Date   : Tue, 23 Aug 1994 09:34:06 EST
From   : Stephen Quan <quan@...>
Subject: Re: xbeeb updated on ftp.pipex.net

> James Bonfield wrote:
> 
> > Tim M. writes:
> > 
> > >The 'problem' is that Config.h assumes it is on a litle endian
> > >machine, and defines LITTLE_ENDIAN. This breaks ReadWordAtPC on big
> > >endian machines. However you do mention in the INSTALL file that the
> > >LITTLE_ENDIAN flag may have to be changed. It might be worth putting
> > >in a little bit more detail so that more people notice it....
> > 
> > Even on a little endian machine (Alpha) defining LITTLE_ENDIAN broke
> > things for me!

What I have in my emulator (in C), is the following typedef's

  typedef unsigned char  byte;
  typedef unsigned short word;

This defines 8-bit and 16-bit storage classes.

To allow for MS-DOS support (Borland C), I have typedef and #defines
in my bbc_defs.h module, listed below.  By using these types I can
freely move my code between UNIX and DOS and worry less about the
64K boundaries (I only partially slow the problem).

> #ifndef BBC_DEFS_H
> #define BBC_DEFS_H
> 
> #ifdef _DOS_
> /* The IBM-PC has unusual ways for using memory beyond 64K. */
> #include <alloc.h>
> #define Malloc farmalloc
> #define Free   farfree
> #define charfar           char  far
> #define shortfar          short far
> #define charptr           char  far *
> #define shortptr          short far *
> #define byte     unsigned char
> #define word     unsigned short
> #define bytefar  unsigned char  far
> #define wordfar  unsigned short far
> #define byteptr  unsigned char  far *
> #define wordptr  unsigned short far *
> #endif
> 
> #ifdef _UNIX_
> /* UNIX versions of the macros. */
> #include <stdlib.h>
> #define Malloc malloc
> #define Free   free
> #define charfar           char
> #define shortfar          short
> #define charptr           char  *
> #define shortptr          short *
> #define byte     unsigned char
> #define word     unsigned short
> #define bytefar  unsigned char
> #define wordfar  unsigned short
> #define byteptr  unsigned char  *
> #define wordptr  unsigned short *
> #endif
> 
> #endif

With the above #define, a 64K memory allocation is possible

    memory = (byteptr *) Malloc(0x10000);

And I can define far compatible arrays

    bytefar osrom[0x4000];

However, this does not completely oblitherate the 64K boundary, as
the following is not legal.

    bytefar memory[0x10000];

The compiler rejects it, eventhough I am able to allocate this memory
at run-time.
-- 
Stephen Quan (quan@...                 ), SysAdmin, Analyst/Programmer.
Centre for Spatial Information Studies, University of Tasmania, Hobart.
GPO BOX 252C, Australia, 7001.  Local Tel: (002) 202898 Fax: (002) 240282
International Callers use +6102 instead of (002).