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macro.h
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; MACRO.H
; Version 1.06, 3/SEPTEMBER/2004
VERSION_MACRO = 106
;
; THIS FILE IS EXPLICITLY SUPPORTED AS A DASM-PREFERRED COMPANION FILE
; PLEASE DO *NOT* REDISTRIBUTE MODIFIED VERSIONS OF THIS FILE!
;
; This file defines DASM macros useful for development for the Atari 2600.
; It is distributed as a companion machine-specific support package
; for the DASM compiler. Updates to this file, DASM, and associated tools are
; available at at http://www.atari2600.org/dasm
;
; Many thanks to the people who have contributed. If you take issue with the
; contents, or would like to add something, please write to me
; (atari2600@taswegian.com) with your contribution.
;
; Latest Revisions...
;
; 1.06 03/SEP/2004 - nice revision of VERTICAL_BLANK (Edwin Blink)
; 1.05 14/NOV/2003 - Added VERSION_MACRO equate (which will reflect 100x version #)
; This will allow conditional code to verify MACRO.H being
; used for code assembly.
; 1.04 13/NOV/2003 - SET_POINTER macro added (16-bit address load)
;
; 1.03 23/JUN/2003 - CLEAN_START macro added - clears TIA, RAM, registers
;
; 1.02 14/JUN/2003 - VERTICAL_SYNC macro added
; (standardised macro for vertical synch code)
; 1.01 22/MAR/2003 - SLEEP macro added.
; - NO_ILLEGAL_OPCODES switch implemented
; 1.0 22/MAR/2003 Initial release
; Note: These macros use illegal opcodes. To disable illegal opcode usage,
; define the symbol NO_ILLEGAL_OPCODES (-DNO_ILLEGAL_OPCODES=1 on command-line).
; If you do not allow illegal opcode usage, you must include this file
; *after* including VCS.H (as the non-illegal opcodes access hardware
; registers and require them to be defined first).
; Available macros...
; SLEEP n - sleep for n cycles
; VERTICAL_SYNC - correct 3 scanline vertical synch code
; CLEAN_START - set machine to known state on startup
; SET_POINTER - load a 16-bit absolute to a 16-bit variable
;-------------------------------------------------------------------------------
; SLEEP duration
; Original author: Thomas Jentzsch
; Inserts code which takes the specified number of cycles to execute. This is
; useful for code where precise timing is required.
; ILLEGAL-OPCODE VERSION DOES NOT AFFECT FLAGS OR REGISTERS.
; LEGAL OPCODE VERSION MAY AFFECT FLAGS
; Uses illegal opcode (DASM 2.20.01 onwards).
MAC SLEEP ;usage: SLEEP n (n>1)
.CYCLES SET {1}
IF .CYCLES < 2
ECHO "MACRO ERROR: 'SLEEP': Duration must be > 1"
ERR
ENDIF
IF .CYCLES & 1
IFNCONST NO_ILLEGAL_OPCODES
nop 0
ELSE
bit VSYNC
ENDIF
.CYCLES SET .CYCLES - 3
ENDIF
REPEAT .CYCLES / 2
nop
REPEND
ENDM
;-------------------------------------------------------------------------------
; VERTICAL_SYNC
; revised version by Edwin Blink -- saves bytes!
; Inserts the code required for a proper 3 scanline vertical sync sequence
; Note: Alters the accumulator
; OUT: A = 0
MAC VERTICAL_SYNC
lda #%1110 ; each '1' bits generate a VSYNC ON line (bits 1..3)
.VSLP1 sta WSYNC ; 1st '0' bit resets Vsync, 2nd '0' bit exit loop
sta VSYNC
lsr
bne .VSLP1 ; branch until VYSNC has been reset
ENDM
;-------------------------------------------------------------------------------
; CLEAN_START
; Original author: Andrew Davie
; Standardised start-up code, clears stack, all TIA registers and RAM to 0
; Sets stack pointer to $FF, and all registers to 0
; Sets decimal mode off, sets interrupt flag (kind of un-necessary)
; Use as very first section of code on boot (ie: at reset)
; Code written to minimise total ROM usage - uses weird 6502 knowledge :)
MAC CLEAN_START
sei
cld
ldx #0
txa
tay
.CLEAR_STACK dex
txs
pha
bne .CLEAR_STACK ; SP=$FF, X = A = Y = 0
ENDM
;-------------------------------------------------------
; SET_POINTER
; Original author: Manuel Rotschkar
;
; Sets a 2 byte RAM pointer to an absolute address.
;
; Usage: SET_POINTER pointer, address
; Example: SET_POINTER SpritePTR, SpriteData
;
; Note: Alters the accumulator, NZ flags
; IN 1: 2 byte RAM location reserved for pointer
; IN 2: absolute address
MAC SET_POINTER
.POINTER SET {1}
.ADDRESS SET {2}
LDA #<.ADDRESS ; Get Lowbyte of Address
STA .POINTER ; Store in pointer
LDA #>.ADDRESS ; Get Hibyte of Address
STA .POINTER+1 ; Store in pointer+1
ENDM
;-------------------------------------------------------
; BOUNDARY byte#
; Original author: Denis Debro (borrowed from Bob Smith / Thomas)
;
; Push data to a certain position inside a page and keep count of how
; many free bytes the programmer will have.
;
; eg: BOUNDARY 5 ; position at byte #5 in page
.FREE_BYTES SET 0
MAC BOUNDARY
REPEAT 256
IF <. % {1} = 0
MEXIT
ELSE
.FREE_BYTES SET .FREE_BYTES + 1
.byte $00
ENDIF
REPEND
ENDM
;-------------------------------------------------------
; SKIP_SCANLINES #lines
;
; Skip a given # of scanlines.
; Sets the X register to zero.
MAC SKIP_SCANLINES
.LINES SET {1}
ldx #.LINES
.vblank sta WSYNC
dex
bne .vblank
ENDM
; EOF