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=-1.9 required=5.0 tests=BAYES_00 autolearn=ham
	autolearn_force=no version=3.4.4
X-Google-Thread: 103376,7bb6fcf19a817eb0
X-Google-Attributes: gid103376,public
X-Google-Language: ENGLISH,ASCII-7-bit
Path: 
 g2news1.google.com!news2.google.com!newsfeed.gamma.ru!Gamma.RU!colt.net!peer-uk.news.demon.net!kibo.news.demon.net!news.demon.co.uk!demon!not-for-mail
From: Simon Wright <simon@pushface.org>
Newsgroups: comp.lang.ada
Subject: Re: tasking design for keylock
Date: Fri, 03 Mar 2006 20:48:52 +0000
Organization: Pushface
Message-ID: <m2bqwn6yq3.fsf@grendel.local>
References: <1141389368.420323.184550@v46g2000cwv.googlegroups.com>
NNTP-Posting-Host: pogner.demon.co.uk
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
X-Trace: news.demon.co.uk 1141418927 17255 62.49.19.209 (3 Mar 2006 20:48:47
 GMT)
X-Complaints-To: abuse@demon.net
NNTP-Posting-Date: Fri, 3 Mar 2006 20:48:47 +0000 (UTC)
Cancel-Lock: sha1:ijSVfaAxi4ik0CPTLisfyx3SGo4=
User-Agent: Gnus/5.11 (Gnus v5.11) Emacs/22.0.50 (darwin)
Xref: g2news1.google.com comp.lang.ada:3258
Date: 2006-03-03T20:48:52+00:00
List-Id: <comp.lang.ada>

"Rolf" <rolf.ebert_nospam_@gmx.net> writes:

> The following problem arose when I was thinking about the design for a
> minimal tasking runtime system.
>
> Many doors are locked by electronic keylocks where one has to type four
> correct keys on a small keyboard (mostly 0 .. 9, *, #) before the lock
> is opened. Now there are requirements
>
> - that the time between the key presses must not exceed 0.5 seconds,
> - and that after the 4th correct key you must not type any key at all
> for at least 0.5 seconds.
>
> How do you model the timing requirements using Ada tasking? (I can
> attach the h/w interrupt from the key press to a protected procedure,
> but I don't know how to proceed from there, i.e. how to cancel or serve
> a timed entry call now)

I may have misunderstood (and I may have got protected types wrong),
but .. assuming the interrupt handling PO is like

protected Interrupt_Handler is
   entry Read_Key (K : out Key);
   entry Handler;
   pragma Interrupt_Handler (Handler);
private
   ...
end Interrupt_Handler;

where Read_Key is released by the Handler entry, then you could

select
   Interrupt_Handler.Read_Key (K);
or
   delay 0.5;
   --  deal with missed input opportunity
end select;

--  repeat the above 3 times more

select
   Interrupt_Handler.Read_Key (K);
   --  deal with additional input
or
   delay 0.5;
   --  now we have the correct number of characters and no more
end select;


Thad doesn't handle multiple keypresses so close together that they
bunch up in the PO, of course.