/*
   This Code was written by Digital Solutions and is hereby placed in the 
   Public Domain under GNU Public License, (Please see attached Copy)
   I, <edmund@bangor.ac.uk>, have agreed to co-ordinate the changes made to
   mxsub and pass them back to Digital Solutions and others
*/
#define	MAX_DRIVES	10
#define	TRUE	1
#define	FALSE	0

int show_regs();
static unsigned _rax, _rbx, _rcx, _rdx, _res;
static unsigned char drive_nos[ MAX_DRIVES];
static char drives = 0;

main( argc, argv)		/* chain into specified vector & exit */
int argc;
char *argv[];
{
	char *p, c, flag, x;
	/* Scan & parse drive list */
	printf( "DIGITAL SOLUTIONS PTY. LTD. MSCDX emulater functions 0 and 0dHex\n");
	if( argc < 2)
	{
		printf( "Usage - MXSUB drive_letter drive_letter ...\n");
		exit(1);
	}
	if( argc > MAX_DRIVES+1)
	{
		printf( "Maximum of %d drives supported\n", MAX_DRIVES);
		exit(2);
	}
	--argc;
	for( drives = 0; drives < MAX_DRIVES && drives < argc; ++drives)
	{
		p = argv[ drives+1];
		c = *p;
		if( !isalpha( c))
		{
			printf( "Argument No. %d (%c) not a vaild drive\n", drives+1,c);
			exit(3);
		}
		drive_nos[ drives] = toupper( c) - 'A';
	}
	/* Have all drives, now sort into ascending order - bsort */
	do
	{
		flag = FALSE;
		for( x = 0; x < drives-1; ++x)
		{
			if( drive_nos[x] > drive_nos[x+1]) /* Need swap */
			{
				c = drive_nos[x+1];
				drive_nos[x+1] = drive_nos[x];
				drive_nos[x] = c;
				flag = TRUE;
			}
		}
	} while( flag);
	printf( "Installed for drives");
	for( x = 0; x < drives; ++x)
	{
		printf( " %c:", drive_nos[x] + 'A');
	}
	printf( "\n");
#asm
	jmp		arnd		;jump around vector save
save_ds	dw	0
chain_vec	dw	0,0
arnd:
	mov		word ptr cs:save_ds,ds	;save data segment for interrupt handlers
	mov		word ptr cs:save_ds,ds	;save data segment for interrupt handlers
	mov		bx,02fh*4	;point to interrupt vector
	mov		ax,0
	mov		es,ax

;vector ->chain_vec

	mov		ax,es:[bx]
	mov		word ptr cs:chain_vec,ax
	mov		ax,es:2[bx]
	mov		word ptr cs:chain_vec+2,ax
#endasm
	;
	install_vector(0x2f, show_regs);
	;
#asm
	mov	ax,3100h	;exit but stay resident code
	mov	dx,120h		;paragraphs to save including code
	int	21h			;ask dos to do it
#endasm
	;
}

show_regs()
{
	char *p, x;
#asm
;	mov	sp,bp
;	pop	bp
;	jmp	far ptr cs:[chain_vec]			;& continue to bios

	push	ds
	push	es
	push	ax
	push	bx
	push	cx
	push	dx
	mov	ds,cs:save_ds			;establish envoirenment

;	move register contents to where we can get them

	mov	word ptr _rax_,ax
	mov	word ptr _rbx_,bx
	mov	word ptr _rcx_,cx
	mov	word ptr _rdx_,dx
	mov	word ptr _res_,es
#endasm
	if( (_rax & 0xff00) == 0x1500)
	{
	;
#asm
	pop	dx
	pop	cx
	pop	bx
	pop	ax
	pop	es
#endasm
	;
		switch( _rax & 0xff)
		{
			case 0:	/* Func 0 */
				_rbx = drives;			/* # of drives */
				_rcx = drive_nos[0];	/* First drive  */
				break;
			case 0x0d:
					/* func 13 */
				p = (char *)((((long) _res) << 16) | _rbx); /* o/p buffer ptr */
				for( x = 0; x < drives; ++x)
				{
					*p++ = drive_nos[x];
				}
				break;
			default:
				;
#asm
	mov	ax,3		;set video mode 3
	int	10h
#endasm
				;
				printf( "MXSUB error - unsupported function %02x (Hex)",
					_rax & 0xff);
/*
				printf( "\nax:%04x bx:%04x cx:%04x dx:%04x es:%04x\n",
					_rax,_rbx,_rcx,_rdx,_res);
*/
				ki();
				break;
		}
	;
#asm
	mov	 ax,word ptr _rax_
	mov	 bx,word ptr _rbx_
	mov	 cx,word ptr _rcx_
	mov	 dx,word ptr _rdx_
	mov	 es,word ptr _res_
	pop	ds
	mov	sp,bp
	pop	bp
	iret
#endasm
	;
	}
	;
#asm
	pop	dx
	pop	cx
	pop	bx
	pop	ax
	pop	es
	pop	ds
	mov	sp,bp
	pop	bp
	jmp	far ptr cs:[chain_vec]			;& continue to bios
#endasm
}

putchar( c)
char c;
{
	if( c == '\n') putchar( '\r');
	;
#asm
	mov	ah,14
	mov	al,[6+bp]
	mov	bx,7
	mov	cx,1
	int	10h
#endasm
	;
}

ki()
{
#asm
	mov	ah,0		;get char from keyboard func
	int	16h			;call bios
#endasm
}


install_vector( vector_no, new_vector)
char vector_no;
int (*new_vector)();
{
	int (**vptr)();		/* pointer to vector */
	vptr = (long)vector_no << 2;
	;
#asm
	cli				;interrupts off
#endasm
	*vptr = new_vector;		/* install new vector */
	;
#asm
	sti
#endasm
}

isalpha( c)
char c;
{
	return (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z');
}

toupper( c)
char c;
{
	if( c >= 'a' && c <= 'z') return (c-'a') + 'A';
	return c;
}