USB for Embedded Device ASHWINI MISHRA

Transcription

1 USB for Embedded Device ASHWINI MISHRA

2 Outline Introduction Why USB History of USB Architecture USB on Embedded systems Future References

3 Introduction USB( Universal Serial Bus) is a specification to establish communication between devices and a host controller (usually personal computers), developed by Intel Compaq and Microsoft joined latter by Lucent and Philips

4 The History of USB USB 1.0: January Specified data rates of 1.5 Mbit/s and 12 Mbit/s. Had many limitations, wasn t widely adopted USB 1.1: September Fixed bugs of earlier version, was widely accepted. USB 2.0: April Added Speed of 480 Mbit/s USB On-the-Go: December Host not needed any more. Micro USB: April 2007.Specially for Mobile Phones USB 3.0: (5 Gbit/s) In pipeline. Expected to be commercially available in 2010.

5 Why USB? Laborious and error-prone configuration of the RS- 232 port Incompatible RS-232 connectors Point to point nature of connections if we share multiple devices means a lot of cable and connectors are required High power required for transceivers

6 Archicture Based on Tiered star Topology Maximum number of Tiered connected to 6 It can connected maximum of 127 devices Length of cable limited to 5m

7 Connectors Type- A Type-B mini-b-type mini-a-type micro-ab-type

8 Host Concept Host is master Devices communicated to Host Device cant communicate directly HOST Device1 Device2

9 Classification Of USB On Basis of Host UHCI (Universal Host Controller Interface) developed by Intel which puts more of the burden on software (Microsoft) and allowing for cheaper hardware OHCI (Open Host Controller Interface) developed by Compaq, Microsoft and National Semiconductor which places more of the burden on hardware (Intel) and makes for simpler software. For the high-speed data rate of USB Version 2.0, all of the participants agreed to the EHCI (Enhanced Host Controller Interface) specification.

10 USB on the Go Devices can become limited role hosts Marked the emergence of usage of USB in portable platforms Removed the often-cited limitation that USB requires a desktop computer or equivalent to act as a host. Device 1 Device 2

11 Micro USB Universal Charger Solution as its "energy-efficient one-charger-fits-all new mobile phone solution", and added: "Based on the Micro-USB interface, UCS chargers will also include a 4-star or higher efficiency rating - up to three times more energy-efficient than an unrated charger.

12 Challenges of implementing USB on an embedded platform USB on a PC MB and GB of memory available USB on an embedded device Only KB of memory available 2 GHz micro-processor Hard drive space in GB greater than 100 GB now a days No hard drive at all Many skill engineers are well versed in designing PC based USB applications MHz Processor No hard drive at all USB on embedded systems is relatively new and not many people have idea

13 USB on Embedded Systems Any embedded device with a processor has a potential to act as a USB host. Potential Embedded platforms: Cell Phones PDAs Digital Cameras Set top Boxes and more.

14 USB Devices Based on Linux Write custom Linux kernel module. Provides the power to do sophisticated things like emulating a file system etc. Use USB bus as a high speed serial port. Implemented in the Linux kernel for Strong ARM processors. Straightforward approach and mostly used. Ethernet over USB. Linux has modules to implement both the host and device sides of this capability. The Linux kernel for the ipaq uses this, since the ipaq (pocket PC) hardware has neither an accessible serial port nor a dedicated network interface.

15 Why Linux for using USB? Linux not only contains drivers for host controllers, but for device controllers as well. These controller drivers enable Linuxto communicate with a host computer (which may or may not be running Linux as well). USB communications under Linux are flexible and easy to use.

16 USB3 Features In a nutshell, USB 3.0 promises the following: Higher transfer rates (up to 4.8 Gbps) Increased maximum bus power and increased device current draw to better accommodate power-hungry devices New power management features Full-duplex data transfers and support for new transfer types New connectors and cables for higher speed data transfer...although they are backwards compatible with USB 2.0 devices and computers (more on this later)

17 Why USB3 achieve extra performance? USB 3.0 achieves the much higher performance by way of a number of technical changes. Perhaps the most obvious change is an additional physical bus that is added in parallel with the existing USB 2.0 bus. This means that where USB 2.0 previously had 4 wires (power, ground, and a pair for differential data), USB 3.0 adds 4 more for two pairs of differential signals (receive and transmit) for a combined total of 8 connections in the connectors and cabling.

18 What new applications does USB 3.0 enable? Digital video cameras and digital still cameras with USB interface Multi-channel audio interfaces External hard drives - capable of more than twice the throughput available from USB 2.0, not to mention bus-powered portable drives that require non-compliant Y-cables to get the current they require for reliable operation External media such as Blu-Ray drives

19 References Jan Axelson, USB Complete Everything You Need to Develop Custom USB Peripherals, 3rd edition