Newsgroups:  comp.sys.transputer
From: co@buck.ac.uk (Carew Oladapo)
Subject: Re-Clarification needed for T800 transputer and OCCAM
Organization: University of Buckingham
Date: Mon, 11 Apr 94 10:00:30 GMT
Message-ID: <1994Apr11.100030.26838@buck.ac.uk>

Andy Rabagliati <andyr@wizzy.com> in his article writes :
>
>Actually the T800 overlapped acknowledge helps the unidirectional link
>speed rather than the bidirectional speed.
>
>I think that bidirectional speed is about the same, while the
>unidirectional speed climbs from about 1.5 (??) to 1.7Mbytes.

I have re-checked the speed settings for data transfer over transputer 
links for the IMS T800. It shows that data transfer using the bidirectional
link is faster than using the unidirectional link. This is due  to the 
implementation of the acknowledgement (such that the transmitter can receive 
the ACK before all the data packet is transmitted, and can transmit the next 
data packet immediately, i.e an overlap). Naturally, one would expect as Andy 
says, that this would favour unidirectional transmission of data, but INMOS 
claims that by implementing the overlapping and including sufficient buffering 
in the link hardware, the IMS T800 more than double the transfer rate in 
bidirectional data transfer.

This is summarised in the table below :

 ---------------------------------------------------
 |  Link   |  Linkn  |  Mbits/sec |  Kbytes/sec    |
 | Special | Special |            |  Uni   |     Bi|
 |---------|---------|------------|--------|-------|
 |  0      |  0      |    10      |  910   | 1250  |
 |  0      |  1      |    5       |  450   | 670   |
 |  1      |  0      |    10      |  910   | 1250  |
 |  1      |  1      |    20      | 1740   | 2350  |
 ---------------------------------------------------

The Link and Linkn special are used to set the link speeds. As shown in the
table above, the IMS T800 links support the standard communication speeds of
10 Mbits per second. In addition, these can be used at 5 or 20 Mbits per
second.
 Note : These data rates were quoted by INMOS based on internal memory, and
        will be affected by a factor depending on the number of external
        memory accesses and the length of the external memory access.


Cheers !
dapo.
-- 
/*****************************************************************************\
*									      *
* Oladapo Carew                                          < co@buck.ac.uk >    *
* Computer Science Department						      *
* University Of Buckingham, Buckingham, MK18 1EG, UK			      *
*									      *
*									      *
\******************************************************************************/


