🚀 go-pugleaf

 
James Pinakis asks:
 
>I'm interested in any references anyone may have on the C004.  In
>particular, has any work been done using C004s to dynamically
>reconfigure a transputer network according to workload distribution?
 
We have considered using C004 switches for dynamic switching during the
development of the Parsys SN1000 Series of transputer `Supernode'
machines. In order to reconfigure the switches in an efficient
manner, we have had to provide several other hardware features.
 
The main design target was to provide a link switching network that
would guarantee that any transputer network could be implemented in a
simple and predictable way. Some switching networks that have been
implemented in transputer systems are hard to analyse mathematically,
making the task of mapping a network onto the switch difficult. Even for
a static link network, non-deterministic algorithms requiring extensive
computation have been used but do not guarantee a result. Such an
approach is not suitable for supporting dynamic reconfiguration.
 
The switch architecture that was developed with our collaborators under
European ESPRIT project 1085 has the following features: transputers are
clustered together in Supernodes where all link switching is performed
by a single layer of switching. To connect two transputers within a
Supernode, a single switch setting command is required so that the links
may be connected quickly. In order to increase the number of transputers
that could be connected in this fashion above the limit of 32 for a
C004, a special switch chip was developed providing switching for 72
transputers.
 
For larger systems, several Supernodes may be connected together. A
three layer switch is used to minimize the number of switch setting
commands that have to be issued to make a connection. If a connection is
required between transputers in different nodes, the 72 way switches in
each Supernode are used to connect the transputers to inter-node links;
these two inter-node links may then be connected through a C004 in the
Inter-node Switch. This arrangement may be used to support over a
thousand transputers with a very simple switch setting algorithm that
guarantees that all possible transputer networks may be set up (see
Switching Networks For Transputer Links by D. Nicole et al. in the
Proceedings of the 8th Technical Meeting of the Occam User Group,
Sheffield, ed. J. Kerridge, 1988).
 
The 72 way switch is memory mapped on a Supernode Controller transputer,
while the Inter-node Switch is controlled through an array of T212
transputers that each control two C004 chips. This allows fast control
of all the switches within the system. Other C004 switches are used for
connecting to peripheral devices, but do not require high bandwidth
reconfiguration - these are driven by memory mapped link adapters on the
Supernode Controller transputer.
 
There is a disadvantage of using the C004 in a fully switched link
network. The C004 reset state has all outputs disabled, so all links are
isolated. Before communications can take place with the outside world,
it is necessary to configure the C004s, either with boot-from-ROM code
on the switch controllers or by providing a state machine that pumps
commands into the C004s after reset. It would be useful to have some
default connection options present in future C004s, or a non-hand-shaken
configuration pin that can be used to pump in an initialization state
after reset.
 
Before dynamic switching can be performed, the two ends of a link must
be placed in the idle state to avoid message corruption. The Supernode
has a separate communications network, called the Control Bus, to
provide support for this. Before the Switch Controller alters a link
network, it can suspend communications on the affected links by passing
messages on the Control Bus to all affected transputers. The worker
transputers may also request switch changes by passing messages to the
Switch Controller. The Control Bus has additional facilities to allow
synchronization between multiple transputers. When a group of processors
have all reached a certain state, a message can be passed to the Switch
Controller to indicate that all of the transputers have finished
communication over a link network. The Switch Controller can then
rearrange the network and signal that communications may resume. This
allows a PLACED PAR within SEQ construct in Occam to be supported
efficiently and is useful for processor communications within a
multi-processor Unix environment.
 
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Trevor Carden            (01 or +44 1) 848 6504
Parsys Ltd.,
THORN EMI CRL
Dawley Road, Hayes,
Middlesex, UB3 1HH, England
 
Trevor_Carden_THORN_EMI_CRL%eurokom.ucd.irl@euroies.uucp