From: David Ferguson <email@hidden>
To: b johnny <email@hidden>
CC: email@hidden
Subject: Re: slow transfer rate
Date: Sun, 16 Jan 2005 17:56:41 -0800
Its sounds like your high-speed devices (maxPacketSize == 512
bytes) is plugged into a full-speed hub (where the spec limits it
to maxPacketSize == 64 bytes).
Perhaps you should try plugging your device directly into a
computer with high-speed support.
thks barry,
but i still dun quite understand what u mean. i am using a G5 Mac
and i am pretty sure it has a high speed hub in it. i have already
try plugging it into all the USB ports but to no avail. do i nd to
make changes in my code to ensure that it transfers at 512 Bytes? is
this possible?
Perhaps this will help you understand.
You will need to do some investigation yourself. Determine:
- Is your device enumerating at high-speed? You can use System
Profiler to look under the USB list to see if your device shows up
under a full-speed controller or a high-speed controller.
Alternately, you could use a USB bus analyzer to examine the
enumeration and see what happens.
- Use the utility USB Prober to examine the descriptor for your
device. What is the maxPacketSize of the endpoint you are reading
from?
- Even if your device has a maxPacketSize of 512, we've seen some
devices with bad firmware that only respond with 64 bytes of data.
You will need the USB bus analyzer to see this behavior. Can you
talk to folks responsible for the firmware in your device to see if
they can fix this?
- Assuming your device is actually running at hi-speed, and still
returning short 64 byte packets, you could re-code your driver to
expect this. Issue multiple reads of 512 bytes, but deal with the
fact that they only return 64 bytes. You will need to use asynch
requests so that you can have multiple transactions outstanding at
one time. You probably need as many requests as the number of 64
byte packets your device can supply in 1ms.
Good Luck,
David Ferguson
USB Software Team
Apple Computer
_______________________________________________
Do not post admin requests to the list. They will be ignored.
Usb mailing list (email@hidden)
Help/Unsubscribe/Update your Subscription:
http://lists.apple.com/mailman/options/usb/email@hidden
