Add original unix v6

source/mdec/ht.s

@@ -0,0 +1,70 @@
+htcs1 = 172440
+htba  = 172444
+htfc  = 172446
+htcs2 = 172450
+htds  = 172452
+httc  = 172472
+
+P800 = 1300
+P1600 = 2300
+PIP = 20000
+MOL = 10000
+ERR = 40000
+REV = 33
+READ = 71
+REW = 7
+
+tread:
+1:
+	mov	ba,mtma
+	cmp	mtapa,tapa
+	beq	1f
+	bhi	2f
+	jsr	pc,rrec
+	br	1b
+2:
+	jsr	pc,rew
+	br	1b
+1:
+	mov	wc,r1
+1:
+	jsr	pc,rrec
+	add	$256.,r1
+	bmi	1b
+	rts	pc
+
+rrec:
+	mov	$htds,r0
+	tstb	(r0)
+	bpl	rrec
+	bit	$PIP,(r0)
+	bne	rrec
+	bit	$MOL,(r0)
+	beq	rrec
+	mov	$htfc,r0
+	mov	$-512.,(r0)
+	mov	mtma,-(r0)
+	mov	$-256.,-(r0)
+	mov	$READ,-(r0)
+1:
+	tstb	(r0)
+	bpl	1b
+	bit	$ERR,*$htds
+	bpl	1f
+	mov	$-1,*$htfc
+	mov	$REV,(r0)
+	br	rrec
+1:
+	add	$512.,mtma
+	inc	mtapa
+	rts	pc
+
+rew:
+	clr	*$htcs2
+	mov	$P800,*$httc
+	mov	$REW,*$htcs1
+	clr	mtapa
+	rts	pc
+
+mtapa:	0
+mtma:	0