;*********************************************************************
;* Title: code-vdgsg4-v00.asm
;*********************************************************************
;* Author: R. Allen Murphey
;*
;* License: Copyright (c) 2020-2022 R. Allen Murphey. All Rights Reserved.
;*
;* Description: Setup CoCo 1/2 VDG SG4 Screen
;*
;* Documentation:
;* VIDRAM: equ $0400 ; START OF SCREEN MEM
;* ENDVID: equ $0600 ; END OF SCREEN MEM
;*
;* Include Files: PIA, SAM
;*
;* Assembler: lwasm 1.4.2
;*
;* Revision History:
;* Rev # Date Who Comments
;* ----- ----------- ------ ---------------------------------------
;* 00 2020-2021 RAM Created
;*********************************************************************
SG4:
ldx $FFFE ; check reset vector
cmpx #$A027 ; CoCo 1/2 reset vector
beq SG4010 ; It's CoCo 1/2, go straight there
lda ACVCINIT0 ; get current ACVC configuration
ora #%10000000 ; force CoCo 1/2 bit 7 on
sta ACVCINIT0 ; get ACVC INIT0 register setup
lda #%00000110 ; configure video mode register
sta ACVCVIDM ; configure 12 lines per row
lda #%00000001 ; -,00=LPF 192,000=HRES32,01=CRES32
sta ACVCVIDR ; Configure LPF,HRES,CRES
ldd #$E080 ; setup memory location for $0400 VIDRAM
std ACVCVOFF1 ; store MSB/LSB to offset register
lda #$0F ; initialize vertical scroll for coco1/2
sta ACVCVSCRL ; store in ACVC vertical scroll register
SG4010: ; Setup for drawing on 32x16x9 alpha/semigraphics 4
pshs A,X,CC ; SAVE MODIFIED REGISTERS ON STACK
lda #1 ; Arbitrary video driver #1
sta VIDDRV ; Save this for use elsewhere for which screen we're on
ldx #$0400 ; We are going to drop .5K screen here
stx VIDRAM ; Our video RAM base address
ldx #$0600 ; The screen is going to be .5K
stx ENDVID ; The ending video address
ldx #SG4 ; Now we start loading pointers to SG4 functions
stx IINIT ; Address of this SG4 label goes in IINIT
ldx #SG4CLR ; Address of SG4 clear screen ...
stx ICLEAR ; Goes in ICLEAR
ldx #SG4DRAWCH ; Address of SG4-specific draw character function ...
stx IDRAWCH ; Goes in IDRAWCH
ldx #SG4SCREEN ; Address of SG4-specific screen paint/refresh ...
stx ISCREEN ; Goes in ISCREEN
lda #%00000000 ; SETUP FOR SG4 ALPHANUMERIC/SEMIGRAPHIC SCREEN IN VDG
sta PIA1BD ; SET VDG MODE IN PIA1 DATA PORT B $FF22
; SET VDG MODE IN SAM %000=AI
sta SAMCV0 ; SAM CLR VDG V0 $FFC0
sta SAMCV1 ; SAM CLR VDG V1 $FFC2
sta SAMCV2 ; SAM CLR VDG V2 $FFC4
; SETUP VDG SCREEN OFFSET %0000010=$0400
sta SAMCF0 ; SAM CLR VDG F0 $FFC6
sta SAMSF1 ; SAM SET VDG F1 $FFC9
sta SAMCF2 ; SAM CLR VDG F2 $FFCA
sta SAMCF3 ; SAM CLR VDG F3 $FFCC
sta SAMCF4 ; SAM CLR VDG F4 $FFCE
sta SAMCF5 ; SAM CLR VDG F5 $FFD0
sta SAMCF6 ; SAM CLR VDG F6 $FFD2
puls A,X,CC,PC ; LOAD AND RESTORE MODIFIED REGISTERS
;*********************************************************************
;* SG4CLR
;*
;* Entry Values
;*
;* Exit Values
;* None
;* Control Register Modifications
;* None
;* Subroutines Called
;* None
;*********************************************************************
SG4CLR:
pshs X,D,CC ; SAVE REGISTERS ON STACK
ldx VIDRAM ; START OF CLEAR SCREEN ROUTINE
ldd #$6060 ; TWO SPACES IN A ROW
CLRSPC:
std ,X++ ; STORE TWO SPACES AT ONCE
cmpx ENDVID ; CHECK END OF SCREEN RAM
bne CLRSPC ; NOPE, KEEP LOOPIN
