The Pipe Concept in USB transaction

[senthilnathan.rajesh]

Hi...

Please explain the concept of Pipes in USB Transaction..... Please suggest a good book to know/learn USB Specs and Architecture...

Thanks

 

[alzomor]

books on usb

Hi

Endpoints

Endpoints can be described as sources or sinks of data. As the bus is host centric, endpoints occur at the end of the communications channel at the USB function. At the software layer, your device driver may send a packet to your devices EP1 for example. As the data is flowing out from the host, it will end up in the EP1 OUT buffer. Your firmware will then at its leisure read this data. If it wants to return data, the function cannot simply write to the bus as the bus is controlled by the host. Therefore it writes data to EP1 IN which sits in the buffer until such time when the host sends a IN packet to that endpoint requesting the data. Endpoints can also be seen as the interface between the hardware of the function device and the firmware running on the function device.

All devices must support endpoint zero. This is the endpoint which receives all of the devices control and status requests during enumeration and throughout the duration while the device is operational on the bus.
Pipes

While the device sends and receives data on a series of endpoints, the client software transfers data through pipes. A pipe is a logical connection between the host and endpoint(s). Pipes will also have a set of parameters associated with them such as how much bandwidth is allocated to it, what transfer type (Control, Bulk, Iso or Interrupt) it uses, a direction of data flow and maximum packet/buffer sizes. For example the default pipe is a bi-directional pipe made up of endpoint zero in and endpoint zero out with a control transfer type.

USB defines two types of pipes

* Stream Pipes have no defined USB format, that is you can send any type of data down a stream pipe and can retrieve the data out the other end. Data flows sequentially and has a pre-defined direction, either in or out. Stream pipes will support bulk, isochronous and interrupt transfer types. Stream pipes can either be controlled by the host or device.


* Message Pipes have a defined USB format. They are host controlled, which are initiated by a request sent from the host. Data is then transferred in the desired direction, dictated by the request. Therefore message pipes allow data to flow in both directions but will only support control transfers.



You can also check the usb specification for more info
http://www.usb.org/developers/docs/usb_20_05122006.zip
and usb in a nutshell
http://www.beyondlogic.org/usbnutshell/usb1.htm
and LVR
**broken link removed**
and if you search on edaboard you can find these two books
USB Complete & USB Design By Example.

If you have questions you can send them to USB Forum
http://www.usb.org/developers/forum/

Salam
Hossam Alzomor
www.i-g.org