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Re: [Qemu-devel] [PULL 17/28] hw/ptimer: Perform counter wrap around if

From: Peter Maydell
Subject: Re: [Qemu-devel] [PULL 17/28] hw/ptimer: Perform counter wrap around if timer already expired
Date: Fri, 24 Jun 2016 17:02:38 +0100

On 24 June 2016 at 16:58, Mark Cave-Ayland
<address@hidden> wrote:
> On 06/06/16 15:47, Peter Maydell wrote:
>> From: Dmitry Osipenko <address@hidden>
>> ptimer_get_count() might be called while QEMU timer already been expired.
>> In that case ptimer would return counter = 0, which might be undesirable
>> in case of polled timer. Do counter wrap around for periodic timer to keep
>> it distributed. In order to achieve more accurate emulation behaviour of
>> certain hardware, don't perform wrap around when in icount mode and return
>> counter = 0 in that case (that doesn't affect polled counter
>> distribution).

> Whilst testing Artyom's qemu-system-sparc patch today, I noticed another
> regression which I've bisected down to the above commit.
> Booting my NetBSD/OpenBSD test images with current git master causes the
> following warning to appear on the console: "WARNING: negative runtime;
> monotonic clock has gone backwards".
> Could this be a regression or does qemu-system-sparc make an incorrect
> assumption as to how the timer should work in this scenario?

I'm not sure -- Dmitry ?

-- PMM

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