Re: mmap over HPET - 32 bit wrap arround

From: Lee Revell
Date: Wed May 28 2008 - 19:57:39 EST


On Wed, May 28, 2008 at 6:19 PM, Raz <raziebe@xxxxxxxxx> 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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