;======================================================================
;	VGA DRIVER FOR RBC PROJECT
;
;	WRITTEN BY: WAYNE WARTHEN -- 5/29/2017
;======================================================================
;
; TODO:
;
;======================================================================
; VGA DRIVER - CONSTANTS
;======================================================================
;
VGA_BASE	.EQU	$E0
;
VGA_KBDDATA	.EQU	VGA_BASE + $00	; KBD CTLR DATA PORT
VGA_KBDST	.EQU	VGA_BASE + $01	; KBD CTLR STATUS/CMD PORT
VGA_REG		.EQU	VGA_BASE + $02	; SELECT CRTC REGISTER
VGA_DATA	.EQU	VGA_BASE + $03	; READ/WRITE CRTC DATA
VGA_CFG		.EQU	VGA_BASE + $04	; VGA3 BOARD CFG REGISTER
VGA_HI		.EQU	VGA_BASE + $05	; BOARD RAM HI ADDRESS
VGA_LO		.EQU	VGA_BASE + $06	; BOARD RAM LO ADDRESS
VGA_DAT		.EQU	VGA_BASE + $07	; BOARD RAM BYTE R/W
;
VGA_ROWS	.EQU	25
VGA_COLS	.EQU	80
;
#DEFINE		DEFREGS		REGS_VGA
;
TERMENABLE	.SET	TRUE		; INCLUDE TERMINAL PSEUDODEVICE DRIVER
;
;======================================================================
; VGA DRIVER - INITIALIZATION
;======================================================================
;
VGA_INIT:
	LD	IY,VGA_IDAT		; POINTER TO INSTANCE DATA
;
	CALL	NEWLINE			; FORMATTING
	PRTS("VGA: IO=0x$")
	LD	A,VGA_REG
	CALL	PRTHEXBYTE
	CALL	VGA_PROBE		; CHECK FOR HW PRESENCE
	JR	Z,VGA_INIT1		; CONTINUE IF HW PRESENT
;
	; HARDWARE NOT PRESENT
	PRTS(" NOT PRESENT$")
	OR	$FF			; SIGNAL FAILURE
	RET
;
VGA_INIT1:
	; DISPLAY CONSOLE DIMENSIONS
	LD	A,VGA_COLS
	CALL	PC_SPACE
	CALL	PRTDECB
	LD	A,'X'
	CALL	COUT
	LD	A,VGA_ROWS
	CALL	PRTDECB
	PRTS(" TEXT$")

	; HARDWARE INITIALIZATION
	CALL 	VGA_CRTINIT		; SETUP THE VGA CHIP REGISTERS
	CALL	VGA_LOADFONT		; LOAD FONT DATA FROM ROM TO VGA STRORAGE
	CALL	VGA_VDARES
	CALL	KBD_INIT		; INITIALIZE KEYBOARD DRIVER
	
	; ADD OURSELVES TO VDA DISPATCH TABLE
	LD	BC,VGA_DISPATCH		; BC := DISPATCH ADDRESS
	LD	DE,VGA_IDAT		; DE := VGA INSTANCE DATA PTR
	CALL	VDA_ADDENT		; ADD ENTRY, A := UNIT ASSIGNED

	; INITIALIZE EMULATION
	LD	C,A			; C := ASSIGNED VIDEO DEVICE NUM
	LD	DE,VGA_DISPATCH		; DE := DISPATCH ADDRESS
	LD	HL,VGA_IDAT		; HL := VGA INSTANCE DATA PTR
	CALL	TERM_ATTACH		; DO IT

	XOR	A			; SIGNAL SUCCESS
	RET
;
;======================================================================
; VGA DRIVER - VIDEO DISPLAY ADAPTER (VDA) DISPATCHER AND FUNCTIONS
;======================================================================
;
VGA_DISPATCH:
	LD	A,B		; GET REQUESTED FUNCTION
	AND	$0F		; ISOLATE SUB-FUNCTION

