Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!uwvax!astroatc!nicmad!madnix!rat
From: rat@madnix.UUCP (David Douthitt)
Newsgroups: comp.sys.apple
Subject: Re: Interrupt handling with a modem in CP/M
Message-ID: <741@madnix.UUCP>
Date: 23 Jul 89 02:55:16 GMT
Reply-To: rat@madnix.UUCP (David Douthitt)
Distribution: usa
Organization: ARP Software, Madison, WI
Lines: 49


Brian Willoughby (brianw@microsoft.UUCP) wrote:
|
| In article <1622@sactoh0|  ianj@sactoh0 (Ian R. Justman) writes:
| |
| | I need some help with writing a driver for a communications program
| | when using CP/M.  ...
| | I wrote an interrupt handling routine which is activated when a
| | character comes in and shoves the character into a circular buffer
| | within the driver space (it is 256 characters long, BTW...).  Even
| | with that in place, I still lose characters ...
| 
| Try doubling the circular buffer size and rewriting the interrupt
| routine.
| How does the interrupt routine handle buffer full condiitions?  Are you
| detecting when the buffer fills?  My interrupt routines increment a LOST
| count every time a new character interrupt tries to add a character to a
| full buffer.  Then, when my program is running, I can check this value
| and print an error message showing how many characters were lost.  If I
| see the error message, this is a sure sign that I need to increase the
| buffer size for that application.

One other thing is what CP/M card you're using.  If you use the PCPI
Applicard running at 6MHz, unless I'm mistaken, the Apple's 6502 (which
handles the I/O) can't keep up with the Z80.

This trouble could also be apparent in the Microsoft Z80 card.  You
should also make sure that your interrupt handler is behaving properly:

	1]  Do you detect buffer full?

	2]  Do you detect buffer empty?

	3]  Is your interrupt handler small and fast?  .. you could
	    be losing characters due to your handler being too slow..

	4]  Are you turning interrupts off at the appropriate point?
	    .. otherwise you might have one interrupt clobbering another
	    with disastrous results..

Hope these help..

	[david]

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