a disk file system or network file system. This includes systems where the files are arranged dynamically by software, intended for such purposes as communication between computer processes or temporary file space.

Special purpose file systems are most commonly used by file-centric operating systems such as Unix. Examples include the procfs (/proc) file system used by some Unix variants, which grants access to information about processes and other operating system features.

Deep space science exploration craft, like Voyager I & II used digital tape-based special file systems. Most modern space exploration craft like Cassini-Huygens used Real-time operating system file systems or RTOS influenced file systems. The Mars Rovers are one such example of an RTOS file system, important in this case because they are implemented in flash memory.

Crash counting is a feature of a file system designed as an alternative to journaling. It is claimed that it maintains consistency across crashes without the code complexity of implementing journaling.

File systems and operating systems

Most operating systems provide a file system, as a file system is an integral part of any modern operating system. Early microcomputer operating systems' only real task was file management — a fact reflected in their names. Some early operating systems had a separate component for handling file systems which was called a disk operating system. On some microcomputers, the disk operating system was loaded separately from the rest of the operating system. On early operating systems, there was usually support for only one, native, unnamed file system; for example, CP/M supports only its own file system, which might be called "CP/M file system" if needed, but which didn't bear any official name at all.

Because of this, there needs to be an interface provided by the operating system software between the user and the file system. This interface can be textual or graphical. If graphical, the metaphor of the folder, containing documents, other files, and nested folders is often used.

Flat file systems

In a flat file system, there are no subdirectories—everything is stored at the same (root) level on the media, be it a hard disk, floppy disk, etc. While simple, this system rapidly becomes inefficient as the number of files grows, and makes it difficult for users to organize data into related groups.

Like many small systems before it, the original Apple Macintosh featured a flat file system, called Macintosh File System. Its version of Mac OS was unusual in that the file management software (Macintosh Finder) created the illusion of a partially hierarchical filing system on top of MFS. This structure meant that every file on a disk had to have a unique name, even if it appeared to be in a separate folder. MFS was quickly replaced with Hierarchical File System, which supported real directories.

A recent addition to the flat file system family is Amazon's S3, a remote storage service, which is intentionally simplistic to allow users the ability to customize how their data is stored. The only constructs are buckets and objects. Advance file management is allowed by being able to use nearly any character including '/' in the objects name, and the ability to select subsets of the bucket's content based on identical prefixes.

File systems under Unix-like operating systems

Unix-like operating systems create a virtual file system, which makes all the files on all the devices appear to exist in a single hierarchy. This means, in those systems, there is one root directory, and every file existing on the system is located under it somewhere. Unix-like systems can use a RAM disk or network shared resource as its root directory.

Unix-like systems assign a device name to each device, but this is not how the files on that device are accessed. Instead, to gain access to files on another device, the operating system must first be informed where in the directory tree those files should appear. This process is called mounting a file system. For example, to access the files on a CD-ROM, one must tell the operating system "Take the file system from this CD-ROM and make it appear under such-and-such directory". The directory given to the operating system is called the mount point - it might, for example, be /media. The /media directory exists on many Unix systems and is intended specifically for use as a mount point for removable media such as CDs, DVDs and like floppy disks. It may be empty, or it may contain subdirectories for mounting individual devices. Generally, only the administrator or root may authorize the mounting of file systems.

File systems under Linux

Linux supports many different file systems, but common choices for the system disk include the ext family such as ext2 and ext3, XFS, JFS and ReiserFS.

File systems under Solaris

The Sun Microsystems Solaris operating system in earlier releases defaulted to UFS for bootable and supplementary file systems. Solaris defaulted to, supported, and extended UFS.
Support for other file systems and significant enhancements were added over time, including Veritas Software Corp. VxFS, Sun Microsystems QFS, Sun Microsystems UFS, and Sun Microsystems ZFS.

Kernel extensions were added to Solaris to allow for bootable Veritas VxFS operation. Logging or Journaling was added to UFS in Sun's Solaris 7. Releases of Solaris 10, Solaris Express, OpenSolaris, and other open source variants of the Solaris operating system later supported bootable ZFS.

Logical Volume Management allows for spanning a file system across multiple devices for the purpose of adding redundancy, capacity, and/or throughput. Legacy environments in Solaris may use Solaris Volume Manager Multiple operating systems may use Veritas Volume Manager. Modern Solaris based operating systems eclipse the need for Volume Management through leveraging virtual storage pools in ZFS.

File systems under Mac OS X

Mac OS X uses a file system that it inherited from classic Mac OS called HFS Plus. HFS Plus is a metadata-rich and case preserving file system. Due to the Unix roots of Mac OS X, Unix permissions were added to HFS Plus. Later versions of HFS Plus added journaling to prevent corruption of the file system structure and introduced a number of optimizations to the allocation algorithms in an attempt to defragment files automatically without requiring an external defragmenter.