	JP	Z,VGA_VDAINI	; $40
	DEC	A
	JP	Z,VGA_VDAQRY	; $41
	DEC	A
	JP	Z,VGA_VDARES	; $42
	DEC	A
	JP	Z,VGA_VDADEV	; $43
	DEC	A
	JP	Z,VGA_VDASCS	; $44
	DEC	A
	JP	Z,VGA_VDASCP	; $45
	DEC	A
	JP	Z,VGA_VDASAT	; $46
	DEC	A
	JP	Z,VGA_VDASCO	; $47
	DEC	A
	JP	Z,VGA_VDAWRC	; $48
	DEC	A
	JP	Z,VGA_VDAFIL	; $49
	DEC	A
	JP	Z,VGA_VDACPY	; $4A
	DEC	A
	JP	Z,VGA_VDASCR	; $4B
	DEC	A
	JP	Z,KBD_STAT	; $4C
	DEC	A
	JP	Z,KBD_FLUSH	; $4D
	DEC	A
	JP	Z,KBD_READ	; $4E
	CALL	PANIC

VGA_VDAINI:
	; RESET VDA
	; CURRENTLY IGNORES VIDEO MODE AND BITMAP DATA
	CALL	VGA_VDARES	; RESET VDA
	XOR	A		; SIGNAL SUCCESS
	RET

VGA_VDAQRY:
	LD	C,$00		; MODE ZERO IS ALL WE KNOW
	LD	D,VGA_ROWS	; ROWS
	LD	E,VGA_COLS	; COLS
	LD	HL,0		; EXTRACTION OF CURRENT BITMAP DATA NOT SUPPORTED YET
	XOR	A		; SIGNAL SUCCESS
	RET
	
VGA_VDARES:
	LD	A,$07		; ATTRIBUTE IS STANDARD WHITE ON BLACK
	LD	(VGA_ATTR),A	; SAVE IT
	XOR	A		; ZERO (REVEVERSE, UNDERLINE, BLINK)
	LD	(VGA_RUB),A	; SAVE IT
	
	LD	DE,0		; ROW = 0, COL = 0
	CALL	VGA_XY		; SEND CURSOR TO TOP LEFT
	LD	A,' '		; BLANK THE SCREEN
	LD	DE,$800		; FILL ENTIRE BUFFER
	CALL	VGA_FILL	; DO IT
	LD	DE,0		; ROW = 0, COL = 0
	CALL	VGA_XY		; SEND CURSOR TO TOP LEFT
	
	LD	HL,$0404	; SET VIDEO ENABLE BIT
	CALL	VGA_SETCFG	; DO IT
	
	XOR	A
	RET

VGA_VDADEV:
	LD	D,VDADEV_VGA	; D := DEVICE TYPE
	LD	E,0		; E := PHYSICAL UNIT IS ALWAYS ZERO
	XOR	A		; SIGNAL SUCCESS
	RET
	
VGA_VDASCS:
	CALL	PANIC		; NOT IMPLEMENTED (YET)
	
VGA_VDASCP:
	CALL	VGA_XY		; SET CURSOR POSITION
	XOR	A		; SIGNAL SUCCESS
	RET
	
VGA_VDASAT:
	; INCOMING IS:  -----RUB (R=REVERSE, U=UNDERLINE, B=BLINK)
	;
	; JUST SAVE THE VALUE AND FALL THROUGH.  ONLY REVERSE IS
	; SUPPORTED WHICH IS IMPLEMENTED BELOW.
	LD	A,E
	LD	(VGA_RUB),A	; SAVE IT
	JR	VGA_VDASCO2	; IMPLEMENT SETTING
	
