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[fpgaboy.git] / xm.asm

	SECTION "wee",HOME[$0]
	; this all needs to be PIC!
;	xor a
;	ld hl, $FF60
;	ld [hli], a
;	ld [hli], a
;	ld [hli], a
st:	ld sp, $CFFF
nak:
	ld a, $15	; NAK
	call putc+$FF80
	
.ack:	call getc+$FF80
;	cp $01	;SOH
;	jr z,.soh
	cp $04	;EOT
	jr z, .eot
	cp $18	;CAN
	jr z, .rst
	jr nak

.eot:
	ld A, $06	; Ack the EOT
	call putc+$FF80
.rst:	rst $00

.soh:	call getc+$FF80	; blk
	call getc+$FF80	; iblk
	ld b, $00
	ld hl, $C000
.lp:	bit 7, l
	jr nz, .cksm
	call getc+$FF80
	ld [hli], a
	add b
	ld b, a
	jr .lp
.cksm:	call getc+$FF80
	cp b
	jr nz, .donak
	ld hl, $C000
.lp2:	ld a, [hli]
	ld [$FF63], A
	bit 7, l
	jr z,.lp2
.doack:	ld A, $06	; 06
	call putc+$FF80
	jr .ack
.donak:	call getc+$FF80		; Wait until the line clears, and then once
	jr .donak		; that happens, getc will cause a NAK.

getc:
	xor d
	;xor e	; Possibly not needed?
.dgetc:
	dec de
	xor a
	cp d
	jr z, .timeout
	ld a, [$FF53]
	and $02
	jr z, .dgetc
	ld a, [$FF52]
	ret
.timeout:
	ld hl, $D010
	ld a, [hl]
	inc a
	ld [hl], a
	ld [$FF51], a
	pop hl
	jr nak

putc:
	ld c, $53
	push af
.waitport:
	ld a,[c]
	and $01
	jr nz,.waitport
	pop af
	ld [$FF52],a
	ret

	section "a", HOME[$7E]
	nop