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Advantages of FireWire on PCIe

Posted: 12 Sep 2011     Print Version  Bookmark and Share

Keywords:PCI Express  FireWire  networking 

In addition to the above protocol enhancements PCI Express, as a serial protocol, offers significant system board design simplification and resultant reduced cost. PCI Express eliminates the burden of supporting 32bit or 64bit wide address and data buses required for PCI. System boards that are solely PCI Express based can now be reduced to 4 layers only and placement and routing of the board becomes much easier, which makes routing high speed 1394 differential pair signals easier.

PCI Express-based 1394 host controllers can now be supported in much smaller packages and allow placing multiple controllers on a single PCI express system board (figure). The 10x reduction in trace routing enabled by PCI Express also allows more freedom in the placement of the 1394 connector resulting from easier routing the PCI Express and1394 signals.

PCI Express enhances power savings compared to PCI by allowing not only software controlled power states, but activity based Active State Power Management (ASPM) which saves power at run time without software intervention. PCI Express gen2 allows for level margining, which optimises power based on channel quality, and gen3 introduced dynamic equalisation, which optimises signal integrity and power efficiency at the same time.

For mobile platforms PCI Express offers an integrated hot swap solution that eliminated the need for a dedicated controller such as the card bus controller needed for a PCI based mobile architecture. Operating System support for multiple 1394 host controllers is provided through the IEEE 64bit serial number supported by PCI Express that uniquely identifies each controller and is currently required by the Vista operating system.

Utilising PCI Express based 1394 host controllers brings Reliability, Availability and Serviceability (RAS) features to 1394 system design. PCI Express requires standard on-chip hardware for error detection, correction and reporting that is not required in PCI.

Robust multi-level error reporting and correction architecture allows correctable errors to be handled on the fly without system software intervention, non-fatal errors to be corrected by software and only fatal errors cause interruption of normal operation in extreme cases.

Error reporting is standardised by the specification and eliminates the need for an extra software driver to handle vendor proprietary error mask bits, which minimises software support for 1394 products. By comparison, PCI based host controllers could only detect simple parity errors.



Figure: PCIe enables significant efficiencies in board utilisation (below), compared with PCI (above).

In addition to all the features and benefits detailed above, PCI Express includes features that have yet to become productized benefits for the consumer. These features include: support for virtualisation; latency tolerance reporting (LTR); optimised buffer fill/flush (OBFF); support for 64bit 1394 open host controllers (OHCI) and simplified support for multiple 1394 host controller system solutions. Simply stated, PCI Express based host controllers are "future proofed."

About the author
David Thompson is a Distinguished Engineer in the Systems Applications Engineering area at LSI Corp. He has an MSEE from Stanford University, is a Senior member of IEEE and has been with Bell Laboratories and its inheritors for 31 years before becoming LSI Corporation. His group is currently developing 1394, USB and other serial-bus technology standard products for LSI. He is also serving his tenth year as a member of the 1394 Trade Association's Board of Directors and is Chair of the 1394 TA Qualification Review Board.

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