Add loader.s

wip-duuqnd/loader.s

@@ -0,0 +1,112 @@
+;;; -*- Mode: asm; indent-tabs-mode: t; tab-width: 8 -*-
+
+	CLKMASK	=	%00000010
+	CTRL2	=	$DC00
+
+coldstart:
+	lda #$0
+	sta $400
+waitstart:
+	lda $dc01
+	and #$01
+	bne waitstart
+	lda #$00
+	sta $d020
+teststart:
+	jsr check_for_load_start
+	jmp $c000
+	beq teststart
+	bcs @error
+	jmp $c000
+@error:
+	lda #0
+	sta $0400
+	rts
+
+check_for_load_start:
+	lda #CLKMASK
+	bit CTRL2
+	bne start
+	lda #$00
+	rts
+start:
+	sei
+	ldx #$02
+	stx $d020
+	ldy #$00
+	jmp new_byte
+
+wait_for_bit_start:
+	lda #CLKMASK
+@loop:
+	bit CTRL2
+	beq @loop
+
+	lda #CLKMASK
+	bit CTRL2
+	beq error
+	lda CTRL2
+
+	lsr
+	ror BYTE
+	bcc wait_for_bit_end
+	txa			; get the zero flag from X
+	beq @normal
+	dex
+	lda BYTE
+	sta LEN,x
+	txa
+	bne @notdone
+	;; Computing stop address
+	clc
+	lda LEN
+	adc z:progdest
+	sta stop
+	lda LEN+1
+	adc z:progdest+1
+	sta stop+1
+	jmp @notdone
+@normal:
+	;; Byte finished, storing
+	lda BYTE
+	sta (progdest), y
+	inc z:progdest
+	bne @noinchi
+	inc z:progdest+1
+@noinchi:
+	;; Comparing progdest against stop address
+	lda z:progdest
+	cmp stop
+	bne @notdone
+	lda z:progdest+1
+	cmp stop+1
+	bne @notdone
+	jmp done
+@notdone:
+new_byte:
+	lda #%10000000
+	sta BYTE
+wait_for_bit_end:
+	lda #CLKMASK
+@loop:
+	bit CTRL2
+	bne @loop
+	jmp wait_for_bit_start
+
+done:
+	lda #$01
+	cli
+	clc
+	rts
+
+error:
+	;; TODO
+	cli
+	sec
+	rts
+
+BYTE		= $400
+LEN		= $402
+progdest	= $fe
+stop:		.word $0000
+loaded:		.byte 0