puls X,D,CC,PC ; LOAD REGISTERS FROM STACK AND RETURN
;*********************************************************************
;* SG4DRAWCH
;* DRAW TEXT TO SG4 - SWITCH CHAR TO UPPERCASE IF NEEDED
;*
;* Entry Values
;* SCRNPTR = OFFSET TO SCREEN MEMORY FOR CHARACTER
;* VIDRAM: equ $0400 ; START OF SCREEN MEM
;* ENDVID: equ $0600 ; END OF SCREEN MEM
;* COUNT: rmb 1 ; COUNT FROM 0 TO 255
;* SX: rmb 1 ; SCREEN X COLUMN TO DRAW ON 0-31
;* SY: rmb 1 ; SCREEN Y ROW TO DRAW ON 0-15
;* ROW: rmb 1 ; CHARACTER BITMAP ROW TO DRAW
;* OFFSET: rmb 2 ; SCREEN RAM OFFSET
;*
;* Exit Values
;* None
;* Control Register Modifications
;* None
;* Subroutines Called
;* None
;*********************************************************************
SG4DRAWCH:
pshs A,B,Y,CC ; SAVE REGISTERS FOR RESTORE AT END OF FUNCTION
pshs B ; SAVE B SPECIALLY SO WE CAN USE THEN RESTORE IT
lda #$20 ; ROWS ARE 32 BYTES WIDE
ldb TY ; GET THE TILE ROW
mul ; MUL A*B (THE ROW)
addb TX ; NOW ADD X OFFSET
addd VIDRAM ; NOW ADD VIDEO OFFSET
std SCRNPTR ; SAVE THE RESULT
tfr D,Y ; LOAD CALCULATED OFFSET INTO Y
puls B ; GET BACK OUR SAVED CHARACTER TO DRAW AND START DRAWING
cmpb #$80 ; IS THIS GRAPHICS?
bpl SG4DRAWCH10 ; YES
cmpb #$20 ; IS THIS LOWERCASE?
bpl SG4DRAWCH10 ; NO
addb #$40 ; YES, UPPERCASE IT
SG4DRAWCH10:
stb ,Y ; AND WRITE IT OUT TO ADDRESS Y
puls A,B,Y,CC,PC ; RESTORE REGISTERS AND RETURN
;*********************************************************************
;* SG4SCREEN
;* DRAW AN SG4 TILE SCREEN TILES 0 TO 511
;*
;* Entry Values
;*
;* Exit Values
;* None
;* Control Register Modifications
;* None
;* Subroutines Called
;* None
;*********************************************************************
; FIXME USES FIXED FOREGROUND/BACKGROUND PALETTE SLOTS ON COCO3
SG4SCREEN:
pshs A,B,X,CC ; SAVE ALL THE REGISTERS WE SMASH
ldd #$040C ; PICK DEFAULT PALETTE SLOTS FOR FORE/BACK
sta CLRFORE ; SETUP DEFAULT FOREGROUN
stb CLRBACK ; SETUP DEFAULT BACKGROUND
clra ; ZERO A TO CLEAR HALF OF D
clrb ; ZERO B TO CLEAR HALF OF D
std COUNTER ; ZERO OUT OUR COUNTER FOR 0-511 TILES DRAWN
std SCRNPTR ; ZERO OUT OUR SCREEN MEMORY POINTER
sta ROW ; ZERO OUT THE ROW COUNTER
sta TX ; ZERO OUT THE TILE X
sta TY ; ZERO OUT THE TILE Y
tfr D,X ; ZERO OUT OUR INDEX TOO
SG4ALOOP:
ldb [MAPPTR] ; LOAD THE CHARACTER TO DRAW FROM TILE MAP
jsr SG4DRAWCH ; DRAW IT
inc TX ; MOVE RIGHT ONE TILE
lda TX ; GET NEW TILE COLUMN
cmpa #$20 ; ARE WE AT THE END OF A ROW OF TILES?
bne SG4BLOOP ; NO, KEEP GOING
clr TX ; YES, CLEAR X POSITION TO START OF LINE
lda TY ; GET CURRENT ROW
;adda #12 ; ADD A TILE HEIGHT
adda #1 ; ADD A ROW
sta TY ; SAVE AS NEW ROW
SG4BLOOP:
ldd MAPPTR ; MOVE CHARACTER CURSOR POSITION ...
addd #$01 ; TO NEXT CHARACTER TILE TO DRAW AND ...
std MAPPTR ; SAVE IT
ldd COUNTER ; MOVE SCREEN COUNTER POSITION ...
addd #$01 ; TO NEXT SCREEN LOCATION TO DRAW AND ...
std COUNTER ; SAVE IT
ldd COUNTER ; CHECK TO SEE IF SCREEN COUNTER ...
cmpd #512 ; IS AT THE END OF THE SCREEN
bne SG4ALOOP ; NOPE, GO BACK AND DRAW MORE
puls A,B,X,CC,PC ; YEP, CLEAN UP REGISTERS AND RETURN
;*********************************************************************
;* End of code-vdgsg4-v00.asm
;*********************************************************************