Newsgroups: comp.sys.transputer
From: Brian.Oneill@ntu.ac.uk
Subject: Re: About virtual channels
Organization: Deja News - The Leader in Internet Discussion
Date: Fri, 12 Jun 1998 16:44:06 GMT
Message-ID: <6lrlsm$psl$1@nnrp1.dejanews.com>



On 11 June 1998 Andy Rabagliati wrote:

> The innovation of the T9000 VCP is :-
>
> A)  Multiplexing of channels across the link
>     (which SARNet appears to do)
>
> B)  Packetising of such transfers, so that true time-sharing takes place,
>     as Jan Vorbrueggen described,
>     (which, from your description above, SARNet does not do)
>     (this would mean that a large transfer scheduled ahead of a small one
>      would hold up the small one)
>

True enough, our hardware can't do this, but it is easy performed by
software. Obviously the overheads would increase with the inclusion of such
packetisation relative to the size of message and size of packets sent.  One
advantage of an FPGA design is that it is reconfigurable and therefore
customisation to vary the balance of hardware/software for VCP is possible.

> C)  Header addition/deletion, which in conjunction with the wormhole
>     through-router (which relies on the packetisation) allows
>     arbitrarily complex routing schemes, possibly all handled with
>     the worm-hole throughrouter.
>
> The overhead is slightly more for the setup, but the VCP engine does
> all the rest, including packetisation and rescheduling.
>

The SARNet routing protocol is set so that there is a fix length header,
which includes both routing and VCP information.  The header is processes by
the SARNet system and node interface such that only the VCP information is
received and supplied on the interrupt.  This allows a point to point connect
between any node in the complex routing topology of the system with the
identical message initialisation procedure.


Brian  O'Neill
Nottingham Trent University
E-mail: Brian.ONeill@ntu.ac.uk
http: //www.ntu.ac.uk/eee/research/parallel/




-----== Posted via Deja News, The Leader in Internet Discussion ==-----
http://www.dejanews.com/   Now offering spam-free web-based newsreading