The architecture in the PowerMac G5's is different than in the other
machines, so it is entirely possible that the performance is
different. The USB controller needs to go out to main memory to
traverse the data structures in order to find out what works needs to
be done. This takes time and you'll see it in a bus trace as the
inter-packet gap.
I can say that I am not surprised by your findings, but you should
make sure and understand why (i.e. look at the interpacket gap in
both configurations). Other issues like the controller's efficiency
are not pertinent as all the machines we ship use an NEC controller.
--
Fernando Urbina
USB Technology Team
Apple Computer, Inc.
On Jun 8, 2005, at 4:53 PM, Juan Pertierra wrote:
I have a High Speed USB device/software combo that runs fine on the
Mac Mini and Apple powebooks. It does use a considerable amount of
bandwidth in real-time, right now it is about 22MB/sec.
I have recently tested this on the brand new Apple Dual 2.7Ghz G5
with 2.5GBytes of RAM, and it cannot keep up, i loose data. I even
installed a PCI card with a NEC HC controller, and disconnected all
other USB devices, i still lost data.
Is there something I can do to solve this problem or is the G5
architecture such that it can't even handle 22MB/sec over High
Speed USB? I have tested the whole system extensively and it runs
perfectly on even the slowest mac mini.
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