An introduction to USB

In 1994, an alliance of four industrial partners (Compaq, Intel, Microsoft, and NEC) started specifying the USB protocol. The original goal of the protocol was to connect the PC to the telephone and to provide I/O interfaces that were easy to expand and reconfigure. In January 1996, the first version of the USB specification was released, and a subsequent revision (version 1.1) was released in September 1998. The specification allowed 127 devices to be connected together at the same time, with the total communication bandwidth limited to 12 Mbps. Later on, three more members (Hewlett-Packard, Lucent, and Philips) joined the alliance. In April 2000, version 2.0 of the USB specification, which supports transfer rates up to 480 Mbps, was released. Today, USB plays a key role in high-speed (video, imaging, storage) and full-speed (audio, broadband, microphone) data-transfer applications. It also connects a variety of low-speed devices (keyboards, mice, game peripherals, virtual reality peripherals) to the PC.

The USB protocol is strictly hierarchical. In any USB system there is only a single host, and the USB interface to the host computer is referred to as the host controller. There are two standards for host controllers -- the Open Host Controller Interface (OHCI, by Compaq) and the Universal Host Controller Interface (UHCI, by Intel). Both standards provide the same capabilities and work with all USB devices; the hardware implementation of a UHCI is simpler, but requires a more complex device driver (and thus puts more load onto the CPU).

The USB physical interconnect is a tiered star topology, with up to seven tiers. A hub is at the center of each star, and the USB host is considered the root hub. Each wired segment is a point-to-point connection between a hub and USB device; the latter can be either another hub that provides additional attachment points to the system, or a device of some sort that provides functional capabilities. The host uses a master/subordinate protocol to communicate with the USB devices. This approach solves the problem of packet collision but also prevents the attached devices from establishing direct communication with each other.

All the data transfers are initiated by the host controller. Data directed from the host to a device is called downstream or out transfer; data directed from a device to the host is called upstream or in transfer. Data transfer occurs between the host and a particular endpoint on the USB device, and the data link between the host and the endpoint is called a pipe. A given USB device may have many endpoints, and the number of data pipes between the host and the device is the same as the number of endpoints on the device. A pipe may be uni-directional or bi-directional, and the data flow in one pipe is independent of the data flow in any other pipes.

Communication on the USB network can use any one of four different data transfer types:

* Control transfers: These are short data packets for device control and configuration, particularly at attach time.
* Bulk transfers: These are data packets in relatively large quantities. Devices like scanners or SCSI adapters use this transfer type.
* Interrupt transfers: These are data packets that are polled periodically. The host controller will automatically post an interrupt at a specified interval.
* Isochronous transfers: These are data streams in real time with higher requirements for bandwidth than for reliability. Audio and video devices generally use this transfer type.

Like a serial port, each USB port on a computer is assigned a unique identification number (port ID) by the USB controller. When a USB device is attached to a USB port, this unique port ID is assigned to the device and the device descriptor is read by the USB controller The device descriptor includes information that applies globally to the device, as well as information on the configuration of the device. A configuration defines the functionality and I/O behavior of a USB device. A USB device may have one or more configurations, which are described by their corresponding configuration descriptors. Each configuration has one or more interfaces, which can be considered as a physical communication channel; each interface has zero or more endpoints, which can be either data providers or data consumers, or both. Interfaces are described by interface descriptors, and endpoints are described by end-point descriptors. Furthermore, a USB device might also have string descriptors to provide additional information such as vendor name, device name, or serial numbers.

Post Source

http://www.ibm.com/developerworks/linux/library/j-usb.html

Second year microprocessor presentation

A new search engine - CUIL

A new search engine has been launched at the internet - cuil by name. As the first glance it seems to me nice to search on it and it is as fast as google search engine.

For more information read cuil

Public Universities of Bangladesh

Though Bangladesh is a small country but it has large population.Now-a-days a lot of students in Bangladesh are trying to take higher education in different universities. Approximately there are 26 public universities in Bangladesh. The number is not enough to serve the ever growing demand. So many private universities are opened at the same time. But if you concern about quality education i can definitely say that,they are cent percent fail to give it. Now private universities are the place to earn money for the teachers and give money for the students. So education is just like business here.

It is very much unfortunate that many propaganda have been made against public universities. I think this is also a part of business of private universities. Public universities have also many problems. But the concern authority don't find time to solve the problems.

