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Re: slow transfers to a full-speed device

Subject: Re: slow transfers to a full-speed device
From: David Ferguson <email@hidden>
Date: Tue, 14 Jun 2005 23:03:59 -0700
Delivered-to: email@hidden
Delivered-to: email@hidden

This is a really inefficient way to send bytes to a device. Try using a much larger buffer to reduce the overhead per transfer. I would think you'll see a significant improvement if you use even 32k, but you should try transfers from 4k (the pagesize of MacOS X) to 128k. You may also want to make sure your data is aligned on a 64-byte boundary to put the maximum number of bytes per transfer descriptor (a USB controller data structure used inside the IOUSBFamily).

David Ferguson
Apple Computer

At 8:52 PM -0700 6/14/05, Eric Smith wrote:

I've got a full speed USB device, and am writing data in 64 byte packets to a bulk endpoint. This is just sitting in a for loop, doing a bunch of WritePipe() calls. My download speed over several megabits is only about 500Kbps. I'm using Tiger, and a dual 1.8 G5. I get about the same performance on a G4 iBook running Tiger. The same USB device gets about 6Mbps download on a windows-based machine. I did not write the windows code, so I don't know any of the details of that implementation.
Any ideas or suggestions?
Thanks,
Eric Smith
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References:
	>slow transfers to a full-speed device (From: Eric Smith <email@hidden>)

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