From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Thu, 22 Feb 2001 08:59:48 +0000 Subject: Re: Timing Facilities From: "Iain Sandoe" To: "Joseph P. Garcia" , Steve Poole Cc: linuxppc-dev@lists.linuxppc.org Mime-version: 1.0 Content-type: text/plain; charset="US-ASCII" Message-Id: <20010222085859.0271CDB9E0@atlas.valhalla.net> Sender: owner-linuxppc-dev@lists.linuxppc.org List-Id: Thu, Feb 22, 2001,Joseph P. Garcia wrote: > On Wed, 21 Feb 2001 23:24:57 -0600, Steve Poole 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/