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Re: [Qemu-devel] [PATCH] USB 2.0 EHCI emulation

From: Dor Laor
Subject: Re: [Qemu-devel] [PATCH] USB 2.0 EHCI emulation
Date: Tue, 08 Jan 2008 10:43:09 +0200

On Tue, 2008-01-08 at 01:30 +0000, Paul Brook wrote:
> > -The host kernel was configured with dynamic tick & hi-res timers, to
> > allow the desired timer resolution. USB 2.0 microframe is 125usec.

It still works even without accurate timing demands.
Only isochronous mode will have problems and it is not yet supported for

> Requiring a 8kHz timer is a non-starter.
> The 100kHz "retry" timer is even more bogus. 
> Qemu isn't capable of this kind of realtime response. You need to figure out 
> an implementation that doesn't require extremely fine grained timers. In 
> paractice you're unlikely to get better than 10ms timer resolution, and 100ms 
> latency isn't that uncommon.
> Paul

Latest Linux host compiled HR_TIMER and DYN_TICK can give pretty good
accuracy, surely it can provide 1khz and probably even 8khz


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