Filenames can be up to 255 characters. HFS Plus uses Unicode to store filenames. On Mac OS X, the filetype can come from the type code, stored in file's metadata, or the filename.

HFS Plus has three kinds of links: Unix-style hard links, Unix-style symbolic links and aliases. Aliases are designed to maintain a link to their original file even if they are moved or renamed; they are not interpreted by the file system itself, but by the File Manager code in userland.

Mac OS X also supports the UFS file system, derived from the BSD Unix Fast File System via NeXTSTEP. However, as of Mac OS X 10.5, Mac OS X can no longer be installed on a UFS volume, nor can a pre-Leopard system installed on a UFS volume be upgraded to Leopard.

File systems under Microsoft Windows

Windows makes use of the FAT and NTFS file systems.

The File Allocation Table (FAT) filing system, supported by all versions of Microsoft Windows, was an evolution of that used in Microsoft's earlier operating system. FAT ultimately traces its roots back to the short-lived M-DOS project and Standalone disk BASIC before it. Over the years various features have been added to it, inspired by similar features found on file systems used by operating systems such as Unix.
Older versions of the FAT file system (FAT12 and FAT16) had file name length limits, a limit on the number of entries in the root directory of the file system and had restrictions on the maximum size of FAT-formatted disks or partitions. Specifically, FAT12 and FAT16 had a limit of 8 characters for the file name, and 3 characters for the extension (such as .exe). This is commonly referred to as the 8.3 filename limit. VFAT, which was an extension to FAT12 and FAT16 introduced in Windows NT 3.5 and subsequently included in Windows 95, allowed long file names (LFN). FAT32 also addressed many of the limits in FAT12 and FAT16, but remains limited compared to NTFS.

NTFS, introduced with the Windows NT operating system, allowed ACL-based permission control. Hard links, multiple file streams, attribute indexing, quota tracking, compression and mount-points for other file systems are also supported, though not all these features are well-documented.

Unlike many other operating systems, Windows uses a drive letter abstraction at the user level to distinguish one disk or partition from another. For example, the path C:\WINDOWS represents a directory WINDOWS on the partition represented by the letter C. The C drive is most commonly used for the primary hard disk partition, on which Windows is usually installed and from which it boots. This "tradition" has become so firmly ingrained that bugs came about in older versions of Windows which made assumptions that the drive that the operating system was installed on was C. The tradition of using "C" for the drive letter can be traced to MS-DOS, where the letters A and B were reserved for up to two floppy disk drives. Network drives may also be mapped to drive letters.
Data retrieval process

The operating system calls on the IFS manager. The IFS calls on the correct FSD in order to open the selected file from a choice of four FSDs that work with different storage systems—NTFS, VFAT, CDFS, and Network. The FSD gets the location on the disk for the first cluster of the file from the FAT, FAT32, VFAT, or, in the case of Windows NT based, the MFT. In short, the whole point of the FAT, FAT32, VFAT, or MFT is to map out all the files on the disk and record where they are located.

Introduction to CAN (Controlled Area Network)

Introduction to CAN (Controlled Area Network)

OVERVIEW

CAN was originally developed by the German company, Robert Bosch, for use in cars, to provide a cost-effective communications bus for in-car electronics and as alternative to expensive, cumbersome and unreliable wiring looms and connectors. The car industry continues to use CAN for an increasing number of applications, but because of its proven reliability and robustness, CAN is now also being used in many other control applications.
Intra-vehicular communication:

A typical vehicle has a large number of electronic control systems

The growth of automotive electronics is a result of:
Customers wish for better comfort and better safety.
Government requirements for improved emission control
Reduced fuel consumption

Some of such control systems
Engine timing
Gearbox and carburetor throttle control
Anti-block systems (ABS)
Acceleration skid control (ASC)

The complexity of the functions implemented by these electronic control systems necessitates communication between them.
In addition, a number of systems are being developed which will cover more than one device. For example
ASC requires the interplay of the engine timing and carburetor control in order to reduce torque when drive wheel slippage occurs.
In the electronic gearbox control, the ease of gear changing can be improved by a brief adjustment to ignition timing

How do we connect these control devices?

With conventional systems, data is exchanged by means of dedicated signal lines.

But this is becoming increasingly difficult and expensive as control functions become ever more complex.

In the case of complex control systems in particular, the number of connections cannot be increased much further.

Solution: Use Field bus networks for connecting the control devices

FIELD BUS NETWORKS


Field buses are communication technologies and products used in vehicular, automation and process control industries.

Proprietary Field buses
Proprietary Field buses are an intellectual property of a particular company or body.

