MS Patch available for FireWire 800 and SP2

On December 17, 2004, Microsoft published a Knowledge Base article about the FW800 slowdown problem under SP2, confirming the behavior to be a problem of SP2. At the same time MS released a file update, which has to be installed manually. The article says this update will not be included in later updates and hotfixes, so it must be installed manually whenever needed. The link to the article:

http://support.microsoft.com/kb/885222/en-us

Quote: After you install Windows XP Service Pack 2, some 1394 devices (such as digital cameras that use S400 speed) may not perform as expected. Install this update to help prevent this issue.

So does it fix the Firewire 800 problems?

Yes, it does. Almost...

The patch installs a new ohci1394.sys, and adds an entry SidSpeed to the OHCI controller in the registry. The documentation from Microsoft on this patch is disappointing. Here's what we found out:

• After installing this patch, no-name FireWire devices which operate in asynchronous mode seem to be able to use S800, without any further firmware updates etc. The IBM disk in the noname drive enclosure that we use (SpeedStar) now reaches 51 MByte/s (38 at S400, 10 at S100). So this patch seems to give full speed here. Note that the setting SidSpeed had no (in words: none) effect on the transfer rate. It stayed at 51 MB all the time.
   
• After installing this patch, FireWire devices which operate in isochronous mode and support higher speeds are no longer slowed down to S100, but to S400. This of course helps any Firewire 800 device, but it still needs our own patch to reach S800 (in one direction). Note that the SidSpeed setting controls the transfer rate. Isochronous devices will slow down to S100, S200 or S400 when changing the reg entry to 0, 1 or 2. According to MS a setting of 3 is expected to give the old behavior of SP1 - which is not true. While SP1 enabled S800, SP2 with this patch enables only S400.

What does this all mean?

DAWSTORE recommends to install this patch. It will help you to stay compatible, and also delivers nearly the highest speed possible when using FireWire 800 devices. Only users working with three FireWire devices could gain a bit more performance by using the old SP1, but might run into trouble at other places. Usually the combination of driver/firmware together with SP2 and this MS patch gives trouble-free operation of up to three FireWire 800 devices, and with most other FW devices out there.

Last update: 01/31/2005