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From: brendan@batserver.cs.uq.oz.au (Brendan Mahony)
Newsgroups: comp.realtime
Subject: Re: Software primitives for real-time programming languages
Keywords: Languages
Message-ID: <5003@uqcspe.cs.uq.oz.au>
Date: 26 Sep 90 00:37:03 GMT
References: <12712@cs.utexas.edu> <1424@umriscc.isc.umr.edu> <39180@shemp.CS.UCLA.EDU> <225@srchtec.UUCP>
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johnb@srchtec.UUCP (John T. Baldwin) writes:

>I agree with the statement that
>assembly coding is typically less "reliable" than other forms of coding;
>yet I disagree that it is inappropriate for RT.

	It may be a little hard to meet a timing requirement if your are
	completely malfunctioning. Real-time reliability is a proper
	extension of software engineering reliability, not an orthogonal
	issue.

>I would rather not
>resort to assembler, but given certain task/hardware pairs, you only have
>a certain time rate of execution ("performance"), and it may be that the
>only way to meet the RT constraints of your given task on the specified
>hardware is to use assembler.   :-{

	Probably the compiler writer knows more about extracting "juice"
	out of the processor than most programmers, but I will ignore
	that fact. Programming in assembly is no theoretical impediment
	to "reliable" programming, but it does mean one or
	two more refinement steps, and a much larger source code to
	reason about. Hence I would expect it to be much more expensive,
	with fairly little return in performance over a good compiler.
	You pays ya money ...

	Ian Hayes has just walked in and suggested that a language in which
	you could make timing demands on the compiled code would be
	useful. For example
		a := exp | /\ t < 4 microsecs;
	Inability to comply would be flagged as a "syntax" error, along
	the lines of type mismatches etc.

	Does anyone know of any proposals along these lines?

--
Brendan Mahony                   | brendan@batserver.cs.uq.oz       
Department of Computer Science   | heretic: someone who disgrees with you
University of Queensland         | about something neither of you knows
Australia                        | anything about.