Open Field buses
For a Field bus to be Open, it must satisfy the following criteria.
The full Field bus Specification must be published and available at a reasonable price.
Critical ASIC components must be available, also at a reasonable price.
Well defined validation process, open to all of the Field bus users.


Field bus Advantages:

I.Reduces the complexity of the control system in terms of hardware outlay.

II.Resulting in the reduced complexity of the control system, project design engineering is made simpler, more efficient and conversely less expensive.

III.By selecting a recognized and well established system, this will make the Fieldbus equipment in you plant or plants interchangeable between suppliers.

IV.The need to be concerned about connections, compatibility and other potential problems is eradicated.

What constitutes a Field bus?
The specification of a Field bus should ideally cover all of the seven layers of the OSI model as shown below,.

FEATURES OF CAN
CAN features are as follows:-

CAN is a robust protocol – essential for automotive applications
SO 11898 and SAE/J2411 are open standards
Well documented and fully supported worldwide
Choice of three CAN physical layer options
High-speed (HS)for high data rates
Fault-tolerant (FT)for additional robustness
Single-wire (SW)for minimum wiring
Any node can access the bus when the bus is quiet.
Non- destructive bit-wise arbitration to allow 100% use of bandwidth without loss of data.
Variable message priority based on 11-bit (or 29 bit) packet identifier.
Peer- to-Peer and multi-cast reception
Automatic error detection, signaling and retries.
Data packets 8 bytes long

BENEFITS OF CAN

Can is a fast serial Bus that designed to provide
An efficient
Reliable and
Very economical link between sensors & actuators
Can uses a twisted pair cables to communicate at speed up to 1 Mbit/s up to 40 devices.
Originally CAN is developed to simplify the wiring in automobiles.
CAN field buses are now used in machine and factory automation products as well.

CAN HISTORY
In the early 1980s, engineers at Bosch were evaluating existing serial bus systems regarding their possible use in passenger cars. Because none of the available network protocols were able to fulfill the requirements of the automotive engineers, Uwe Kiencke started the development of a new serial bus system in 1983. The new bus protocol was mainly supposed to add new functionality – the reduction of wiring harnesses was just a by-product, but not the driving force behind the development of CAN. Engineers from Mercedes-Benz got involved early on in the specification phase of the new serial bus system, and so did Intel as the potential main semiconductor vendor. Professor Dr. Wolfhard Lawrenz from the University of Applied Science in Braunschweig-Wolfenbüttel, Germany, who had been hired as a consultant, gave the new network protocol the name ‘Controller Area Network’. Professor Dr. Horst Wettstein from the University of Karlsruhe also provided academic assistance. In February of 1986, CAN was born: at the SAE congress in Detroit, the new bus system developed by Bosch was introduced as ‘Automotive Serial Controller Area Network’. Uwe Kiencke, Siegfried Dais and Martin Litschel introduced the multi-master network protocol. It was based on a non-destructive arbitration mechanism, which would grant bus access to the message with the highest priority without any delays. There was no central bus master. Furthermore, the fathers of CAN – the individuals mentioned above plus Bosch employees Wolfgang Borst, Wolfgang Botzenhard, Otto Karl, Helmut Schilling, and Jan Unruh – had implemented several error detection mechanisms. The error handling also included the automatic disconnection of faulty bus nodes in order to keep up the communication between the remaining nodes. The transmitted messages were not identified by the node address of the transmitter or the receiver of the message (as in almost all other bus systems), but rather by their content. The identifier representing the content of the message also had the function of specifying the priority of the message within the system.

A lot of presentations and publications describing this innovative communication protocol followed, until in mid 1987 – two months ahead of schedule – Intel delivered the first CAN controller chip, the 82526. It was the very first hardware implementation of the CAN protocol. In only four years, an idea had become reality. Shortly thereafter, Philips Semiconductors introduced the 82C200. These two earliest ancestors of the CAN controllers were quite different concerning acceptance filtering and message handling. On one hand, the FullCAN concept favored by Intel required less CPU load from the connected micro-controller than the BasicCAN implementation chosen by Philips. On the other hand, the FullCAN device was limited regarding the number of messages that could be received. The BasicCAN controller also required less silicon. In today’s CAN controllers, the ‘grandchildren’, very often different concepts of acceptance filtering and message handling have been implemented in the same module, making the misleading terms BasicCAN and FullCAN obsolete.


IMPLEMENTATION OF CAN

Communication is identical for all implementations of CAN. However, there are two principal hardware implementations. The two implementations are known as Basic CAN and Full CAN.

Basic CAN
In Basic CAN configurations there is a tight link between the CAN controller and the associated microcontroller. The microcontroller, which will have other system related functions to administer, will be interrupted to deal with every CAN message.