List of public universities of Bangladesh
List of private universities of Bangladesh

Movie Title in Bangla

I am now working to make the English subtitle of A Space Odyssey into Bangla. This is an interesting task for me. This will take a week to complete. After that I will publish it for all Bangla speaking user.

My Favorite Two ScreenSaver

A screen saver is a type of computer program initially designed to prevent "Phosphor burn-in" on CRT and plasma computer monitors by blanking the screen or filling it with moving images or patterns when the computer is not in use. Today, screen savers are also used for entertainment or security purposes.

Here I want to give two of my favorite screen saver. One is from cricinfo about Bangladesh cricket team and another one is from new7wonders about 7wonders.

Click the image to download.

    

You can download the zip file from the link

International Mobile Equipment Identity(IMEI Number)

The International Mobile Equipment Identity or IMEI is a number unique to every GSM and UMTS mobile phone as well as some satellite phones. It is usually found printed on the phone underneath the battery.

The IMEI number is used by the GSM network to identify valid devices and therefore can be used to stop a stolen phone from accessing the network. For example, if a mobile phone is stolen, the owner can call his or her network provider and instruct them to "ban" the phone using its IMEI number. This renders the phone useless, regardless of whether the phone's SIM is changed.

The International Mobile Equipment Identity - a unique 15-digit code used to identify an individual GSM mobile telephone to a mobile network. It can be displayed on most phones by dialling *#06#. It is also usually printed on the compliance plate under the battery.

Prior to April 1st 2004 the numerical format of the code was:
111111-22-333333-4

TAC

FAC

SNR

CD

D14

D13

D12

D11

D10

D09

D08

D07

D06

D05

D04

D03

D02

D01

• TAC: Type Approval Code
• FAC: Final Assembly Code
• SNR: Serial Number
• CD: Check Digit

The first six digits are the TAC (Type Approval Code), which identifies the country where type approval was sought for the phone, as well as the approval number. NOTE: since the 1st April 2004 the TAC will be the abbreviation for Type Allocation Code.

The FAC (Final Assembly Code) identifies the company that produced the mobile phone (eg: SonyEricsson or Nokia). NOTE: From 1st January 2003 a new code allocation procedure has been in place. The changes relate to the format - the Final Assembly Code (FAC) is obsolete and is set to 00 for the period from 1st January 2003 until 1st April 2004. The FAC is now obsolete, and the TAC is now eight instead of six digits, as follows: 11111111-222222-3

TAC

SNR

CD

D14

D13

D12

D11

D10

D09

D08

D07

D06

D05

D04

D03

D02

D01

The 6 digit SNR (Serial Number) has been uniquely assigned to the specific type of handset. The CD (Check Digit) is used to check the code for its validity for Phase 2 and Phase 2+ handsets. Phase 1 GSM handsets, however, always have zero ("0") as check digit.

IMEISV (International Mobile Equipment Identity and Software Version number) is also sometimes used. It offers the possibility of adding the handset's original software version number. It adds a two digit SVN (Software Version Number) at the end of the code, so the numerical format is:
111111-22-333333-4-55, which changed to 11111111-222222-3-44 on 1st April 2004.

---> Analysis of IMEI numbers

Post Source:

http://en.wikipedia.org/wiki/International_Mobile_Equipment_Identity

http://www.orate.co.uk/Mobiles/imei.html

http://www.numberingplans.com/?page=analysis&sub=imeinr

Earthquake at Dhaka, Bangladesh

Last Sunday at 00:52 AM there was an earthquake at Dhaka, Bangladesh. I was at that time preparing for sleep. Suddenly I feel that my bed was moving back and forth for few seconds. The earthquake is not so strong. It has the strength 5.6 at richter scale. Around 20 peoples are injured at Dhaka University.

A New Computer Virus

I have to printout a document from my department yesterday and when I try to use my flash drive(pen drive) today I found a new virus. This is called "1yl2d.bat". I have searched about this virus and found interesting info. This virus was first seen at 15 July in Saudi Arabia. Now it spreads in Bangladesh and those who are not careful be caught with this nasty virus. So be careful about your removable device.

For more read click the link

Just Install Ubuntu

I have ordered Ubuntu 8.04 last month and yesterday I got it. I have installed it in my desktop. I am satisfied with the facilities and graphics provided by Ubuntu. Fast and efficient. Good looking face. And many more...

Thanks Ubuntu. Ooh, Ubuntu is not shipped with audio and video support for windows file format. So I have downloaded VLC player to listen my favorite music as well as seeing videos.