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From: henry@utzoo.UUCP (Henry Spencer)
Newsgroups: net.arch,net.micro.68k
Subject: Re: Asynchronous State machines
Message-ID: <6144@utzoo.UUCP>
Date: Sat, 16-Nov-85 22:07:10 EST
Article-I.D.: utzoo.6144
Posted: Sat Nov 16 22:07:10 1985
Date-Received: Sat, 16-Nov-85 22:07:10 EST
References: <389@aum.UUCP> <6077@utzoo.UUCP> <395@aum.UUCP> <6111@utzoo.UUCP>
Organization: U of Toronto Zoology
Lines: 21

> Say, Henry, perhaps you should explain what you mean when you say
> you've done the math and synchronous state machines can be run faster
> than 50 nS?

I mean, specifically, that I have done the metastability calculations.
Yes, I know about the issue.  My calculations were based on the formulae
that accompanied the table in IEEE Transaction on Computers (I think it
was) a while ago, and the data in the table, and a hefty safety margin.

> For something reasonable like once every 40 years at say a 1 MHz rate,
> I recall a device like a S FF would take 70-80 nS. I understand the
> new F logic settles faster and that may be the origin of the 50 nS
> number quoted.

I don't remember the time needed for STTL, since in my opinion nobody in
his right mind uses STTL now that FTTL is available.  FTTL does indeed
settle faster.  Note the relationship between settling time and synchronizer
performance is *not* linear.  FTTL is not just better, it is lots better.
-- 
				Henry Spencer @ U of Toronto Zoology
				{allegra,ihnp4,linus,decvax}!utzoo!henry