VGA_VDASCO:
	; INCOMING IS:  IBGRIBGR (I=INTENSITY, B=BLUE, G=GREEN, R=RED)
	; TRANSFORM TO: -RGBIRGB (DISCARD INTENSITY BIT IN HIGH NIBBLE)
	;
	; A := INVERTED E, SO A IS RGBIRGBI (F/B)
	LD	B,8		; DO 8 BITS
VGA_VDASCO1:
	RRC	E		; LOW BIT OF E ROTATED RIGHT INTO CF
	RLA			; CF ROTATED LEFT INTO LOW BIT OF A
	DJNZ	VGA_VDASCO1	; DO FOR ALL 8 BITS
	; LS A X 3 TO SWAP F/B BITS, SO A IS IRGBIRGB (B/F)
	RLCA
	RLCA
	RLCA
	; MASK FOR RELEVANT BITS, SO A IS 0R0B0R0B
	AND	%01010101
	; SAVE A IN C AND SET A = E
	LD	C,A
	LD	A,E
	; MASK FOR RELEVANT BITS, SO A IS 00G0I0G0
	AND	%00101010
	; COMBINE WITH SAVED
	OR	E
	; SAVE NEW ATTR VALUE
	LD	(VGA_ATTR),A	; AND SAVE THE RESULT
VGA_VDASCO2:
	; CHECK FOR REVERSE VIDEO
	LD	A,(VGA_RUB)	; GET RUB SETTING
	BIT	2,A		; REVERSE IS BIT 2
	JR	Z,VGA_VDASCO3	; DONE IF REVERSE VID NOT SET
	; IMPLEMENT REVERSE VIDEO
	LD	A,(VGA_ATTR)	; GET ATTRIBUTE
	PUSH	AF		; SAVE IT
	AND	%00001000	; ISOLATE INTENSITY BIT
	LD	E,A		; SAVE IN E
	POP	AF		; GOT ATTR BACK
	RLCA			; SWAP FG/BG COLORS
	RLCA
	RLCA
	RLCA
	AND	%01110111	; REMOVE HIGH BITS
	OR	E		; COMBINE WITH PREVIOUS INTENSITY BIT
	LD	(VGA_ATTR),A	; SAVE NEW VALUE
VGA_VDASCO3:
	XOR	A		; SIGNAL SUCCESS
	RET
	
VGA_VDAWRC:
	LD	A,E		; CHARACTER TO WRITE GOES IN A
	CALL	VGA_PUTCHAR	; PUT IT ON THE SCREEN
	XOR	A		; SIGNAL SUCCESS
	RET
	
VGA_VDAFIL:
	LD	A,E		; FILL CHARACTER GOES IN A
	EX	DE,HL		; FILL LENGTH GOES IN DE
	CALL	VGA_FILL	; DO THE FILL
	XOR	A		; SIGNAL SUCCESS
	RET

VGA_VDACPY:
	; LENGTH IN HL, SOURCE ROW/COL IN DE, DEST IS VGA_POS
	; BLKCPY USES: HL=SOURCE, DE=DEST, BC=COUNT
	PUSH	HL		; SAVE LENGTH
	CALL	VGA_XY2IDX	; ROW/COL IN DE -> SOURCE ADR IN HL
	POP	BC		; RECOVER LENGTH IN BC
	LD	DE,(VGA_POS)	; PUT DEST IN DE
	JP	VGA_BLKCPY	; DO A BLOCK COPY
	
