Re: usbnet ethernet duplex issue?

From: David Brownell
Date: Fri Jun 17 2005 - 14:46:42 EST

On Friday 17 June 2005 12:27 pm, Matt Mackall wrote:
> So the question is, what's up with duplex? Everything I can find about
> the hardware (including the ASIX datasheet) claims it's full-duplex
> capable but aside from the error counters, it's really behaving like a
> half-duplex device.

Well, USB itself is half duplex, but that wouldn't explain the issue
you're seeing. Maybe David Hollis or Phil Chang, who've both worked
with the ASIX parts, can cast some light on their quirks. This is
on a 2.6 kernel, I hope ... 2.4 kernels have packet queues a bit too
high up in the stack to get any real I/O overlap.

I know that when I've done "ttcp" Linux-to-Linux using a net2280 PCI
card [1] using CDC Ethernet protocols, I can get a bidirectional
transfer rate of around 25 Mbyte/sec (maybe a bit more, I forget;
that's untuned), so the bottleneck isn't the network or USB stacks.

- Dave

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