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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
ehci.
> 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
Dor