Full CAN
Full CAN devices contain additional hardware to provide a message "server" that automatically receives and transmits CAN messages without interrupting the associated microcontroller. Full CAN devices carry out extensive acceptance filtering on incoming messages, service simultaneous requests, and generally reduce the load on the microcontroller.

Network Sizes
The number of nodes that can exist on a single network is, theoretically, limited only by the number of available identifiers. However, the drive capabilities of currently available devices impose greater restrictions. Depending on the device types, up to 32 or 64 nodes per network is normal, but at least one manufacturer now provides devices that will allow networks of 110 nodes.

HOW CAN WORKS ?

Principle

Data messages transmitted from any node on a CAN bus do not contain addresses of either the transmitting node, or of any intended receiving node.
Instead, the content of the message (e.g. Revolutions per Minute, Hopper Full, X-ray Dosage, etc.) is labeled by an identifier that is unique throughout the network. All other nodes on the network receive the message and each performs an acceptance test on the identifier to determine if the message, and thus its content, is relevant to that particular node. If the message is relevant, it will be processed; otherwise it is ignored. The unique identifier also determines the priority of the message. The lower the numerical value of the identifier, the higher the priority.
In situations where two or more nodes attempt to transmit at the same time, a non-destructive arbitration technique guarantees that messages are sent in order of priority and that no messages are lost.

Bit encoding
CAN use Non Return to Zero (NRZ) encoding (with bit-stuffing) for data communication on a differential two wire bus. The use of NRZ encoding ensures compact messages with a minimum number of transitions and high resilience to external disturbance.

The physical bus
The two wire bus is usually a twisted pair (shielded or unshielded). Flat pair (telephone type) cable also performs well but generates more noise itself, and may be more susceptible to external sources of noise.

The CAN protocol is an international standard defined in the ISO 11898. Beside the CAN protocol itself the conformance test for the CAN protocol is defined in the ISO 16845, which guarantees the interchangeability of the CAN chips.


CAN is based on the “broadcast communication mechanism”, which is based on a message-oriented transmission protocol. It defines message contents rather than stations and station addresses. Every message has a message identifier, which is unique within the whole network since it defines content and also the priority of the message. This is important when several stations compete for bus access (bus arbitration), as a result of the content-oriented addressing. This allows for a modular concept and also permits the reception of multiple data and the synchronization of distributed processes. Also, data transmission is not based on the availability of specific types of stations, which allows simple servicing and upgrading of the network.

Message formats

CAN distinguishes four message formats: data, remote, error, and overload frames. Here we limit the discussion to the data frame, shown in Fig. 5. A data frame begins with the start-of-frame (SOF) bit. It is followed by an eleven-bit identifier and the remote transmission request (RTR) bit. The identifier and the RTR bit form the arbitration field. The control field consists of six bits and indicates how many bytes of data follow in the data field. The data field can be zero to eight bytes. The data field is followed by the cyclic redundancy checksum (CRC) field, which enables the receiver to check if the received bit sequence was corrupted. The two-bit acknowledgment (ACK) field is used by the transmitter to receive an acknowledgment of a valid frame from any receiver. The end of a message frame is signalled through a seven-bit end-offrame (EOF). There is also an extended data frame with a twenty-nine-bit identifier (instead of eleven bits).
The CAN protocol was internationally standardized in 1993 as ISO 11898-1. The development of CAN was mainly motivated by the need for new functionality, but it also reduced the need for wiring. The use of CAN in the automotive industry has caused mass production of CAN controllers. Today, CAN controllers are integrated on many microcontrollers and available at a low cost.

CAN ARCHITECTURE

Any node can access the bus when the bus is quiet

Non-destructive bit-wise arbitration to allow 100% use of the bandwidth without loss of data

Variable message priority based on 11-bit (or 29 bit) packet identifier

Peer-to-peer and multi-cast reception

Automatic error detection, signalling and retries

Data packets 8 bytes long


ERROR HANDLING PERFORMANCE OF CAN

Error detection and error handling are important for the performance of CAN. Because of complementary error detection mechanisms, the probability of having an undetected error is very small. Error detection is done in five different Vehicle Applications of Controller Area Network 7 ways in CAN: bit monitoring and bit stuffing, as well as frame check, ACK check, and CRC. Bit monitoring simply means that each transmitter monitors the bus level, and signals a bit error if the level does not agree with the transmitted signal. (Bit monitoring is not done during the arbitration phase.) After having transmitted five identical bits, a node will always transmit the opposite bit. This extra bit is neglected by the receiver. The procedure is called bit stuffing, and it can be used to detect errors. The frame check consists of checking that the fixed bits of the frame have the values they are supposed to have, e.g., EOF consists of seven recessive bits. During the ACK in the message frame, all receivers are supposed to send a dominant level. If the transmitter, which transmits a recessive level, does not detect the dominant level, then an error is signalled by the ACK check mechanism. Finally, the CRC is that every receiver calculates a checksum based on the message and compares it with the CRC field of the message. Every receiver node obviously tries to detect errors within each message. If an error is detected, it leads to an immediate and automatic retransmission of the incorrect message. In comparison to other network protocols, this mechanism leads to high data integrity and a short error recovery time. CAN thus provides elaborate procedure for error handling, including retransmission and reinitialization. The procedures have to be studied carefully for each application to ensure that the automated error handling is in line with the system requirements.

