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From: K312240@AEARN.BITNET (Klaus Kusche)
Newsgroups: comp.sys.transputer
Subject: Another Express problem
Message-ID: <9003192201.AA23405@tcgould.TN.CORNELL.EDU>
Date: 19 Mar 90 23:24:23 GMT
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X-Unparsable-Date: Mon, 19 Mar 90 23:01:33 SET


Dear Mailing List:

I finally got Strand-88 running on our PC-based transputer system.
(concerning my previous mail that the Express system which is behind
Strand seems to reset the link switches before loading the system:
It really does, I had to patch 'exkload', but now everything works
fine...).

However, I'm very frustrated with the topologies that Strand is able to
run on:
* We were not able to use any of the predefined Express topology
  classes 'torus' or 'hypercube', we had to classify every topology
  as 'general' (this could also be a lack of documentation).
* Given that, *any* (really, no exception!) topology containing a
  circle deadlocked sooner or later: Some during 'exkload' or 'topinit',
  the remaining ones during the Strand bootstrap. We never reached the
  Strand prompt.

So, only tree topologies remain. However, again there was a problem:
* In the Express topology file, it must be specified for each node
  which node is responsible for resetting this node, and if this node
  is connected to the system or the subsystem control lines of the node
  resetting it.
* 'exkload' insists that there is a direct link connection between any
  nodes whose reset signals are connected.
* 'exkload' also insists that each node resets at most one node via
  system reset, and at most one node via subsystem reset.
* Hence, by definition it is not possible (and 'exkload' strictly
  enforces that definition) to have any topology which contains a
  transputer being the common root of three independent subtopologies
  (ternary trees, which would be the most natural trees for transputers,
  are the most important examples of such impossible topologies):
  + The root of one of those subtopologies is reset by this transputer
    using the system reset ('down' in Inmos terminology).
  + The root of the second subtopology is also reset by this transputer
    using the subsytem reset.
  + However, there is no legal choice for the reset of the third
    subtopology: The only transputer it is connected to by link has no
    more unused reset outputs, and resets not going along a link are
    not allowed.
To increase confusion, 'cnftool' simply hangs on such topologies
without any message, rebooting the PC is the only way out...

Needless to say, our hardware of course does allow such configurations:
All transputers are controlled by a single reset...

To sum up: For two different reasons, it was impossible for us up to
now to run Strand on any topologies which are not variations of binary
trees (the pipeline being a special case of this).

Did anyone manage to get more than this?

P.S.: Some people asked what version of Express we use. It is
impossible to tell that! The only thing I can tell is that it is the
version which is part of Strand, and that some files contain the string
'August 1988'. However, I scanned all the binaries: No copyright, no
date, no version number!!! (have you ever seen such a software?)

************************************************************************
* Klaus Kusche                                                         *
* Research Institute for Symbolic Computation                          *
* Johannes Kepler University           Tel: +43 7236 3231 67           *
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*                                                                      *
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