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From: frank@cavebbs.gen.nz (Frank van der Hulst)
Newsgroups: comp.os.msdos.programmer
Subject: Re: Serial line TSR - help needed please?
Keywords: serial TSR how nasty DOS stuff
Message-ID: <1990Dec25.094443.4925@cavebbs.gen.nz>
Date: 25 Dec 90 09:44:43 GMT
References: <6517@crash.cts.com>
Organization: The Cave MegaBBS, Public Access Usenet, Wellington, NZ
Lines: 21

In article <6517@crash.cts.com> alen@crash.cts.com (Alen Shapiro) writes:
>A friend of mine is having REAL trouble writing a TSR that reads a serial
>port (at interrupt time) and stores chars in memory until a NL is read,
>when it dumps the line to a file. The data rate is 300 baud max and
>max 80 char lines are received no more than once every 3 mins.

His major problem is how to write stuff to the disk -- DOS is *NOT* reentrant
so he shouldn't write to the disk if some other application is currently
calling DOS. There are several ways round this: catch all calls to DOS, setting
a flag on entry and exit, or else latch onto the DOS idle interrupt (INT 28h,
I think) which is called by DOS when its OK to call DOS.




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