APPLICATIONS

CAN networks can be used as an embedded communication system for microcontrollers as well as an open communication system for intelligent devices. The CAN serial bus system, originally developed for use in automobiles, is increasingly being used in industrial field bus systems, the similarities are remarkable. In both cases some of the major requirements are: low cost, the ability to function in a difficult electrical environment, a high degree of real-time capability and ease of use.
Some users, for example in the field of medical engineering, opted for CAN because they have to meet particularly stringent safety requirements. Similar problems are faced by manufacturers of other equipment with very high safety or reliability requirements (e. g. robots, lifts and transportation systems). CAN controllers and interface chips are physically small. They are available as low-cost, off-the-shelf components. They will operate at high, real-time speeds, and in harsh environments. All these properties have led to CAN also being used in a wide range of applications other than the car industry. The benefits of reduced cost and improved reliability that the car industry gains by using CAN are now available to manufacturers of a wide range of products.

For example:

• Marine control and navigation systems
• Elevator control systems
• Agricultural machinery
• Production line control systems
• Machine tools
• large optical telescopes
• Photo copiers
• Medical systems
• Paper making and processing machinery

VEHICLE APPLICATIONS OF CAN

The Controller Area Network (CAN) is a serial bus communications protocol developed by Bosch in the early 1980s. It defines a standard for efficient and reliable communication between sensor, actuator, controller, and other nodes in real-time applications. CAN is the de facto standard in a large variety of networked embedded control systems. The early CAN development was mainly supported by the vehicle industry: CAN is found in a variety of passenger cars, trucks, boats, spacecraft, and other types of vehicles. The protocol is also widely used today in industrial automation and other areas of networked embedded control, with applications in diverse products such as production machinery, medical equipment, building automation, weaving machines & wheelchairs.
In the automotive industry, embedded control has grown from stand-alone systems to highly integrated and networked control systems. By networking electro-mechanical subsystems, it becomes possible to modularize functionalities and hardware, which facilitates reuse and adds capabilities. Fig. 1 shows an example of an electronic control unit (ECU) mounted on a diesel engine of a Scania truck. The ECU handles the control of engine, turbofan, etc. but also the CAN communication. Combining networks and mechatronic modules makes it possible to reduce both the cabling and the number. The work of K. H. Johansson was partially supported by the European Commission through the ARTIST2 Network of Excellence on Embedded Systems Design, by the Swedish Research Council, and by the Swedish Foundation for Strategic Research through an Individual Grant for the Advancement of Research Leaders.


The work of M. T¨orngren was partially supported by the European Commission through ARTIST2 and by the Swedish Foundation for Strategic Research through the project SAVE of connectors, which facilitates production and increases reliability. Introducing networks in vehicles also makes it possible to more efficiently carry out diagnostics and to coordinate the operation of the separate subsystems.

Heavy Vehicles

Most existing vehicle model libraries are designed primarily for cars. Heavy vehicles have a number of sub-systems which are not present in passenger cars. Particularly the engine/transmission system includes de-vices like an exhaust brake and possibly a retarder. Further, the cooling system also has a more prominent role than in cars, and coolant is often used both by the engine and the transmission.

Signalling Bus

A key issue in an architecture which contains both physical plant and controller models is the handling of electrical signals. The controllers need to exchange data among themselves and they need to exchange signals with sensors and actuators. For our applications the actual signalling behaviour is not that important, an ideal communications model is sufficient. For the communication between a plant and its controller, standard library in-ports and out-ports are used. The communication between the controllers was a tougher case. Two implementations of the same controller may not have the same signalling needs, thus it must be possible to change the set of signals sent between control units. Separate input and output ports for all links between control units in the vehicle would create an un-decipherable graphical mess. Some type of signalling bus is needed. Both the standard library bus connectors and the type of bus used in the vehicle modelling architecture proposal by Tiller Etal were evaluated. We did not find enough information about the inter-controller communication in the Tiller paper to implement that system. Our main problem was to find a way of having compatible connectors in all controllers, without modifying the code of every controller when a signal was added to the bus. The standard library bus does not solve that problem, since it requires all signals to be declared in the connector. Eventually we chose a simpler solution based on a common connector called ”CAN” with a replace-able variable, called ”protocol”, which contains all the signals. The protocol variable can easily be redeclared into a type which contains exactly the signals broad-cast on the bus in a particular model. Different implementations of the CAN connector are used for different signal buses in the vehicle.

