From: "Iain Sandoe" <iain@sandoe.co.uk>
To: "Joseph P. Garcia" <jpgarcia@execpc.com>, Steve Poole <sp@is2-isnot.com>
Cc: linuxppc-dev@lists.linuxppc.org
Subject: Re: Timing Facilities
Date: Thu, 22 Feb 2001 08:59:48 +0000 [thread overview]
Message-ID: <20010222085859.0271CDB9E0@atlas.valhalla.net> (raw)
Thu, Feb 22, 2001,Joseph P. Garcia wrote:
> On Wed, 21 Feb 2001 23:24:57 -0600, Steve Poole <sp@is2-isnot.com> wrote:
>> I have written a small assembly fragment to read the TB register that runs
>> under Linux (YDL/BLL). What is the definition of a "tick" or "jiffie" under
>> Linux. When some code is run under MacOS (400MHz G4) the results are
>> *faster* (the numbers returned are lower) than when I run on a 500MHz G4. I
>> appreciate any input.
>
> I beleive there are 1*HZ jiffies in one second. Used in the kernel's
> timer_list struct (to name one use), which basically has the kernel run a
> function at a specific time. ex, setting the 'expires' value to (jiffies +
> HZ) will cause it to run one second from now.
the VEA TB rate is not fixed to the processor clock - but is related to the
bus freq (IIRC). You can find the TB rate from OF (but beware of a report
that says the values stored are not always correct).
I did a similar thing a while ago - and, because high precision was not
required, just used gettime() and a few seconds sleep... to calibrate.
ciao,
Iain.
** Sent via the linuxppc-dev mail list. See http://lists.linuxppc.org/
next reply other threads:[~2001-02-22 8:59 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2001-02-22 8:59 Iain Sandoe [this message]
-- strict thread matches above, loose matches on Subject: below --
2001-02-22 5:24 Timing Facilities Steve Poole
2001-02-22 6:10 ` Joseph P. Garcia
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