Finding the MCGA in Quick C 2.01

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4 total messages Started by Julian Cowley Fri, 17 Aug 1990 04:51

#1909

Author: Julian Cowley
Date: Fri, 17 Aug 1990 04:51

29 lines
1390 bytes

I've just come over from comp.lang.c where this request drew a
blank expression from the members of the newsgroup.  What I'm
trying to do is access the MCGA screen at A000:0000.  Here was
my first attempt:

PutPixel (int x, int y, unsigned char c)
{
  unsigned char far *mem;

  FP_SEG (mem) = 0xa000;
  FP_OFF (mem) = 320 * y + x;

  *mem = c;		/* <-- this line gives a run-time error */
}

The commented line caused run-time error R6013: illegal far
pointer use.  (Unfortunately, I do not have the manuals to look
up the cause, even though this is a legitimate copy of Quick
C.)  The help page for the FP_* macros says that the macros
won't work under certain conditions in small and medium models,
but this happens in large model also.

So my question boils down to this: what is the cleanest way of
accessing an absolute address such as 0xa0000 in Quick C?

julian cowley
university of hawaii at manoa
julian@uhccux.uhcc.hawaii.edu
julian@uhccux.bitnet

Re: Finding the MCGA in Quick C 2.01

#1910

Author: David M. Read
Date: Fri, 17 Aug 1990 11:46

23 lines
1257 bytes

In article <> julian@uhccux.uhcc.Hawaii.Edu (Julian Cowley) writes:
>
>So my question boils down to this: what is the cleanest way of
>accessing an absolute address such as 0xa0000 in Quick C?
>

I don't know about QuickC for sure, but I have done the following
successfully in full-blown Microsoft C (5.1):

   unsigned char far *mem;

   mem = 0xA000:0000;
   *(mem + offset) = val;

where offset & val are self-explanatory.  I did this in order to 
do some direct screen writes to CGA ram, and everything worked just
fine, in all four memory models.

Good luck with it...

--
Dave Read                       | read@lampf.lanl.gov 
UT-Austin Nuclear Physics       | readdm@walt.cc.utexas.edu

Re: Finding the MCGA in Quick C 2.01

#1913

Author: William C. Marsh
Date: Fri, 17 Aug 1990 15:25

28 lines
1262 bytes

Lots of people post code that looks like:
>   unsigned char far *mem;
>
>   mem = 0xA000:0000;
>   *(mem + offset) = val;

Could we please stop using code that looks like this?  This is very unportable
to other 80x86 C compilers!  If you use the provided services in the compiler
(either MSC style or TurboC style) then there is a good chance it will work
elseware (Plus, it's easier to understand).

Examples (Using the above):

MSC:

	FP_SEG(mem) = 0xA000;
	FP_OFF(mem) = 0x0000;

TurboC:

	MK_FP(mem, 0xA000, 0x0000);

Bill
-- 
Bill Marsh, Naval Ocean Systems Center, San Diego, CA
{arpa,mil}net: bmarsh@cod.nosc.mil
uucp: {ihnp4,akgua,decvax,dcdwest,ucbvax}!sdcsvax!nosc!bmarsh
"If everything seems to be coming your way, you're probably in the wrong lane."

Re: Finding the MCGA in Quick C 2.01

#1951

Author: Jon Keck
Date: Tue, 21 Aug 1990 00:33

34 lines
1581 bytes

In article <2060@cod.NOSC.MIL> bmarsh@cod.nosc.mil.UUCP (William C. Marsh) writes:
>Lots of people post code that looks like:
>>   unsigned char far *mem;
>>
>>   mem = 0xA000:0000;
>>   *(mem + offset) = val;
>
>Could we please stop using code that looks like this?  This is very unportable
>to other 80x86 C compilers!  If you use the provided services in the compiler
>(either MSC style or TurboC style) then there is a good chance it will work
>elseware (Plus, it's easier to understand).
>
>Examples (Using the above):
>
>MSC:
>
>	FP_SEG(mem) = 0xA000;
>	FP_OFF(mem) = 0x0000;
>
>TurboC:
>
>	MK_FP(mem, 0xA000, 0x0000);

From the Turbo C 2.0 Reference Guide, p. 251, the syntax of the MK_FP 
macro is

	void far *MK_FP(unsigned seg, unsigned ofs);

 
-- 
John Keck INTERNET:keck@sea.com UUCP:...!ucsd!soledad!keck VOICE:619/581-6181
Systems Engineering Associates, 2204 Garnet Ave Suite 203, San Diego CA 92109
-----------------------------------------------------------------------------
 "Much speech leads inevitably to silence. Better to hold fast to the void."

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