Most of our control units are implemented through external function calls, thus the drawback of having no convenient graphical way of converting a signal from inport/ outport to bus format is minor.

RESUME

RESUME

Resume is the first step of marketing program for an educated person. Resume is a French word which means ‘To summarise. It is the same as the bio-data, curriculum vitae. It represents a qualified person with all the details. Although you are well qualified and intelligent enough, if your resume in weak, you may not face an interview.

Therefore a good resume is a powerful tool to secure a job. Resume should portray you in the best possible manner. Resume is an important contact with an employer. Usually, a resume consists of two-three typed pages about the candidate.

Contents of Resume:
Resume should contain the most important and a lot of different information, as given here under
1. Personal data (Including Name, Address, Phone no., e-Mail ID, etc.)
2. Educational qualification.
3. Caste and sub caste.
4. Work experience, if any.
5. Other qualifications (Awards, Honours and publications etc.)
6. Sports and other interests.
7. Languages known.
8. Marital status.

Types of Resumes:
There are three kinds of resumes, namely:
1. A Traditional resume.
2. A Functional resume.
3. A Skills Emphasis resume.


1.A Traditional Resume:

This gives the clear list of the candidate’s educational qualification and work experience in the chronological order. It gives the clear information of the job titles, name of the company, school or colleges, dates of enrolment and employment etc., which are essentially needed for the employers. Some professions, viz Law, Finance and IT require such traditional resumes.

The traditional resume should contain the following points
• Continuity in work history
• If you are looking for a job, related to your cost experience
• A gap in past service
• Emphasis on no professional jobs

This traditional resume is not meant for class IV and below grade appointments.

2.A Functional Resume:

This resume contains even minor observations which are not preferable in traditional resume. It highlights your education and job experience and arranges them in a concise manner. It gives more importance to description of functions instead of employment, job titles, names of the company and dates of the employment. This contains the description about the functions which gives the satisfaction and your research. It also contains the way you interact and manage the people and solve the problems.

A functional resume must be existing and personal. Here you can mention abot sports and other extracurricular activities.
A functional resume is preferred in the following context.
1. Change in career
2. With other job oriented experiences, entering the job market with no work history.
3. Returning to the job market after a long gap.
4. Seeking a position unrelated to your previous employment.
5. Promotion from one position to another


3. A Skills Emphasis Resume
In format, this resembles a functional resume. It gives importance to identification. E.g.: Desired: Experience as a sales representative, leadership quality, communication skills, financial analysis and creativity etc.

ORAL COMMUNICATION ACTIVITIES

ORAL COMMUNICATION ACTIVITIES

Dyadic Communication
The term “dyadic communication” is general reference to an interaction between two persons. Even if more than two persons are present in a situation, it is only two communications that play fundamental role. The formal dyadic communication with which we are concerned demands artistry that can be acquired through practice, dyadic communication may take a number of forms but we shall discuss only the following file, face to face conversation, telephonic conversation, interview, inspection and dictation.

Face to face conversation:
Conversation is the most common form of dyadic communication. It links people together to be in social or personal life. Conversation may be defined as oral and usual informal or friendly exchange of views, ideas etc. In a conversation the participants has to play the role of a speaker or a listener interchangeable the role that the best practice for conversation itself holds true.

Helpful hints for successful face to face conversation
1. The conversation should be of interest to the participant and may being with a topic in which both have some interest. As it flow into new channels adjusts yourself to be comments and new point of view this needs not bother you because often during this spells new thoughts are generated.
2. Be alert to the attitudes that others may have and don’t be surprised when you realise that the attitudes are likely to change.
3. Occasionally call the person by name and look at him while speaking, if you speak the name aloud you would be generating a more friendly feeling to cop it all take care of a language and oral demeanour.
4. Be always courteous and cheerful. Feel interested in what is being said.
5. Being dogmatic and argumentative may spoil your conversation. But it is useful to have a point of view.
6. Avoid pet and superfluous words and phrases

Telephonic Conversation:
One form of dyadic conversation is interaction between two persons on a telephone. In this form the advantage of using body language and eye contact is lost. But it is one of the common and fastest ways of contacting persons. It is simple handy in the long run economically, therefore it is termed as prices less means of communication.

Guidelines for telephonic conversation:
1. Cultivate a cheerful and friendly tone.
2. Modulate your voice.
3. Never sound hurried, flustered or impotence.
4. Pronunciate your words clearly.
5. Do not use slang.
6. Speak distinctly if you use a word which is likely to be misunderstood, spell it out.
7. Listen attentively to the caller.
8. Be courteous in all the circumstances.
9. Don’t engage your telephone longer than necessary.