VGA_VDASCR:
	LD	A,E		; LOAD E INTO A
	OR	A		; SET FLAGS
	RET	Z		; IF ZERO, WE ARE DONE
	PUSH	DE		; SAVE E
	JP	M,VGA_VDASCR1	; E IS NEGATIVE, REVERSE SCROLL
	CALL	VGA_SCROLL	; SCROLL FORWARD ONE LINE
	POP	DE		; RECOVER E
	DEC	E		; DECREMENT IT
	JR	VGA_VDASCR	; LOOP
VGA_VDASCR1:
	CALL	VGA_RSCROLL	; SCROLL REVERSE ONE LINE
	POP	DE		; RECOVER E
	INC	E		; INCREMENT IT
	JR	VGA_VDASCR	; LOOP
;
;======================================================================
; VGA DRIVER - PRIVATE DRIVER FUNCTIONS
;======================================================================
;
;----------------------------------------------------------------------
; SET BOARD CONFIGURATON REGISTER
;   MASK IN H, VALUE IN L
;----------------------------------------------------------------------
;
VGA_SETCFG:
	PUSH	AF		; PRESERVE AF
	LD	A,H		; MASK IN ACCUM
	CPL			; INVERT IT
	LD	H,A		; BACK TO H
	LD	A,(VGA_CFGV)	; GET CURRENT CONFIG VALUE
	AND	H		; RESET ALL TARGET BITS
	OR	L		; SET TARGET BITS
	LD	(VGA_CFGV),A	; SAVE NEW VALUE
	OUT	(VGA_CFG),A	; AND WRITE IT TO REGISTER
	POP	AF		; RESTORE AF
	RET
;
;----------------------------------------------------------------------
; UPDATE CRTC REGISTERS
;   VGA_REGWR WRITES VALUE IN A TO VDU REGISTER SPECIFIED IN C
;----------------------------------------------------------------------
;
VGA_REGWR:
	PUSH	AF			; SAVE VALUE TO WRITE
	LD	A,C			; SET A TO VGA REGISTER TO SELECT
	OUT	(VGA_REG),A		; WRITE IT TO SELECT THE REGISTER
	POP	AF			; RESTORE VALUE TO WRITE
	OUT	(VGA_DATA),A		; WRITE IT
	RET
;
VGA_REGWRX:
	LD	A,H			; SETUP MSB TO WRITE
	CALL	VGA_REGWR		; DO IT
	INC	C			; NEXT CVDU REGISTER
	LD	A,L			; SETUP LSB TO WRITE
	JR	VGA_REGWR		; DO IT & RETURN
;
;----------------------------------------------------------------------
; READ CRTC REGISTERS
;   VGA_REGRD READS VDU REGISTER SPECIFIED IN C AND RETURNS VALUE IN A
;----------------------------------------------------------------------
;
VGA_REGRD:
	LD	A,C			; SET A TO VGA REGISTER TO SELECT
	OUT	(VGA_REG),A		; WRITE IT TO SELECT THE REGISTER
	IN	A,(VGA_DATA)		; READ IT
	RET
;
VGA_REGRDX:
	CALL	VGA_REGRD		; GET VALUE FROM REGISTER IN C
	LD	H,A			; SAVE IN H
	INC	C			; BUMP TO NEXT REGISTER OF PAIR
	CALL	VGA_REGRD		; READ THE VALUE
	LD	L,A			; SAVE IT IN L
	RET
;
;----------------------------------------------------------------------
; WRITE VIDEO RAM
;   VGA_MEMWR WRITES VALUE IN A TO ADDRESS IN DE
;   VGA_MEMWRX WRITES VALUE IN HL TO ADDRESS IN DE
;----------------------------------------------------------------------
;
VGA_MEMWR:
	LD	C,VGA_HI
	OUT	(C),D
	INC	C
	OUT	(C),E
	INC	C
	OUT	(C),A
	RET
;
VGA_MEMWRX:
	LD	C,VGA_HI
	OUT	(C),D
	INC	C
	OUT	(C),E
	INC	C
	OUT	(C),H
	INC	E
	DEC	C
	OUT	(C),E
	INC	C
	OUT	(C),L
	DEC	E
	RET
;
;----------------------------------------------------------------------
; READ VIDEO RAM
;   VGA_MEMRD READS VALUE IN DE TO A
;   VGA_MEMRDX READS VALUE IN DE TO HL
;----------------------------------------------------------------------
;
VGA_MEMRD:
	LD	C,VGA_HI
	OUT	(C),D
	INC	C
	OUT	(C),E
	INC	C
	IN	A,(C)
	RET
;
VGA_MEMRDX:
	LD	C,VGA_HI
	OUT	(C),D
	INC	C
	OUT	(C),E
	INC	C
	IN	H,(C)
	INC	E
	DEC	C
	OUT	(C),E
	INC	C
	IN	L,(C)
	DEC	E
	RET
;
;----------------------------------------------------------------------
; PROBE FOR VGA HARDWARE
;----------------------------------------------------------------------
;
; ON RETURN, ZF SET INDICATES HARDWARE FOUND
;
VGA_PROBE:
	LD	DE,0			; POINT TO FIRST BYTE OF VRAM
	LD	A,$A5			; INITIAL TEST VALUE
	LD	B,A			; SAVE IN B
	CALL	VGA_MEMWR		; WRITE IT
	INC	E			; NEXT BYTE OF VRAM
	CPL				; INVERT TEST VALUE
	CALL	VGA_MEMWR		; WRITE IT
	DEC	E			; BACK TO FIRST BYTE OF VRAM
	CALL	VGA_MEMRD		; READ IT
	CP	B			; CHECK FOR TEST VALUE
	RET	NZ			; RETURN NZ IF FAILURE
	INC	E			; SECOND VRAM BYTE
	CALL	VGA_MEMRD		; READ IT
	CPL				; INVERT IT
	CP	B			; CHECK FOR INVERTED TEST VALUE
	RET				; RETURN WITH ZF SET BASED ON CP
;
;----------------------------------------------------------------------
; CRTC DISPLAY CONTROLLER CHIP INITIALIZATION
;----------------------------------------------------------------------
;
VGA_CRTINIT:
	LD	HL,$FF00		; ZERO ALL CFG BITS
	CALL	VGA_SETCFG		; DO IT

