Re: VME320? (fwd)

[Elton Smith <elton@jlab.org>]

Hi Fernando,

We can discuss this at next meeting. Also, any comments can be sent
directly to the halld-jlab list.

Elton.




On Wed, 5 Sep 2001, Fernando J. Barbosa wrote:

> Hi, Elton, Chris. The advantage of adopting VME320 over VME64x is that one
> can still use VME64x compliant controllers with a VME320 backplane. However,
> the reverse is not true because a VME64x backplane cannot handle 320
> Mbytes/sec data transfers as it was not designed for such. In view of future
> upgrades, VME320 is much more attractive. My point is, why commit to an
> "obsolete" standard (VME64x) that some of us judge already marginal in terms
> of data transfer speeds?
>     Best regards,
>         Fernando
>
> ----- Original Message -----
> From: "Elton Smith" <elton@jlab.org>
> To: <halld-jlab@jlab.org>
> Sent: Wednesday, September 05, 2001 2:33 PM
> Subject: Re: VME320? (fwd)
>
>
> >
> >
> > ---------- Forwarded message ----------
> > Date: Wed, 05 Sep 2001 09:56:28 -0700
> > From: Chris Cuevas <cuevas@jlab.org>
> > To: Elton Smith <elton@jlab.org>
> > Subject: Re: VME320? (fwd)
> >
> > Elton,
> >
> > I have attached a brief paper on the subject of VME protocols and newer
> > developments/modifications to the original 1981 VME standard.  Fernando
> points
> > out some positive reasons to consider the VME320 spec and if memory serves
> > this has been discussed before.  I believe one of the primary concerns
> with
> > using the '320 spec was the issue of proprietary controllers[cpu].  At any
> > rate, this topic will impact the "final" design for the Hall D TDC.
> >
> > -Chris
> > x5053
> > ~~~~~~~~~~~~~~~~~~
> >
> > Elton Smith wrote:
> >
> > > ---------- Forwarded message ----------
> > > Date: Tue, 4 Sep 2001 14:50:01 -0400
> > > From: Fernando J. Barbosa <barbosa@jlab.org>
> > > To: Elton Smith <elton@jlab.org>
> > > Subject: VME320?
> > >
> > > Hi , Elton. At our last meeting, we briefly discussed the possibility of
> > > using dedicated pins for distribution of the reference clock, trigger,
> > > syncreset and start signals in differential mode. The TDCs will also
> have
> > > these input pins present on the front panel for use in systems where the
> > > backplane implementation is not required nor feasible.
> > >
> > >     Standard VME backplanes have 64 pins of User Defined pins on P2/J2.
> > > Some of these could be used for signal distribution by means of wired
> > > piggy-back connectors, as opposed to designing a special backplane.
> > >
> > >     VME64x adds 46 User Defined pins to P2/J2 and has standard
> provisions
> > > for an additional connector (P0/J0) between the P1/J1 and P2/J2
> > > connectors. This connector adds 95 User Defined pins. Boards using the
> > > P0/J0 connectors cannot be installed on standard VME backplanes as there
> > > is a bar for support and rigidity of the backplane in this location. The
> > > piggy-back connections mentioned above can also be implemented on this
> > > backplane.
> > >
> > >     The most recent VME standard is called VME320 for 320 Mbytes/sec
> > > transfers. VME320 builds on VME64x with two distinct enhancements:
> > > Synchronous Source Termination (SST) and "lumped" backplane layout. Two
> > > edge transfers are also implemented as on VME64x. The traces in VME320
> > > (a.k.a. 2eSST VME) are routed from slot 1 (master) to slot 11 and then
> > > from slot 11 to all other slots (2 through 21). This technique doubles
> the
> > > speed on the backplane as compared to earlier VME standards as those
> > > backplanes had traces routed from slot 1 to slot 2, from slot 2 to slot
> 3
> > > and so on. Because of the reflective nature of those earlier backplanes,
> a
> > > signal from slot 1 to slot 2 could only be qualified after the signal
> > > propagated to slot 21 and back to slot 2. The SST doubles the speed once
> > > more to 320 Mbytes/Sec because transmission is synchronous and does not
> > > require the handshake overhead required for master/slave
> acknowledgements.
> > > VME320 backplanes are already available.
> > >
> > >     I suggest adopting VME320 as a standard for Hall D, as well as, a
> > > standard for future upgrades at the lab. We should also discuss signal
> > > distribution schemes for backplanes and systems in general at our next
> > > Hall D TDC meeting.
> > >
> > >     Best regards,
> > >         Fernando
> >
>
>

-- 
Elton Smith
Jefferson Lab
elton@jlab.org
(757) 269-7625