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

From: Arnon Gilboa
Subject: RE: [Qemu-devel] [PATCH] USB 2.0 EHCI emulation
Date: Tue, 8 Jan 2008 00:31:30 -0800

The WinXP guest seems to work fine with the timer resolution, accuracy
and latency of qemu. The problem with linux guests might be related to
this issue.
I will test the ehci emulation without the specified kernel config and
see how can we handle timing issues in a more qemu-oriented way. Any


-----Original Message-----
From: Paul Brook [mailto:address@hidden 
Sent: Tuesday, January 08, 2008 3:30 AM
To: address@hidden
Cc: Arnon Gilboa; KVM; Roni Luxenberg
Subject: Re: [Qemu-devel] [PATCH] USB 2.0 EHCI emulation

> -The host kernel was configured with dynamic tick & hi-res timers, to 
> allow the desired timer resolution. USB 2.0 microframe is 125usec.

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.


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