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

[Dor Laor]

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