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From: cramer@kontron.UUCP
Newsgroups: comp.sys.ibm.pc
Subject: Re: Need help with MS-DOS 3.1 and COM1 device
Message-ID: <1342@kontron.UUCP>
Date: Thu, 29-Jan-87 12:30:28 EST
Article-I.D.: kontron.1342
Posted: Thu Jan 29 12:30:28 1987
Date-Received: Sat, 31-Jan-87 02:11:18 EST
References: <3281@hplabs.hplabs.UUCP>
Organization: Kontron Electronics, Mt. View, CA
Lines: 49

> I have written a DVI to HP LaserJet+ Driver that runs under both Unix
> and MS/PC-DOS.  Unfortunately, I have discovered a problem either in the
> Aztec C Run-time support, (which they deny), or a problem with MS-DOS,
> (a misunderstanding, no doubt).  I am running MS-DOS V3.1 and am
> putc()ing characters to a stream that was successfully opened via
> fopen() for "w" access to "COM1".  I check the returned pointer for NULL
> and guaranteed fopen()s success.  However, after writing BUFSIZ
> characters, putc() returns EOF.  I traced the run-time code and found
> that a DOS write handle was returning less bytes than were written.  The
> Manx code gave up the ghost and died.  I rewrote the routine to loop
> through write() calls until the entire buffer had been written.  When I
> compiled and ran the code, MS-DOS continually and repeatedly refused to
> accept any more data to the fopen()ed handle. 
> 
> Next, instead of directing output to COM1 I started sending the data to
> the disk file "laserjet.dat" and was pleased to find that the data was
> indeed there and correct.  I then copied the file to COM1 via the
> command:
> 
> 	COPY LASERJET.DAT COM1
> 
> and was disturbed to find that the file did not print on the LaserJet. 
> After reading the DOS manual I discovered that the /B option for COPY
> would probably correct the problem.  I used it and it did! OK, the
> question is, "WHAT MS-DOS FUNCTION CALL DID COPY MAKE TO CAUSE THE FILE
> TO PRINT?" It sounds like the handle must be placed in raw mode, or
> something synonymous.  Unfortunately, I do not know how to do this, and
> the programmer's manual for MS-DOS is not too helpful.  Any help would
> be appreciated.  Writing to a temporary file and then system()ing COPY
> is not an acceptable solution.  Many thanks in advance.
> 
> 	Dave Richards at Hewlett-Packard Labs (drichard@hplabs)

Assume the Aztec library is bad.  I have programs that write to an Apple
LaserWriter using COM1 from Microsoft C using fopen and printf and the only
problem I have is that the LaserWriter starts losing data eventually
because PC-DOS doesn't support XON/XOFF.

My experiences with Aztec C libraries have been pretty disheartening.
I wrote a small program a couple of years ago using the Aztec C compiler
to read characters from the keyboard.  There are a number of characters
on the IBM keyboard that return two characters -- a NULL and then a second
character.  The Aztec compiler returned just the second byte, with no
indication that a NULL should be there also.  As a result, I was unable
to distinguish arrow keys from some of the letters.

That's when I went out and bought Microsoft C.

Clayton E. Cramer