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From: stever@videovax.UUCP (Steven E. Rice)
Newsgroups: net.micro.amiga
Subject: Re: Clarifications for the Ultra Fast Timer
Message-ID: <1728@videovax.UUCP>
Date: Thu, 29-May-86 11:39:42 EDT
Article-I.D.: videovax.1728
Posted: Thu May 29 11:39:42 1986
Date-Received: Tue, 3-Jun-86 20:52:41 EDT
References: <724@watcgl.UUCP>
Reply-To: stever@videovax.UUCP (Steven E. Rice)
Distribution: net
Organization: Tektronix, Comm Group, TV R&D
Lines: 41

In article <724@watcgl.UUCP>, Flynn D. Fishman (fdfishman@watcgl.UUCP) writes:

> The  1 +/- uS accuraccy is what the boss ordered :-) I was hired by the
> lab here to work on a project with the psycology department.  The prof.
> is doing an experiment on the analysis of what is seen by the brain (more or
> less). In his experiment he shows the subject a blob (what else) with a dot
> somewhere near it.  The user (guinne pig) is then expected to 
> press a button depending on the position of the dot (i.e. inside or outside
> of the blob). It is this period between when the blob is shown and the user
> press the button that I need accurately timed.
 
> Unforunately we are relying on a human input so the time spand can
> be several seconds,  I can not see the time being more than 20 seconds
> though, (unless the user is a real loser :-)
 
> The timing will be in bursts.  How long between the Blob is shown and the
> user presses a button, I will then draw the next blob (and perform other
> calculations) and then start the timer again.

It sounds as if the specification is unrealistic. . .  Given normal
human reaction times, the 60 Hz tick should be accurate enough!  However,
remembering the old maxim that "the boss may not always be right, but he's
always the boss," charge ahead.

A suggestion, though.  Put the timing into a separate unit (e.g., a
single-board computer with RS-232C interface, or the like).  If you use a
very high baud rate for the communication between the AMIGA and the SBC,
the starting jitter in the timing will be relatively small (of course,
send just a single character to cause it to start timing).  Connect
the user pushbutton to the SBC, and have that stop the timer.  Then the
AMIGA can send a request to the SBC (some other character) to get a string
containing the timing information.

It is in general very difficult to combine multitasking (with its high
overhead) with fast real-time response.  In cases such as the one you
have, separating the functions will be much more effective.

					Steve Rice

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