bdos.mac

		TITLE	BDOS - 27 Jan 91 - MT
		SUBTTL	'BDOS and BIOS calls'
;
		INCLUDE	SYMBOLS
;
;-- Implements a tidy means of accessing BDOS and BIOS routines directly. 
;
;   The  base address of the BIOS jump table is easily found as the MSB  of
;   the address specified in the JMP instruction at 0000H.  Making the BIOS
;   function codes the same as the offsets of the jump addresses simplifies
;   the task of finding the address of the BIOS entry point.
;
;-- This program is free software: you can redistribute it and/or modify it
;   under  the terms of the GNU General Public License as published by  the
;   Free Software Foundation, either version 3 of the License, or (at  your
;   option) any later version.
;
;   This  program  is distributed in the hope that it will be  useful,  but
;   WITHOUT   ANY   WARRANTY;  without  even  the   implied   warranty   of
;   MERCHANTABILITY  or  FITNESS  FOR A PARTICULAR  PURPOSE.  See  the  GNU
;   General Public License for more details.
;
;   You should have received a copy of the GNU General Public License along
;   with this program.  If not, see <http://www.gnu.org/licenses/>.
;
;-- Calculate BIOS entry point from BIOS function number. 
;
;   To maintain compatibility with BDOS calls the calling convention is  as
;   follows:
;
;	C  = BIOS Function.		A = Return status or character.
;	E  = Byte arguments.
;	DE = Word argumants.
;
;** 10 Apr 91 -	Modified to use the jump address at CPM$Base + 1 (0001H) to
;		find BIOS offset - MT
;
BIOS::		LD	HL,(CPM$Base + 1)	; Get address of warmstart routine and use hi byte as BIOS address.
		LD	L,C			; Put code (actually the offset into the jump table) in to LSB of address, and the BIOS 
		LD	C,E			; offset into the MSB. Put or word byte arguments into BC where the BIOS expects them.
		LD	B,D
		JP	(HL)			; Jump to BIOS function...
;
BDOS::		JP	0005H
;
		END