Apple has released Power Mac G5 Uniprocessor Firmware Update 5.1.5f2. Apple explained the release, “after applying the Power Mac G5 Uniprocessor Firmware Update 5.1.5f1 to some 1.6 GHz computers, unexpected issues might occur. But you can install Firmware Update 5.1.5f2 to fix them. What unexpected issues? It could be a kernel panic, the loss of USB function with some keyboards or mouse tracking devices, Bluetooth USB modules that don’t respond five minutes after starting up, or interrupted audio playback in iTunes. Disconnecting and reconnecting devices does not help. Removing some or all non-Apple memory (RAM) usually stops the issue.”
More info and download link here.