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From: homeis@cs3
Newsgroups: comp.sys.transputer
Subject: Re: C004 crossbar communication delays
Message-ID: <7165@ifi.informatik.uni-stuttgart.de>
Date: 24 Jan 91 15:29:19 GMT
Sender: news@ifistg.uucp
Organization: IPVR, Univ. Stuttgart, W-Germany
Lines: 28
Originator: homeis@cs3

Norman Goldstein (goldsten@cs.ubc.ca) writes:

>On page 55 of "Transputer Technical Notes", INMOS Limited, 1989, it is
>stated that using a crossbar connection "... introduces a 1.6 to 2 bit
>time delay on the signal."  Is this per byte? Are there results of
>testing to compare hardwired connections with C004-implemented connections?
>Any info and pointers to info are appreciated.  Thanks.

The delay I mesured was 175 nanoseconds (at 10 Mbit/s). This delay
has effect on every bit, that means every bit you put into a c004 has a
propagation delay of 1.75 bit periods befor it comes out of the c004
again.  The c004 only stores a single bit per channel, not a byte.
So every sigal (bit or byte) is delayed 1.75 bit times.
I think, the delay is caused by the signal regeneration, done by 5 times
oversamling if the link input signal (see inmos technical note 18, connecting
inmos lins, page 8).
If you use T800s or other transputers with the fast link protocol (overlapping
acknowledge), the delay of the C004 may slow down the data transmission
because the acknowledge comes too late so that the sender can't send
continously. I cannot measure this because I have only T414s and T212s.
This point was discussed in early 1989. I stored these postings, if you
need these old postings, please e-mail me directly.

--------------
Dieter Homeister, Universitaet Stuttgart,
Institut fuer parallele und verteilte Hoechstleistungsrechner (IPVR)
W7000 Stuttgart 1, Azenbergstr. 12, Tel 0711-121-1342, Germany
e-mail homeister@informatik.uni-stuttgart.dbp.de