linux-kernel - Re: mmap over HPET

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Message-ID: <75b66ecd0805281657k7b988bf1qa46e806810da0c17@mail.gmail.com>
Date:	Wed, 28 May 2008 19:57:11 -0400
From:	"Lee Revell" <rlrevell@...-job.com>
To:	Raz <raziebe@...il.com>
Cc:	"Linux Kernel" <linux-kernel@...r.kernel.org>
Subject: Re: mmap over HPET - 32 bit wrap arround

On Wed, May 28, 2008 at 6:19 PM, Raz <raziebe@...il.com> wrote:
> I am wondering wether someone can explain how hpet behaves. The bellow
> is a short program that reads from a mmaped /dev/hpet the time. I am
> running it and it looks that afer ~296 seconds the counter resets . I
> AM RUNNING  64bi KERNEL(2.6.18-8.el5)  and reading a 64BIT VARIABLE.
> my hpet is 14MHZ, so I  am guessing a 32bit wraparound ( ~296 * 14Mhz
> ) =  MAX_INT . but why ?
>

HPET counter can be either 32 or 64 bit.  Check COUNT_SIZE_CAP.

http://www.intel.com/hardwaredesign/hpetspec_1.pdf

Lee
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