/* callback.h - define callback functions for loadable modules */
#ifndef	_CALLBACK_H
#define	_CALLBACK_H

/*
	A loadable module is a 'C' source program which has been
	compiled under BC or TC using tiny model with -r save regs.

		bcc -mt -r source.c
		link source.obj,source.exe,source.map, cs.lib
		rem note that c0t.obj is NOT linked in
		exe2bin source.exe source.bin

		copy source.bin sys:usr\charon\spool

	Tiny model programs have only one segment, DS=CS=SS

	The data segment is composed of static initialized data
	and unititialized data (BSS).

	Charon runs multiple copies of the module by generating a unique
	data/stack area, and using a shared code segment.

	Each instance of the module has its own stack and BSS data, but
	shares the static data.

	Therefore, if you intend to keep 'local' data that persists between
	callbacks, you must store it a) on the stack, or b) in unitialized
	data.

	The module's context is switched during every callback (ala windows).

	If you want to share a writable variable between all instances, be sure
	that it is not located within the last paragraph of the static data
	segment, as the BSS area is rounded down to the previous paragraph.

	Therefore up to 15 bytes of static data may not actually be common
	between instances. This amount is called the `Pump Size' and can
	be determined using the Object Information Display of Charon.

	This .h file provides the defines and mechanisms to allow the
	module creator to test the module as a stand-alone program, conversion
	to a module involves recompiling with a #define set.



	Callbacks are achieved by defining a few common functions that
	provide I/O for the module.

	The '_start' procedure must be the first procedure defined
	in the executable file. You may have other procedures, but they
	must be defined after _start.

	the definition for _start is

		int _start(argc, char *argv[], struct NXlate far *callptr)

	where callptr is a far ptr to a data item that must be returned
	in all callbacks.


	The callback.c module includes a definition for _start which
	calls a main(int argc, char *argv[]) function...

	Before including this module, you must #define a setting to
	indicate if the program will be a module, or standalone.

	#define	STANDALONE	0		 compile as module
	#define	STANDALONE	1		compile as standalone program
*/

#define	STDIN	0
#define	STDOUT	1
#define	STDERR	2

#define	CB_READ		0
#define	CB_WRITE	1
#define	CB_GETENV	2
#define	CB_SETENV	3
#define	CB_TELLP	4
#define	CB_SEEKP	5
#define	CB_MAXCALLS	5

/* define valid return codes, OR them together optional returncode in lower byte */
#define	RT_CHANGED_TEXT	0x4000	/* the output file was updated */
#define	RT_CHANGED_TAGS	0x2000	/* the file attribute tags were changed */
#define	RT_FAILED	0x1000	/* I couldn't translate this file */
#define	RT_OK		0x0800	/* I did what I could and I finished ok */


#define	MAX_STRING	256

#ifndef	MASTER_SOURCE

#ifndef	STANDALONE
#error You must define the STANDALONE def
#endif
#if	!defined(__TINY__)
#error You must compile in the tiny model only
#endif
#if	defined(__OVERLAY__)
#error	You must not compile with overlays
#endif

int	read(int handle, char *buffer, int count); /* returns bytes read */
int	write(int handle, char *buffer, int count); /* returns bytes written */

char	*getenv(char *string);

#if	STANDALONE
#define	tellp(handle)	lseek(handle,0L,1)
#define setenv(s)       putenv(s)
#else
void	setenv(char *string);
long	tellp(int handle);
#endif

long	seekp(int handle, long offset, int whence);

int	fprintf(int handle, char *format, ...);

#ifndef	SEEK_CUR
#define SEEK_CUR    1
#define SEEK_END    2
#define SEEK_SET    0
#endif


#endif
#endif