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Re: [Qemu-devel] implementing architectural timers using QEMU timers

From: Max Filippov
Subject: Re: [Qemu-devel] implementing architectural timers using QEMU timers
Date: Tue, 10 Jan 2017 10:45:06 -0800

On Tue, Jan 10, 2017 at 1:10 AM, Frederic Konrad
<address@hidden> wrote:
> On 01/09/2017 04:18 PM, Max Filippov wrote:
>> I'm trying to reimplement xtensa CCOUNT (cycle counter) and
>> CCOMPARE (CCOUNT-based timer interrupts) using QEMU
>> timers. That is CCOUNT value is derived from the
>> QEMU_CLOCK_VIRTUAL clock and CCOMPARE interrupts are
>> generated from the QEMU_CLOCK_VIRTUAL timer callbacks.
>> The code is here:
>>   https://github.com/OSLL/qemu-xtensa/commits/xtensa-ccount
>> I've got the following issues doing that:
>> - I thought that could be improved in -icount mode, so I tried that.
>>   It is better with -icount, but it's still not 100% accurate. That is
>>   I was able to observe guest reading QEMU clock value that is
>>   past QEMU timer deadline before that timer callback was
>>   invoked.
>>   That sounds like a bug to me, is it?
> Did you try "sleep" icount option?
> eg:
> -icount 1,sleep=off

That doesn't seem to change anything.

-- Max

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