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Re: [Discuss-gnuradio] New implementation for fusb_linux withoutallocs/f

From: Eric Blossom
Subject: Re: [Discuss-gnuradio] New implementation for fusb_linux withoutallocs/frees
Date: Tue, 24 Feb 2009 11:37:42 -0800
User-agent: Mutt/1.5.18 (2008-05-17)

On Tue, Feb 24, 2009 at 01:07:34PM -0500, Marcus D. Leech wrote:
> Eric Blossom wrote:
> > Marcus, in my experience, USB performance has not be limited by cpu
> > cycles.  It seems to be primarily a function of the design of the host
> > controller, the firmware in the device, and a reasonable way to get
> > the data into user mode.  In most apps I've benchmarked, the overhead
> > of all usrp related stuff is typically on the order of 5 to 10% of the
> > total cycles consumed.
> >
> > Eric
> >
> >   
> OK, so improving total USB cycle counts in user mode from 10% to 5%
> perhaps wouldn't noticeably improve
>   things like overruns--is that what you're saying?

Overruns are generally caused because your signal processing can't
keep up, not that there's a problem with handling the USB.

> So, in your experience what is the sh*t-hottest USB controller out
> there, and is it available on a PCI or PCI-E card?

Once the controller can handle 32MB/s, you're golden.  Pretty much any
of the onboard controllers over the last few years work fine.

Measure twice, cut once.  Time be time.  


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