While receiving and making calls bare the following points in mind:

Lift the receiver promptly.
Reveal your identity
Obtain the caller’s name and designation
Give the required information accurately
Keep a job pad and pencil, Handy to note message
While calling keep all the materials ready before you dial the number

Telephone is the best answer to transact with an officer busy interacting with others.

Interviews
The word “Interview” is derived from interview meaning sight between. It is a meeting between two persons with a specific purpose. An interview demands direct and dynamic interaction. One of the purposes of interview is to elicit information, which is not available from written records or other sources.

Therefore various steps of interviews ranging from the one conducted by a journalist for a newspaper reporting to that by a psychiatrists with a patient. The purpose defines the type of interview. Here we are interested in the following two types of interviews :

1. Employment interviews
2. Data collection interviews

The term employment interview refers to interviews of a candidate for a job in a particular organisation. Promotional interview and annual interviews are conducted in respect of the employees who are already in service.

Employment Interview:
The main purpose of the employer is to judge the stability of applicant to the job and that of the applicant to find out whether the needs and requirements of the job wood suit him also whether the environment to his professional growth and intellectual or social pursuits.

Disposition:
A vital piece of information that the employer would like to have is whether the candidate has the ability to work with others.

Circumstances:
A peep into the interview’s previous environment and family circumstances may give some clue to the candidate capacity to work.

Data Collection Interview:
Very often one would be called upon to collect data for specific purpose and present it in the form of a letter, memo, report etc. This information may either be available with your officers in your own organisation or other organisation.

Instructions:
Directing others to perform a particular function of a profession infant giving instructions in an art can be cultivated. While giving instructions to sub-ordinates and junior officers the following things must be keep in mind:
1. The background knowledge of the recipient.
2. His physiological recipient.
3. His capacity to group.
4. His ability to act upon your instruction.

Dictation:
Dictation is another type of communication very frequently used in professional organisation. It is an art in which every profess prospective employers main aim is to judge your sense of values, your attitude towards the work.

Each applicant must plan to be successful. Failure in interview certainly injures the ego of a person temporarily. So to be successful must pay the close attention to the following:
1. Physical appearance creates the first impression and tells something about the personality of the individual.
2. Good department and good manners generates a proper atmosphere and put you at ease, nothing should appear to be artificial and imitative.
3. Care should be taken not to in judge in certain mannerism in speech and behaviour.
4. Does not use long and highly colloquial long wage the tone should be friendly but not imitative.
5. One must be careful not be in the habit of making add gestures while taking.
6. Listening is an art one should create an impression that he is a good listener.
7. Speech must be cultivated by listening to recordings one’s own voice to get job and to move up on the ladder of career.
8. Most important of all these is to be clear doubts and those thoughts must be expressed in plain language.
9. Avoid giving uncomplimentary references to your former employers.

Employer’s expectations:
We may classify the information which an employer seeks while considering a person for job into the following sub-headings.

State of Health:
Every organisation desires its employees to be in a healthy state. A part from judge at the interview the organisation requires a new entrant to undergo a medical examination the standards of which differ from profession to profession.

Attainments:
A probe is made through searching question to verify what the candidate in the bio-data writes and to asset nature and quality of his achievements.

Intelligence:
A close observation is made of the reflex and response of the interview to discover the extent of his grasp and confidence.

Attitude:
Certain questions are directed merely to find out the candidate’s attitude for the job he has applied for.

Interests:
An attempt is made to understand the other dimensions of the responsibility of the candidate by encouraging him to speak about his day today business. Some of the hints given below would prove helpful to you in learning the art of dictation.
1. Tell the steno the form of communication you are going to use and the situation promoting it.
2. Picture the entire composition i.e. the total matter to be dictated in verbal terms.
3. Take care in dictating homonyms. E.g., pale, pail, ascent compliment, etc.
4. Dictating all the punctuation marks.
5. Match the speech of dictation to the speed of your steno.
6. If you dictate into a machine listen to the material recoded before asking your steno to type it. This should be also with a steno new to the job.

Meetings:
The word meeting is used in two sense; one to refer to a small group meeting committee, meeting of board of directors, cabinet meeting, meeting of sectional heads etc. And the second to refer to any meet of two or more persons, what ever be the label application to such a group, the meeting is perhaps the most commonly used form of discussion in a professional organisation. The person who chairs the meeting act is the leader of the groups and usually has a higher status or enjoys authority over other members. Every meeting is result oriented and therefore the discussion is directed towards a specific end.

Purpose:
There are number of purpose for which meeting are held, some of the following are typical of most situations.
1. To save time and communication.
2. To convey information to a group at one time.
3. To brief members on plans already made or work already done.
4. To give and get new ideas.
5. To get immediate reactions, a new ideas, proposals and pans.
6. To exchange ideas and experience.
7. To discuss and solve problems.
8. To resolve conflict confusions and disagreements.
9. To arrive at widely acceptable decisions persons in power to take decisions.

