The G5 seems to be able to handle one less packet per microframe in
BULK mode than the powerbooks or the mac mini. I'm not sure if this is
because of how the HC is interfaced to the rest of the machine, or just
because there is more stuff already on the USB bus internally (HUBs,
etc).
I guess it is quite frustrating to take the time to design a USB device
that complies with the USB 2.0 performance specs, then to find that one
has to do extensive detective work to find out what the specs are on
the host controllers particularly, and the device only runs at 50% of
the spec on a great day. I understand that this is not fault of the
computer manufacturer. However, If nobody lists how many packets the HC
can handle per microframe, and what the REAL specs are(not the 480Mbps
singaling rate yadda yadda), how are we supposed to design high
performance USB devices? It's like shooting in the dark. :P
Next time, firewire. :D
Lesson learned.
Cheers,
Juan
On Jun 14, 2005, at 12:16 AM, Fernando Urbina wrote:
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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