gistfile1.asm

; Name: romImage.s
; Author: Quinn Dunki
; Copyright: ©2012 Quinn Dunki
; License: All Rights Reserved
;
; 6052 code for Veronica's main system ROM
; For details, see http://www.quinndunki.com/blondihacks
;
; Zero Page:
;    $00..$01:	Subroutine parameter 1
;	$10..$11:	Scratch

;
; GPU commands:
;
CLEARSCR = $01
PLOTCHAR = $02
PLOTSTR = $03
FONTFGCLR = $04
FONTBGCLR = $05
CURSORXPOS = $06
CURSORYPOS = $07

.macro GPUCMD	cmdByte,paramByte
	lda		#cmdByte
	sta		$efff
	lda		#paramByte
	sta		$efff
.endmacro


;
; Function calling
;
.macro CALL16	subroutine,param16
	lda		#<param16
	sta		$00
	lda		#>param16
	sta		$01
	jsr		subroutine
.endmacro


;
; Constants:
;
GPUREG = $efff		; GPU command and status register
RAMSTART_LO = $00	; First valid RAM location, after stack
RAMSTART_HI = $02
RAMEND_LO = $01		; Last valid RAM location +1
RAMEND_HI = $e0
TESTVALUE = $42		; Bit pattern written and read to test RAM locations


;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; Veronica main system ROM
;
; Boot entry point: $F000
;
.org $f000

	jsr		delay		; Give GPU time to boot and achieve VGA lock
	jsr		delay
	jsr		delay

ramCheck:
	GPUCMD	CLEARSCR,$00	; Show introduction text
	GPUCMD	FONTFGCLR,$3f
	GPUCMD	FONTBGCLR,$00

	CALL16	printStr,prompt

	GPUCMD	CURSORXPOS,$00
	GPUCMD	CURSORYPOS,$01

	lda		#RAMSTART_LO		; Initialize test address
	sta		$00
	lda		#RAMSTART_HI
	sta		$01

	lda		#$00
	sta		$10			; Initialize page counters
	sta		$11			; BCD version

ramCheckLoop:
	ldy		#$00		; Store and retrieve the test value
	lda		#TESTVALUE
	sta		($00),y

	lda		#$00
	lda		($00),y
	cmp		#TESTVALUE
	beq		ramCheckNextAddr
	jmp		ramCheckFail

ramCheckNextAddr:
	inc		$00			; Increment the 16-bit test address
	bne		ramCheckThresholds
	inc		$01

ramCheckThresholds:
	lda		$01
	cmp		#RAMEND_HI		; Have we reached the last address?
	bne		ramCheckPage
	lda		$00
	cmp		#RAMEND_LO
	beq		ramCheckSuccess

ramCheckPage:
	ldy		$01			; Have we advanced another K?
	dey
	dey
	tya
	lsr		a
	lsr		a
	cmp		$10
	beq		ramCheckLoop

	sta		$10
	sed					; Increment BCD version of page counter
	clc
	lda		$11
	adc		#$01
	sta		$11
	cld

	ldy		#PLOTSTR		; Update display
	sty		GPUREG
	pha
	lsr		a
	lsr		a
	lsr		a
	lsr		a
	ora		#'0'
	sta		GPUREG

	ldy		#PLOTSTR
	sty		GPUREG
	pla
	and		#$0f
	ora		#'0'
	sta		GPUREG

	lda		#PLOTSTR
	sta		GPUREG
	lda		#'K'
	sta		GPUREG

	GPUCMD	CURSORXPOS,$00
	GPUCMD	CURSORYPOS,$01
	jmp		ramCheckLoop

ramCheckSuccess:
	GPUCMD	CURSORXPOS,$00	; Print success message
	GPUCMD	CURSORYPOS,$02
	GPUCMD	FONTFGCLR,$0c

	CALL16	printStr,success

	jmp		spinlock

ramCheckFail:	; Print failure message
	GPUCMD	CURSORXPOS,$00
	GPUCMD	CURSORYPOS,$02
	GPUCMD	FONTFGCLR,$00
	GPUCMD	FONTBGCLR,$30

	CALL16	printStr,failure

	jmp		spinlock


;;;;;;;;;;;;;;;;;;;;;;;
; printStr
; Renders a null-terminated string at the current cursor location
; Args: $0000: Address of string
;
printStr:
	ldy		#$00

printStrLoop:
	lda		($00),y		; Render the next character
	beq		printStrNull
	tax
	lda		#PLOTSTR
	sta		GPUREG
	txa
	sta		GPUREG

	inc		$00			; Increment pointer
	bne		printStrLoop
	inc		$01
	jmp		printStrLoop

printStrNull:
	rts


;;;;;;;;;;;;;;;;;;;;;;;
; delay
; Sleeps for ~1 second
; Args: None
;
delay:
	pha				; Save registers
	tya
	pha
	txa
	pha

	ldy		#$ce	; Loop a bunch
delayOuter:
	ldx		#$ff
delayInner:
	nop
	nop
	nop
	nop
	nop
	nop
	nop
	dex
	bne		delayInner
	dey
	bne		delayOuter

	pla				; Restore registers
	tax
	pla
	tay
	pla
	rts


;;;;;;;;;;;;;;;;;;;;;;;
; spinLock
; Stalls CPU indefinitely
; Args: N/A
;
spinlock:
	jmp		spinlock


;;;;;;;;;;;;;;;;;;;;;;;
; Static strings
;
prompt:
.byte		"VERONICA RAM CHECK",$00
success:
.byte		"SUCCESS",$00
failure:
.byte		"FAILED",$00