	CALL	VGA_RES			; RESET CRTC (ALL REGS TO ZERO)

	LD	HL,DEFREGS		; HL = POINTER TO TABLE OF REG VALUES
VGA_CRTINIT1:
	LD	A,(HL)			; FIRST BYTE IS REG ADR
	LD	C,A			; PUT IN C FOR LATER
	INC	A			; TEST FOR END MARKER ($FF)
	RET	Z			; IF EQUAL, DONE
	INC	HL			; NEXT BYTE
	LD	A,(HL)			; SECOND BYTE IS REG VAL
	INC	HL			; HL TO NEXT ENTRY
	CALL	VGA_REGWR		; WRITE REGISTER VALUE
	JR	VGA_CRTINIT1		; LOOP
;
VGA_RES:
	LD	C,0			; START WITH REG ZERO
	LD	B,40			; CLEAR 40 REGISTERS
VGA_RES1:
	XOR	A			; VALUE IS ZERO
	CALL	VGA_REGWR		; SET VALUE
	INC	C			; NEXT REGISTER
	DJNZ	VGA_RES1		; LOOP TILL DONE
	RET				; DONE
;
VGA_CRTCDUMP:
	LD	C,0			; START WITH REG ZERO
	LD	B,40			; CLEAR 40 REGISTERS
VGA_CRTCDUMP1:
	CALL	VGA_REGRD		; SET VALUE
	CALL	PRTHEXBYTE
	CALL	PC_SPACE
	INC	C			; NEXT REGISTER
	DJNZ	VGA_CRTCDUMP1		; LOOP TILL DONE
	RET				; DONE
;
;----------------------------------------------------------------------
; LOAD FONT DATA
;----------------------------------------------------------------------
;
VGA_LOADFONT:
	LD	HL,$7000		; CLEAR FONT PAGE NUM
	CALL	VGA_SETCFG

