As an Apple-invented technology, FireWire (IEEE 1394a and IEEE 1394b) should be (and usually is) one of the most solid and efficient means for interfacing with external peripherals. Indeed Apple's "i"-branded devices -- the iPod and iSight -- have, in large part, been made possible by the quick transfer rates, power sourcing, and hot pluggability offered by FireWire.
Occasionally, however, conflicts between FireWire-connected devices arise and can result in a variety of issues including DV cameras dropping frames, FireWire drives not mounting, and erratic behavior from the iPod (disappearing from iTunes, etc.). In the midst of these issues, you might also experience "buffer underrun" errors when trying to burn CDs or DVDs with FireWire-connected recorders.
The iSight is especially notorious for causing issues of this nature, and exhibiting symptoms.
There exist a number of methods for dealing with FireWire device interference, a few of which are explored here.
Switching Ports The first procedure you should try when experiencing a problem that you believe to be caused by device interference is to simply reconfigure the arrangement in which your FireWire peripherals are connected.
Try switching each device to a different port, or temporarily disconnecting one or more of the devices. In particular, if you are a PowerMac G5 owner, trying switching devices from the front to back ports or vice versa.
Adding an external hub In some cases, it appears that FireWire devices are not drawing enough power from the computer. This can cause a sundry of strange issues, including apparent conflicts between devices and unexpected power-offs during device operation. In these instances, adding an externally powered FireWire hub can clear things up.
One of the reasons an "under-powered" situation can occur is that different Mac models have varying power capacities available through their FireWire ports.
PowerBooks and iBooks have the least, generating around 7 watts. The iMac G5 also generates a relatively low amount of FireWire power, sharing 8 watts between its two FireWire 400 ports.
The Power Mac G5 shares 15 watts between its one FireWire 800 port and two FireWire 400 ports.
Place devices on different FireWire busses/Isolate the iSight Similar to the above procedure, adding another FireWire bridge -- via an extra PCI-based FireWire adapter or another means -- can eliminate conflicts from devices that reside on the same bridge.
Power cycling the system Simply cycling the power on your system may be enough to temporarily eliminate a few FireWire conflict issues.
Shut down your Mac, and disconnect all FireWire devices as well as the computer's power cord. Leave the system off for about 10 minutes, then plug it back in. First turn your Mac back on, then re-attach the FireWire devices one at a time and check for the conflict to resurface.
Disconnect specific FireWire devices (especially iSight) to check for conflicts As noted above, the most common cause of interference is Apple's own iSight. In case after case, simply disconnecting this single device has eliminated problems with other FireWire devices. Other devices often implicated in FireWire conflicts include video-related devices; cameras, the EyeTV, video decks, etc.
Disconnecting the iSight has proved particularly successful for an issue where the iPod disappears from the Desktop and from the iTunes playlist, while the iPod status screen cycles from the Apple logo to a "Do not Disconnect" message over and over.
The exact reasons why the iSight causes more than its fair share conflicts with other FireWire devices are many, and sometimes unclear. One potential source of conflict, however, could be the unit's high bandwidth usage.
The iSight captures video at a 640 x 480 pixel resolution, at 30 frames per second in millions of colors. Such throughput uses a significant chunk of the standard FireWire port's 400 Mbps bandwidth. As such, when other devices are connected, the bandwidth requirements for satisfactory performance may not be met.
Try disconnecting all FireWire devices, then adding them back one by one and repeating the originally failed operation to check for conflicts.
Apply the latest updates Make sure that your FireWire drives are using the latest firmware (check the manufacturers' Web site) and the most recent iPod update has also been applied.
Of higher importance, if you have an iSight, is the iSight 1.0.2 updater. In a large number of cases it has resolved conflicts caused by the camera.
Re-apply the most recent Mac OS X combo updater In some cases, re-applying the most recent combo updater can resurrect seemingly defunct FireWire ports and allow devices -- drives included -- to be recognized again.
The most recent combo updater is available from Apple's download page.
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