Firewire

Introduction

FireWire, originally developed by Apple Computer, Inc is a cross platform implementation of the high speed serial data bus –define by the IEEE 1394-1995 [FireWire 400], IEEE 1394a-2000 [FireWire 800] and IEEE 1394b standards-that move large amounts of data between computers and peripheral devices. Its features simplified cabling, hot swapping and transfer speeds of upto 800 megabits per second. FireWire is a high-speed serial input/output (I/O) technology for connecting peripheral devices to a computer or to each other. It is one of the fastest peripheral standards ever developed and now, at 800 megabits per second (Mbps), its even faster. 

Based on Apple-developed technology, FireWire was adopted in 1995 as an official industry standard (IEEE 1394) for cross-platform peripheral connectivity. By providing a high-bandwidth, easy-to-use I/O technology, FireWire inspired a new generation of consumer electronics devices from many companies, including Canon, Epson, HP, Iomega, JVC, LaCie, Maxtor, Mitsubishi, Matsushita (Panasonic), Pioneer, Samsung, Sony and Texas Instruments. Products such as DV camcorders, portable external disk drives and MP3 players like the Apple iPod would not be as popular as they are today with-out FireWire. 

Contents

1. Introduction

2. Topology

3. Transfers and transactions

4. Configurations

5. Normal arbitration

6. 1394a arbitration enhancements

7. Key features

8. Support for a wide range of devices

9. Hardware and software support

10. Conclusion

Transfers And Transactions 

Isochronous transfers: Isochronous transfers are always broadcast in a one-to-one or one-to-many fashion. No error correction or retransmission is available for isochronous transfers. Up to 80% of the available bus bandwidth can be used for isochronous transfers. The delegation of bandwidth is tracked by a node on the bus that occupies the role of isochronous resource manager. This may or may not be the root node or the bus manager. The maximum amount of bandwidth an isochronous device can obtain is only limited by the number of other isochronous devices that have already obtained bandwidth from the isochronous resource manager. 

Asynchronous transfers:  Asynchronous transfers are targeted to a specific node with an explicit address. They are not guaranteed a specific amount of bandwidth on the bus, but they are guaranteed a fair shot at gaining access to the bus when asynchronous transfers are permitted. Asynchronous transfers are acknowledged and responded to. This allows error-checking and retransmission mechanisms to take place. 

Normal Arbitration

Link Layer 

The link layer is the interface between the physical layer and the transaction layer. The link layer is responsible for checking received CRCs and calculating and appending the CRC to transmitted packets. In addition, because isochronous transfers do not use the transaction layer, the link layer is directly responsible for sending and receiving isochronous data. The link layer also examines the packet header information and determines the type of transaction that is in progress. This information is then passed up to the transaction layer. 

Transaction Layer 

The transaction layer is used for asynchronous transactions. The 1394 protocol uses a request-response mechanism, with confirmations typically generated within each phase. Several types of transactions are allowed. They are listed as follows: 

• Simple quadlet (four-byte) read

• Simple quadlet write

• Variable-length read

• Variable-length write

• Lock transactions 

Lock transactions allow for atomic swap and compare and swap operations to be performed. Transactions can be split, concatenated, or unified. Figure 3 illustrates a split transaction. The split transaction occurs when a device cannot respond fast enough to the transaction request. When a request is received, the node responds with an acknowledge packet. An acknowledge packet is sent after every asynchronous packet. 

Key Features

1)  Data transfer speeds up to 800 Mbps

2)  Distances up to 100 meters

3)  Plug-and-play connectivity

4)  Highly efficient architecture 

Plug-and-Play Connectivity

FireWire allows for true hot-swappable, plug-and-play connection of peripheral devices. There is no need to shut down the computer before adding or removing a FireWire device. Nor do you need to install drivers, assign unique ID numbers, or connect terminators. You can connect a few devices in a simple chain or add hubs to attach as many as 63 devices to a single FireWire bus. The number of available FireWire buses can be increased via PCI and CardBus cards. FireWire is a true peer-to-peer technology. Using a FireWire hub, multiple computers and FireWire peripherals can be connected at the same time. Such an arrangement would, for instance, enable two computers to share a single FireWire camera.

On-Bus Power

Like its predecessor, FireWire 800 provides significant amounts of power on its bus (up to 45 watts, with a maximum of 1.5 amps and 30 volts). This means that many devices can be powered through the FireWire cable and will not need their own power cables and adapters. For example, Apple’s iPod digital music player uses FireWire as its sole data and power connection. The player can recharge its built-in battery while it’s downloading new music from your computer. FireWire also includes an aggressive power management scheme; power is used only when actually needed.