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From: Paul Brook <paul@codesourcery.com>
Date: Sat, 11 Feb 2012 14:18:49 +0000
References: <cover.1328944806.git.peter.crosthwaite@petalogix.com>
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Subject: Re: [Qemu-devel] [PATCH v3 2/4] cadence_ttc: initial version of
	device model
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To: "Peter A. G. Crosthwaite" <peter.crosthwaite@petalogix.com>
Cc: peter.maydell@linaro.org, monstr@monstr.eu, edgar.iglesias@petalogix.com, qemu-devel@nongnu.org, John Linn <john.linn@xilinx.com>, duyl@xilinx.com, linnj@xilinx.com, afaerber@suse.de, john.williams@petalogix.com

> +static void cadence_timer_sync(CadenceTimerState *s)
> +{
>...
> +    r = (int64_t)cadence_timer_get_steps(s, s->cpu_time - old_time);
> +    x = (int64_t)s->reg_value + ((s->reg_count & COUNTER_CTRL_DEC) ? -r :
> r); +
> +    for (i = 0; i < 3; ++i) {
> +        if (is_between((int64_t)s->reg_match[i] << 16, s->reg_value, x)) {
> +            s->reg_intr |= (2 << i);
> +        }
> +    }

By my reading this will miss events if they happen after the timer wraps.
e.g. for a count-up timer with reg_match==1 and the tick callback happens to 
get delayed by 4 cycles, the timer may wrap straight to reg_value = 3.

Paul