matt@cs.city.ac.uk (Matthew Sillitoe) (08/22/90)
Problem: Need to syncronise two clocks one at 25MHz, and one at 20MHz, under
the control of one TTL input. The clock needs to switched from one
to the other without producing 'glithches'. The 20MHz, and 25MHz
clocks are pregenerated.
Please mail any sugesstions and/or references etc etc to the above address.
Thanks in Advance.
Matt.mark@mips.COM (Mark G. Johnson) (08/23/90)
In article <1990Aug22.164935.12358@cs.city.ac.uk> matt@cs.city.ac.uk (Matthew Sillitoe) writes: >Problem: Need to syncronise two clocks one at 25MHz, and one at 20MHz, under > the control of one TTL input. The clock needs to switched from one > to the other without producing 'glithches'. The 20MHz, and 25MHz > clocks are pregenerated. William K. Stewart, "A Solution to a Special Case of the Synchronization Problem", IEEE Trans. Computers, 1985-6 (don't have page #'s or exact date on my preprint). From the Abstract: "... This paper describes a synchronizer that exhibits an arbitrarily low failure rate and a short propagation delay for the special case of synchronizing a signal that is synchronous with some periodic signal." Note the phrase "special case" in the title -- that's the key. The authors haven't cheated Mother Nature, they've just found an interesting and useful subproblem (data input to be synched is *periodic*) which is tractable. Potential flamers, read the paper... In the paper they design *and build* *and measure* physical TTL hardware that accepts data in from an 8MHz periodic source, and synchronizes it with a local 10MHz clock. Average latency is 60ns, i.e. less than one tick of the local clock. -- -- Mark Johnson MIPS Computer Systems, 930 E. Arques M/S 2-02, Sunnyvale, CA 94086 (408) 524-8308 mark@mips.com {or ...!decwrl!mips!mark}
davidb@brac.inmos.co.uk (David Boreham) (08/30/90)
In article <41045@mips.mips.COM> mark@mips.COM (Mark G. Johnson) writes: >William K. Stewart, "A Solution to a Special Case of the Synchronization >Problem", IEEE Trans. Computers, 1985-6 (don't have page #'s or exact date >on my preprint). From the Abstract: "... This paper describes a synchronizer >that exhibits an arbitrarily low failure rate and a short propagation delay >for the special case of synchronizing a signal that is synchronous with >some periodic signal." > OK, I give up. Just spent a hour reading 13 years of IEEE Trans on Computers and can't find this paper. There were a couple of copies missing though. I do remember seeing the thing a few years ago so could someone please post the exact reference. Thanks. David Boreham, INMOS Limited | mail(uk): davidb@inmos.co.uk or ukc!inmos!davidb Bristol, England | (us): uunet!inmos.com!davidb +44 454 616616 ex 547 | Internet: davidb@inmos.com