Newsgroups: comp.sys.transputer
From: paul@walker.demon.co.uk (Paul Walker)
Subject: Re: Request for information on DMA controllers
Organization: Paul Walker Consultancy
Date: Thu, 17 Nov 1994 07:53:14 +0000
Message-ID: <785058794snz@walker.demon.co.uk>

In article <1994Nov14.140831.1@ntuvax.ntu.ac.sg>
           asskleong@ntuvax.ntu.ac.sg  writes:

>> It could be easier to build your own with PLDs?
>> 
>        Just something came into mind, instead of PLDs how about FPGA chips
>such as XILINK (sp ?) ?

Yes, if you use descent tools for the Xilinx development. Which means either
the Occam to Xilinx done by Ian Page and his group at Oxford, or (very much
second best) one of the VHDL to FPGA routes, of which Cypress's with
the Quicklogic FPGAs is probably best. You may get the performance you
need with FPGAs, but performance of PALs/PLDs is much more predictable.
>
>        In our case, a single-channel DMA controllers will be good enough.
>
But your wanting a simple fast interface to DRAM on both sides is different
from the normal of interfacing to a bus such as ISA or PCI. So IMHO you would
be better designing your own. The single channel makes it easier.

>        We intend to use the DMA controllers to transfer data from the
>external DRAM of the transputer to a pool of memory which can be shared
>by other processing elements such as transputers, 80486s, and the like.
>We think one-channel DMA controller should be sufficient.
>
>        At the moment we are planning for two banks (each 1MB) for the
>external DRAM for each transputer and four banks (each 512 KB) for the
>pool of memory.
>
>        The transfer rate, ideally should be approximately 10.5 MB per
>second.

With the memory 32-bits wide, this speed should not be too much of a problem.
If you were to want the DMA at this speed only to use say 20% of the available
memory bandwidth, you would need it to go rather faster and probably use
page mode during a DMA burst.

A FIFO between the two RAMs would make life easier.

>
>Sincerely,
>Soon-Khing Leong
>
 Best wishes for the develpoment.
 
 Paul Walker                             "Making Connections"
 +44 1275 844 864              paul@walker.demon.co.uk


