Path: utzoo!attcan!uunet!husc6!rutgers!bellcore!faline!thumper!rtm1
From: rtm1@thumper.bellcore.com (Ravi Masand)
Newsgroups: comp.sys.transputer
Subject: Re: What makes Transputer interesting
Message-ID: <1389@thumper.bellcore.com>
Date: 16 Nov 88 20:11:39 GMT
Reply-To: rtm1@thumper.UUCP (Ravi Masand)
Organization: Bellcore MRE
Lines: 79

In article <> josef@ugun21.UUCP writes:
>
>What distinguishes a Transputer from any other processor, especially if
>I take a, let's say 68030 or 32532, add 4 communication channels
>and write software to do processor-processor communication?
>What makes a Transputer so interesting?
>
>		Josef Moellers
>

'Interesting' is a subjective characteristic. I personally feel that the 
transputer is interesting because, atleast from a hardware developer's
viewpoint it offers a lot of bang for the design effort.

Lets start with your 68030 alongwith its four communication channels - to match
the transputer these links need to operate at 10 Mbps and contending with
these communication devices is no cakewalk - both in terms of H/W and S/W

The transputer provides a multitasking kernel built right in the microcode.
The multitasking processes use channels for interprocess communication - and
these channels can be implemented either with memory exchanges or over the
serial links. This can be made transparent to the application programmer. What
this does is that it allows initial development and use over a lesser number
of transputer and at a later time, if so desired, performance can be enhanced
and almost linear speedup achieved, by increasing the number of transputers
in the system and redistributing processes.
As far as the multitasking is concerned, all instructions use a register stack
(on chip) which is valid only for the duration of the instruction. This makes
context switching extremely fast.

This philosophy of integrating the links right into the kernel pays divedends
in another manner. The transputer is capable of booting itself right from 
the links. This implies that in a multiple processor system only one transputer
is required to have a ROM. The others will be perfectly content with a simple
RAM subsystem.

Another hardware facility provided is that of a DRAM controller built right
into the chip. This simplifies DRAM system design considerably.

Also provided in hardware is a floating point unit. As to how it compares with
the 80387 and Motorola's FPU I don't know. Reasonably well I'd suspect. 

Another hardware goody provided is on-chip memory. This is either 2k or 4k
depending on the CPU (T414 or T800 resp). While not much in itself it can
be used for code optimization as instructions running out of this on chip RAM
run a lot faster than from external RAM.

And the final hardware goody provided is an on chip frequency multiplier. 
This means that the different speed versions all take in 5 MHz clocks and 
multiply it appropriately to generate 20/25/30 Mhz. Thus these high frequencies
are restricted to within the chip.

These are all the hardware pluses I can think of. There probably are some
more.

Far as the software is concerned - Inmos claims that a high percentage (~70?) of
the instructions can be coded in one byte. I have looked at the instruction
encoding philosophy and found it to be impressive. If you are at all interested
in CPU architectures you really should look at it. It is, to say the very least,
'Interesting'.
I haven't really had any experience with the software but soon will have some.
But probably not with Occam.

Please keep in mind that I am no transpu-phile and Inmos has no say in my 
material well being. I have simply worked with the CPU for a little while and
was favorably impressed. Furthermore I don't think that the transputer is
'better' than the 68030 or vice versa. For a given application one or the
other may be more appropriate and for still other applications a Z-80/8085
would be clearly more desirable :-).

Questions: Has anyone out there worked with the transputer in  a language other
than Occam ? How has it worked out ? Is Occam really mandatory to use the
CPU to its fullest ? And anyone know of a good book/reference to pick up
Occam in a hurry ??

Thats it. Cheers.
Ravi Masand
Bellcore
(201)-829-4593.