Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!rice!uupsi!cci632!ritcsh!ultb!axi0349
From: axi0349@isc.rit.edu (A.X. Ivasyuk )
Newsgroups: comp.sys.apple2
Subject: Re: CPU speed detection
Summary: Yes, there is VBL on the //c
Message-ID: <1990Dec6.180741.2522@isc.rit.edu>
Date: 6 Dec 90 18:07:41 GMT
References: <9012052301.AA15585@cs-sun-fsa.cpsc.ucalgary.ca>
Organization: Rochester Institute of Technology
Lines: 40

In article <9012052301.AA15585@cs-sun-fsa.cpsc.ucalgary.ca>, barcan@CPSC.UCALGARY.CA (Davor Barcan) writes:
> I'm currently working on an application that is timing dependent.

<< stuff deleted>>

> the CPU.  One method that I can think of is by using the VBL and
> keeping a counter until the VBL changes again.  Would this be an
> accurate method?  I'd probably have to keep a very big counter
> a very big counter if one happens to be running at 10 Mhz,
> assuming that this is an effective method.

This should be quite effective, because VBL is guaranteed to change 60
times per second on North American standard Apples.

> There's a further complication in that the VBL is handled
> differently on a //e and a GS, and as far as I know the //c
> doesn't have a VBL (or at least one that works).  Does anyone

The //e has a VBL register at $C019, I believe, which tells the current
state of the VBL.  Bit seven indicates whether you are actually in the
middle of VBL interrupt.  The //gs has a different system, but I don't
know about the //gs, since I don't have access to one.  On my //c,
however, you can have the (built-in) mouse card interrupt your program
every time there is a VBL interrupt and proceed to run an interrupt
routine.  The easiest was to install interrupt routines is through the
ProDOS system calls.  I believe the //e mouse card and the gs mouse
firmware behave in the same way as the //c.  There is a program called
Daemon which is, I believe, shareware, which runs stuff in the
background based on the VBL.  It should be available on FTP and on the
listserv at APPLE2-L (listserv@brownvm.brown.edu).

> Davor Barcan
> barcan@cpsc.UCalgary.CA
> University of Calgary

@@@@  @@@@@ @@@@@         Anatoly Ivasyuk             @@@   @@@  @   @
@   @   @     @      (axi0349@ultb.isc.rit.edu)      @   @ @     @   @
@@@@    @     @        Computer Science House        @      @@@  @@@@@
@  @    @     @   Rochester Institute of Technology  @   @     @ @   @
@   @ @@@@@   @      "If all else fails, RTFM."       @@@   @@@  @   @