	LD	DE,$7000		; PAGE 7 OF VIDEO RAM
	LD	HL,FONT_HI		; START OF FONT DATA
VGA_LOADFONT1:
	LD	A,(HL)			; GET NEXT BYTE
	CALL	VGA_MEMWR		; MEM(DE) := A
	INC	HL			; NEXT FONT BYTE
	INC	DE			; NEXT MEM BYTE
	LD	A,D
	CP	$80			; CHECK FOR END
	JR	NZ,VGA_LOADFONT1	; LOOP
	LD	HL,$7070		; SET FONT PAGE NUM TO 7
	CALL	VGA_SETCFG
	RET				; DONE
;
;----------------------------------------------------------------------
; SET CURSOR POSITION TO ROW IN D AND COLUMN IN E
;----------------------------------------------------------------------
;
VGA_XY:
	CALL	VGA_XY2IDX		; CONVERT ROW/COL TO BUF IDX
	LD	(VGA_POS),HL		; SAVE THE RESULT (DISPLAY POSITION)
    	LD 	C,14			; CURSOR POSITION REGISTER PAIR
	JP	VGA_REGWRX		; DO IT AND RETURN
;
;----------------------------------------------------------------------
; CONVERT XY COORDINATES IN DE INTO LINEAR INDEX IN HL
; D=ROW, E=COL
;----------------------------------------------------------------------
;
VGA_XY2IDX:
	LD	A,E			; SAVE COLUMN NUMBER IN A
	LD	H,D			; SET H TO ROW NUMBER
	LD	E,VGA_COLS		; SET E TO ROW LENGTH
	CALL	MULT8			; MULTIPLY TO GET ROW OFFSET
	LD	E,A			; GET COLUMN BACK
	ADD	HL,DE			; ADD IT IN
	RET				; RETURN
;
;----------------------------------------------------------------------
; WRITE VALUE IN A TO CURRENT VDU BUFFER POSTION, ADVANCE CURSOR
;----------------------------------------------------------------------
;
VGA_PUTCHAR:
	; SETUP DE WITH BUFFER ADDRESS
	LD	DE,(VGA_POS)		; GET CURRENT POSITION
	RL	E			; MULTIPLY BY 2
	RL	D			; ... 2 BYTES PER CHAR
	; SETUP CHAR/ATTR IN HL
	LD	H,A			; CHARACTER
	LD	A,(VGA_ATTR)		; ATTRIBUTE
	LD	L,A			; ... TO L
	; WRITE CHAR & ATTR
	CALL	VGA_MEMWRX
	; UPDATE CURRENT POSITION
	LD	HL,(VGA_POS)		; GET CURSOR POSITION
	INC	HL			; INCREMENT
	LD	(VGA_POS),HL		; SAVE NEW POSITION
    	LD 	C,14			; CURSOR POSITION REGISTER PAIR
	JP	VGA_REGWRX		; DO IT AND RETURN
;
;----------------------------------------------------------------------
; FILL AREA IN BUFFER WITH SPECIFIED CHARACTER AND CURRENT COLOR/ATTRIBUTE
; STARTING AT THE CURRENT FRAME BUFFER POSITION
;   A: FILL CHARACTER
;   DE: NUMBER OF CHARACTERS TO FILL
;----------------------------------------------------------------------
;
VGA_FILL:
	PUSH	DE			; COUNT ON STACK
	LD	H,A			; H = CHAR
	LD	A,(VGA_ATTR)		; GET CUR ATTR
	LD	L,A			; PUT INT L

	; SETUP DE WITH INITIAL BUFFER ADDRESS
	LD	DE,(VGA_POS)		; GET CURRENT POSITION
	RL	E			; MULTIPLY BY 2
	RL	D			; ... 2 BYTES PER CHAR
	LD	C,VGA_HI

VGA_FILL1:
	OUT	(C),D			; SET HI ADDR
	INC	C			; POINT TO LO ADDR REG

VGA_FILL2:
	EX	(SP),HL			; HL = COUNT, SAVE CHAR/ATTR
	LD	A,H			; CHECK FOR
	OR	L			; ... ZERO
	JR	Z,VGA_FILL3		; ALL DONE
	DEC	HL			; DEC COUNT
	EX	(SP),HL			; HL = CHAR/ATTR, COUNT ON STACK


	OUT	(C),E			; SET LO ADDR
	INC	C			; POINT TO DATA REG

	OUT	(C),H			; OUTPUT CHAR
	INC	E			; INC ADDR
	DEC	C			; POINT TO LO ADDR REG
	OUT	(C),E			; UPDATE LO ADDR
	INC	C			; POINT TO DATA REG
	OUT	(C),L			; OUTPUT ATTR

	DEC	C			; POINT TO LO ADDR REG
	INC	E			; INC ADDR LO
	JR	NZ,VGA_FILL2		; IF NO CF, SHORT LOOP
	
	DEC	C			; POINT TO HI ADDR REG
	INC	D			; INC ADDR HI
	JR	VGA_FILL1		; FULL LOOP

VGA_FILL3:
	POP	DE			; CLEAR STACK
	RET
;
;----------------------------------------------------------------------
; SCROLL ENTIRE SCREEN FORWARD BY ONE LINE (CURSOR POSITION UNCHANGED)
;----------------------------------------------------------------------
;
VGA_SCROLL:
	; CLEAR LINE ABOUT TO BE EXPOSED
	LD	DE,(VGA_POS)
	PUSH	DE
	LD	DE,0 + (VGA_ROWS * VGA_COLS)
	LD	(VGA_POS),DE
	LD	DE,VGA_COLS
	LD	A,' '
	CALL	VGA_FILL
	POP	DE
	LD	(VGA_POS),DE