Chairmanship:
The chairman generally concerns a meeting of the member of a committee or any other constituted body or a member authorised by him. In other cases an authorised official calls it whose wishes to use it for any other purpose mentioned earlier.
In this case he acts as the chairman and he may name a member of group to act as a secretary of a particular meeting. The following points should be born in mind by the person who calls the meeting:
1. The announcement for any meeting must be made in written at least a week before the fixed date.
2. The notice should be sent to all members, even if it were known that some of them would not attend.
3. The notice should clearly state the agenda.

Chairmanship:
Chairing a meeting requires a lot of patience, a sense of humour and sound knowledge of the technique of making people discuss a meeting intelligently and arrive at well reasoned conclusion, when you are called upon to conduct a meeting read through the agenda carefully and prepare a discussion plan. Before the meeting begins ensure that the proper physical arrangement has been made and aids and materials to be used are available at the venue.

A discussion plan is nothing but a guide prepared by you reflecting your own thinking and the subject to be discussed. A logical sequence of the ideas is expected to be presented. The questions likely to be raised to the members and the conclusions that might be reached you should also estimate the time you should like to be devoted to each item in the agenda.

In every meeting the beginning is crucial; don’t wait for those who are not present, think of those who are present. After you have set the discussion in motion invited response but don’t get unnerved if there is silence for some time. Do not rush the group at arrive at a discussion. Let the meeting problem entered and discussion oriented. Give a fair chance to every member to speak and don’t take sides. Be especially alert about problem participant, the commenter and monopolizes and the reticent.

The conclusion of the meeting put special responsibility on the chairman. As chairman’s duty is to take a position of the authority and to state firmly, the result of the discussion are namely to obtain the maximum benefits, the summary and closing of the meeting are of equal importance.
To sum up the chairman performs the following functions which are necessary:
1. He draws preliminary plans and makes the arrangements for the meeting.
2. He invites, directs and controls the discussion.
3. He facilitates or directs the plan of action for implementing the conclusions.

Participation:
The role of participant is an equally important aspect of a meeting which very much depends upon the kind and quality of contribution made by the participants, when you are asked to attend a meeting and to go through the agenda, carefully collect the useful information and develop a tentative point of view with an open mind.
Be a good listener and try to read the thoughts behind the expression, whether relevant or not to listen to every speaker attentively. Don’t hesitate to volunteer and relevant information you may have on the topic under discussion and with confidence. Sincere participation should be your goal. Note down the important points briefly at the meeting for reference in future physical arrangements.

A good physical arrangement contribution to the success of the meeting is the most favourable seating arrangement is around a large table.

In case of rectangular table is used the chairman should seat himself at a position from where he can face everyone.

Group Discussion:
The term group discussion is used to refer to a situation in which a small number of persons meet face to face and through free oral interaction among themselves, exchange information or attempt to reach a decision on shared problem if it is difficult to specify the number of participants that would make the group discussion useful. Research indicates that if the number is kept between 5 to 9, fruitful discussion can take place. It is also observed that group of even numbers of participants tend to be less stable and rewarding the groups. As the discussion precedes one of the participants emerged as a leader. One of the advantages of this type of discussion is that there is a self imposed discipline on the discussion and greater responsibility on the participants for making it useful to keep the discussion on the track it may be worthwhile for a participant to summarise the point.

Occasionally when the group discussion takes place some persons may be invited as observer that may be done for two purposes.
1. To let the observer learn the process of group discussion and
2. To evaluate the contribution by members purpose.

Very often group discussion is used in addition to written test/interviews for employment. Therefore a representative of the prospective will judge each individual’s personality traits such as intellectual ability, creativity approach to solve problems, qualities of leadership, tolerance and group behaviour. In this process he would also note the clarity of thought and felicity of expression of each member.

Sometimes a group discussion is also an instrument to develop and judge the student personality trails mentioned above. It trails the student to function in the professional world efficiently.

Organisation:
There are two ways of organising a group discussion.
1. The topic is announced before hand and participant is expected their homework before coming to the discussion table.
2. The topic is announced after the members have assembled and five to ten minutes are given to them for collecting their thoughts.

The room where the group discussion takes place should have proper ventilation and sufficient height. The chairs should be arranged in a circle so that a member’s expression can be seeing all by others.

Case-study:
Case –study means analysing a case subject to a problem. Every now and then in a day to day life we come across crisis, problem, etc which might have multi dimensional solution which might vary from one person’s perception to another person’s perception. Choosing the ability of the person analysing the case the detailed study performed would only make it possible to find the most feasible solution.