Path: utzoo!utgpu!news-server.csri.toronto.edu!helios.physics.utoronto.ca!ists!sgl!georg
From: georg@sgl (Georg Feil)
Newsgroups: comp.realtime
Subject: Re: What is the future of realtime and RISC?
Message-ID: <23089@ists.ists.ca>
Date: 17 May 91 15:44:37 GMT
References: <1991May15.210430.1134@nbc1.ge.com>
Sender: news@ists.ists.ca
Lines: 50

scott@nbc1.ge.com (Scott Barman) writes:
>+ With the rise of RISC over the last few years why hasn't it taken a
>hold in the realtime world?

Some reasons I can think of (feel free to argue):

-Real-time systems are often required to be extremely reliable, as failures
   can mean expensive equipment damage (process control) or even loss of
   life (critical aircraft and spacecraft systems). Therefore implementors
   are simply more cautious about following the latest trend of doing things.
   They know their old methods work. NASA and the US space program are a good
   example: they were flying core memory around long after the rest of the
   world had moved on to semiconductors.

-For those who do real-time programming in assembler, working with a RISC
   processor is probably more painful.

-RISC cross-compilers are not quite as numerous as those for 680x0.

-Fewer real-time kernels are available. I assume this is due to the
   work involved in porting them. It is my impression real-time kernels
   are traditionally coded in assembler, although this is probably an 
   incorrect assumption these days.

-RISC code sizes are greater than CISC, impacting those with limited EPROM
   or RAM space requirements.

-RISC can have longer context-switch times with more registers to save.

-With RISC fanciness such as delayed branches and greater reliance on 
   caching, the hard determinism required in many real-time applications 
   is more difficult to come by.

>+ What is the future of realtime and RISC?

Probably the same as the future of RISC in general, only delayed by a number
of years. However, this applies mainly to "high-power" real-time applications.
Those small embedded systems which don't need additional CPU speed will see
no reason to switch to RISC. Witness the large number of 8051's out there
and still being designed into new systems. The 8-bit microcontroller market
is the largest of any class, and is likely to remain that way. For the same
reasons, we'll be seeing 680x0's for a long time to come.


Georg.
--
Georg Feil                                 Internet: georg@sgl.ists.ca
Space Geodynamics Laboratory               (toronto.edu address no longer valid)
ISTS, 2700 Steeles Ave West                   Phone: (416) 665-5458
Toronto, Ontario                                Fax: (416) 660-1422