FW: Period Tolerance history (fwd)

[Jim McGrath]

* From the T10 (formerly SCSI) Reflector (t10 at symbios.com), posted by:
* Jim McGrath <Jim.McGrath at quantum.com>
*

In that case I assume that the tolerance would roughly scale with speed, and
so a reduction in the tolerance value is in order.  Any inputs (from people
familiar with the PLL tolerances and the like) on what it should be?

Jim


> -----Original Message-----
> From:	John Lohmeyer [SMTP:lohmeyer at ix.netcom.com]
> Sent:	Wednesday, September 09, 1998 11:31 AM
> To:	T10 Reflector
> Subject:	Fwd: FW: Period Tolerance history (fwd)
> 
> * From the T10 (formerly SCSI) Reflector (t10 at symbios.com), posted by:
> * John Lohmeyer <lohmeyer at ix.netcom.com>
> *
> Rob Elliott has had trouble posting the following message to the T10
> Reflector.  I am trying to forward it on his behalf.  -- John
> 
> >Forwarded message:
> >>From relliott Wed Sep  9 09:11:35 1998
> >Subject: Period Tolerance history
> >To: t10 at symbios.com
> >Date: Wed, 9 Sep 1998 09:11:35 -0500 (CDT)
> >X-Mailer: ELM [version 2.4 PL24beta]
> >Content-Type: text
> >Content-Length: 1133      
> >
> >I looked through the archives and found two proposals related to the 
> >mysterious "period tolerance."  These should help explain the history 
> >of those numbers.  
> >
> >94-142r1 (July 1994), by Bill Galloway at Compaq, introduced the concept.
> 
> >He asked for 0.25% transmit period tolerance and 0.5% receive period 
> >tolerance.  That corresponds to these values (although only Fast-10 
> >existed then):
> >            Period  Receive Tolerance   Transmit Tolerance
> >Fast-10     100 ns      0.5 ns          0.25 ns
> >Fast-20     50 ns       0.25 ns         0.125 ns
> >Fast-40     25 ns       0.125 ns        0.063 ns
> >
> >97-268r1 (November 1998) by Tak Asami at Adaptec, complained that these 
> >were too tight for PLL-based designs running at Fast-40.  He proposed 
> >changing the transmit period tolerance to 1.0 ns and the receive period 
> >tolerance to 1.1 ns.
> >
> >Apparently both proposals were accepted. 
> >
> >See:
> >http://www.symbios.com/t10/io/t10/document.94/94-142r1.pdf
> >http://www.symbios.com/t10/io/t10/document.97/97-268r1.pdf
> >
> >
> >-- 
> >Rob Elliott      UNIX mailto:relliott at hobbit.eng.hou.compaq.com    
> >Houston, TX        PC mailto:Robert.Elliott at compaq.com
> > 
> *
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