hisiocode-vbi.src

;  highsiocode-vbi.src - highspeed SIO routine, optional fast VBI code
;
;  Copyright (c) 2003-2023 by Matthias Reichl <hias@horus.com>
;
;  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 2 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, write to the Free Software
;  Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.


.if .def FASTVBI

VBICODE 
.if .not .def FASTVBI_NOCLOCK
	INC RTCLOK+2
	BNE ?NOC1
	INC RTCLOK+1

; note: RTCLOK is handeled in hisiocode-main by checking RTCLOK+1 wrap-around
; this saves 7 cycles in worst case
;	BNE ?NOC1
;	INC 18

?NOC1
.endif

; fast implementation of system timer 1:
; - jumps to ?ERRTO if it reaches 0
; - no check if timer has already expired (just set MYTIM1+1 to $FF
;   and it will run long enough before starting the timeout code)
; - MYTIM1+1 has to be set to HIVAL+1, since timer starts at $0000 (not $FFFF).

	DEC MYTIM1
	BNE ?NOTOUT
	DEC MYTIM1+1

	BEQ ?RUNTIM	; timer reached 0, start timeout code

?NOTOUT

; ensure the critical VBICODE doesn't cross a page boundary
.if [ * & $FF00 ] <> [ VBICODE & $FF00 ]
.if .def ALLOW_PAGE_CROSSING
        .warn "VBICODE crosses a page boundary!"
.else
        .error "VBICODE crosses a page boundary! Set ALLOW_PAGE_CROSSING to make this a warning"
.endif
.endif

; note: to save 6 additional cycles we don't use "JMP XITVBV" here
; but implement the OS code directly. This code is identical in all
; OS versions I know of.

	PLA
	TAY
	PLA
	TAX
	PLA
	RTI

; jump to timeout code
?RUNTIM
?ABSF07	JMP ?ERRTO

.if .def RELOCTABLE
?VBIADR
?ABSF08 .WORD VBICODE
.endif

.endif