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From: gday@digigw.digital.co.jp (Gordon Day)
Newsgroups: comp.os.msdos.programmer
Subject: Communicating With Resident Programs
Keywords: driver, TSR, interrupt vectors
Message-ID: <679@digigw.digital.co.jp>
Date: 1 Oct 90 07:16:34 GMT
Organization: Digital Electronics Corp., Osaka, Japan
Lines: 22

Could somebody suggest the best way to communicate with a driver?  I have 
successfully implemented a block device driver, but I am at a loss as to the
best way to communicate with it from a transient program.  I have come up 
with three ideas, both with advantages and disadvantages:

1. Search through available user interrupts (0x61 - 0x67) for a free one and
use that.
	Advantages: easy
	Disadvantages: All may be used, a poor program may override the vector.

2. Use Multiplex Interrupt (0x2f) 
	Advantages: easy, better than #1 for safety
	Disadvantages: ID value may already be used (although smaller odds than #1)

3. Chain through device headers searching for signature
	Advantages: almost 0 chance of interference ~length(signature)^256 odds,
	Disavantages: requires undocumented system call, access to o/s structures.


Any help regarding this matter would be appreciated (I'm swaying between 2 & 3)

Gordon W. Day