	; USE BLOCK COPY TO SCROLL UP ONE LINE
	LD	HL,VGA_COLS
	LD	DE,0
	LD	BC,0 + ((VGA_ROWS) * VGA_COLS)
	CALL	VGA_BLKCPY
	
	RET
;
;----------------------------------------------------------------------
; REVERSE SCROLL ENTIRE SCREEN BY ONE LINE (CURSOR POSITION UNCHANGED)
;----------------------------------------------------------------------
;
VGA_RSCROLL:
	; USE BLOCK COPY TO SCROLL DOWN ONE LINE
	LD	HL,0 + ((VGA_ROWS - 1) * VGA_COLS) - 1	; SRC IS EOS - 1 LINE
	LD	DE,0 + ((VGA_ROWS) * VGA_COLS) - 1	; DEST IS EOS
	LD	BC,0 + ((VGA_ROWS - 1) * VGA_COLS)	; LENGTH IS ROWS - 1
	CALL	VGA_RBLKCPY
	
	; CLEAR TOP LINE
	LD	DE,(VGA_POS)
	PUSH	DE
	LD	DE,0
	LD	(VGA_POS),DE
	LD	DE,VGA_COLS
	LD	A,' '
	CALL	VGA_FILL
	POP	DE
	LD	(VGA_POS),DE

	RET
;
;----------------------------------------------------------------------
; BLOCK COPY BC BYTES FROM HL TO DE
;----------------------------------------------------------------------
;
VGA_BLKCPY:
	; ADJUST POINTERS FOR 2 BYTE WIDTH (CHAR & ATTR)
	RL	E
	RL	D
	RL	L
	RL	H

VGA_BLKCPY1:

	PUSH	BC		; SAVE COUNT
	
	; BA = (HL), HL INCREMENTED
	LD	C,VGA_HI	; C := VGA_HI
	OUT	(C),H		; VGA_HI := SOURCE HI (H)
	INC	C		; C := VGA_LO
	OUT	(C),L		; VGA_LO := SOURCE LO (L)
	INC	C		; C := VGA_DATA
	IN	B,(C)		; B := EVEN DATA BYTE (CHAR)
	INC	HL		; INC SOURCE PTR
	DEC	C		; C := VGA_LO
	OUT	(C),L		; VGA_LO := SOURCE LO (L), VGA_HI IS UNCHANGED!
	INC	C		; C := VGA_DATA
	IN	A,(C)		; A := ODD DATA BYTE (ATTR)
	INC	HL		; INC SOURCE PTR
	
	; (DE) = BA, DE INCREMENTED
	LD	C,VGA_HI	; C := VGA_HI
	OUT	(C),D		; VGA_HI := DEST HI (D)
	INC	C		; C := VGA_LO
	OUT	(C),E		; VGA_LO := DEST LO (E)
	INC	C		; C := VGA_DATA
	OUT	(C),B		; EVEN DATA BYTE (CHAR) := B
	INC	DE		; INC DEST PTR
	DEC	C		; C := VGA_LO
	OUT	(C),E		; VGA_LO := DEST LO (E), VGA_HI IS UNCHANGED
	INC	C		; C := VGA_DATA
	OUT	(C),A		; ODD DATA BYTE (ATTR) := A
	INC	DE		; INC DEST PTR

	; CHECK COUNT AND LOOP TILL DONE
	POP	BC		; RECOVER COUNT
	DEC	BC		; DEC COUNT
	LD	A,B		; CHECK COUNT
	OR	C		; ... FOR ZERO
	JR	NZ,VGA_BLKCPY1	; LOOP TILL DONE

	RET			; DONE
;
VGA_RBLKCPY:
	; ADJUST POINTERS FOR 2 BYTE WIDTH (CHAR & ATTR)
	RL	E
	RL	D
	RL	L
	RL	H
	
	; ADJUST TO POINT TO SECOND BYTE OF PAIR (ATTR)
	INC	E
	INC	L

VGA_RBLKCPY1:

	PUSH	BC		; SAVE COUNT
	
	; BA = (HL), HL INCREMENTED
	LD	C,VGA_HI	; C := VGA_HI
	OUT	(C),H		; VGA_HI := SOURCE HI (H)
	INC	C		; C := VGA_LO
	OUT	(C),L		; VGA_LO := SOURCE LO (L)
	INC	C		; C := VGA_DATA
	IN	A,(C)		; A := ODD DATA BYTE (ATTR)
	DEC	HL		; DEC SOURCE PTR
	DEC	C		; C := VGA_LO
	OUT	(C),L		; VGA_LO := SOURCE LO (L), VGA_HI IS UNCHANGED!
	INC	C		; C := VGA_DATA
	IN	B,(C)		; B := EVEN DATA BYTE (CHAR)
	DEC	HL		; DEC SOURCE PTR
	
	; (DE) = BA, DE INCREMENTED
	LD	C,VGA_HI	; C := VGA_HI
	OUT	(C),D		; VGA_HI := DEST HI (D)
	INC	C		; C := VGA_LO
	OUT	(C),E		; VGA_LO := DEST LO (E)
	INC	C		; C := VGA_DATA
	OUT	(C),A		; ODD DATA BYTE (ATTR) := A
	DEC	DE		; DEC DEST PTR
	DEC	C		; C := VGA_LO
	OUT	(C),E		; VGA_LO := DEST LO (E), VGA_HI IS UNCHANGED
	INC	C		; C := VGA_DATA
	OUT	(C),B		; EVEN DATA BYTE (CHAR) := B
	DEC	DE		; DEC DEST PTR

	; CHECK COUNT AND LOOP TILL DONE
	POP	BC		; RECOVER COUNT
	DEC	BC		; DEC COUNT
	LD	A,B		; CHECK COUNT
	OR	C		; ... FOR ZERO
	JR	NZ,VGA_RBLKCPY1	; LOOP TILL DONE

	RET			; DONE
;
;==================================================================================================
;   VGA DRIVER - DATA
;==================================================================================================
;
VGA_ATTR	.DB	0	; CURRENT COLOR
VGA_POS		.DW 	0	; CURRENT DISPLAY POSITION
VGA_CFGV	.DB	0	; CURRENT BOARD CONFIG VALUE
VGA_RUB		.DB	0	; REVERSE/UNDERLINE/BLINK (-----RUB)
;
; ATTRIBUTE ENCODING:
;   BIT 7: ALT FONT
;   BIT 6: BG REG
;   BIT 5: BG GREEN
;   BIT 4: BG BLUE
;   BIT 3: FG INTENSITY
;   BIT 2: FG RED
;   BIT 1: FG GREEN
;   BIT 0: FG BLUE
;
;===============================================================================
; DEFAULT REGISTER VALUES
;===============================================================================
;
REGS_VGA:
	.DB	0,100 - 1	; HORZ TOT - 1
	.DB	1,80		; HORZ DISP
	.DB	2,80 + 2	; HORZ DISP + HORZ FP
	.DB	3,(2 << 4) | (12 & $0F)	; VERT SW, HORZ SW
	.DB	4,28 - 1	; VERT TOT - 1
	.DB	5,1		; VERT TOT ADJ
	.DB	6,25		; VERT DISP
	.DB	7,25 + 1	; VERT DISP + VERT FP
	.DB	9,16 - 1	; CHAR HEIGHT - 1
	.DB	10,(13 | $60)	; CURSOR START & CURSOR BLINK
	.DB	11,14		; CURSOR END
	.DB	12,($0000 >> 8) & $FF	; SCRN 1 START (HI)
	.DB	13,($0000 & $FF)	; SCRN 1 START (LO)
	.DB	30,0		; CONTROL 1
	.DB	31,0		; CONTROL 2
	.DB	33,0		; CONTROL 3
	.DB	$FF		; END MARKER
;
;==================================================================================================
;   VGA DRIVER - INSTANCE DATA
;==================================================================================================
;
VGA_IDAT:
	.DB	VGA_KBDST
	.DB	VGA_KBDDATA