From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=-0.8 required=5.0 tests=BAYES_00,INVALID_DATE
	autolearn=no autolearn_force=no version=3.4.4
X-Google-Language: ENGLISH,ASCII-7-bit
X-Google-Thread: 103376,6e12ca1eee1236db
X-Google-Attributes: gid103376,public
X-Google-ArrivalTime: 1995-01-19 22:08:24 PST
Path: 
 pad-thai.cam.ov.com!bloom-beacon.mit.edu!news.media.mit.edu!grapevine.lcs.mit.edu!uhog.mit.edu!news.mathworks.com!news.duke.edu!eff!blanket.mitre.org!linus.mitre.org!spectre!eachus
From: eachus@spectre.mitre.org (Robert I. Eachus)
Newsgroups: comp.lang.ada
Subject: Re: ADA-9x done? Any good PC compilers?
Date: 19 Jan 1995 19:08:47 GMT
Organization: The Mitre Corp., Bedford, MA.
Message-ID: <EACHUS.95Jan19140847@spectre.mitre.org>
References: <1995Jan11.154250@clstac> <3f49k3$kfp@gnat.cs.nyu.edu>
	<3f614s$5ie@news.ycc.yale.edu> <3f9m5u$rc8@gnat.cs.nyu.edu>
	<EACHUS.95Jan17120531@spectre.mitre.org> <3fk7j7$ld5@gnat.cs.nyu.edu>
NNTP-Posting-Host: spectre.mitre.org
In-reply-to: dewar@cs.nyu.edu's message of 18 Jan 1995 18:17:58 -0500
Date: 1995-01-19T19:08:47+00:00
List-Id: <comp.lang.ada>


In article <3fk7j7$ld5@gnat.cs.nyu.edu> dewar@cs.nyu.edu (Robert Dewar) writes:

 > I was talking about when a delay expires, this has nothing to do with the
 > required preemption by a higher priority task!
 > (responding to Eachus' note on my note about infinite delays)

    RM83 9.6(1): The execution of a delay statement evaluates the
simple expression, and suspends further execution...for at least the
duration specified by the resulting value.

    RM83 9.8(4): If two tasks with different priorities are both
eligible for execution...then it cannot be the case that the task with
the lower priority is executing while the task with the higher
priority is not.

    The first creates a requirement that the delay must be at least
that specified in the expression, the second paragraph adds a
requirement which, on a single processor system, simplifies to: "The
highest priority eligible task must be executing, in case of ties, the
selection among the tied set is implemetation dependent."  Paragraph
9.6(1) does not conflict with or supercede 9.8(4).  They work
together.  Paragraph 9.6(1) declares certain tasks ineligible until
the delay expires, 9.8(4) specifies requirements with respect to
eligible tasks.

    I think you (Robert) perfectly well understand that the only
freedom granted by 9.6 with respect to 9.8 is that the clock for
interrupts need not be maintained to DURATION'SMALL resolution. The
resolution is found instead in SYSTEM.TICK.  If you want to validate a
system where SYSTEM.TICK = DURATION'LAST, fine.  But that still won't
allow infinite prolongation of delays.

--

					Robert I. Eachus

with Standard_Disclaimer;
use  Standard_Disclaimer;
function Message (Text: in Clever_Ideas) return Better_Ideas is...