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From: Paul Brook <paul@codesourcery.com>
Subject: Re: [Qemu-devel] Re: Precise guest instruction count.
Date: Wed, 11 Mar 2009 13:13:20 +0000
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To: qemu-devel@nongnu.org
Cc: Steffen Liebergeld <usenet@gmx.eu>

> By turning of all timers in Qemu I hope to disable all timer interrupts for
> the guest. The results I get are not correct for the first time the code is
> run, but for all subsequent runs. In the first run, the instruction count
> has 12 additional instructions, which are not actually executed.
>
> What is the cause of those additional instructions?

Probably you're not reading the correct value. Like I said, for performance 
reasons the counter is only valid at certain points.

Try instead implementing your timer as a peripheral.

Paul