.title	M9312 'DK/DT' BOOT prom for RK03/05 and TU55/56 controllers

	; This source code is a modified copy of the DEC M9312 23-756A9 boot PROM.
	;
	; This boot PROM is for the RK03/05 DECdisk controllers.
	;
	; Multiple units and/or CSR addresses are supported via different entry points.

rkcsr	=177400				; std RK03/05 DECdisk csrbase

rkwc	=+6-4				; word count
rkda	=+12-4				; disk address

xxwc	=rkwc				; common word count offset

	.asect
	; ---- Simple boot drive 0 from 0
	. = 0
	jmp	@#start0

	; ---- Reboot drive 0 on power event
	. = 24				; Power ON/OFF
	.word	     start0		; PC
	.word	     340		; PSW priority level 7


	; ----- Main boot addresses
	.=10000 			;  arbitrary position > 3000

start:
	; 8 unit numbers => 8 entry addresses
start0:
	mov	#0,r0
	br	dknr
	nop
start1:
	mov	#1,r0
	br	dknr
	nop
start2:
	mov	#2,r0
	br	dknr
	nop
start3:
	mov	#3,r0
	br	dknr
	nop
start4:
	mov	#4,r0
	br	dknr
	nop
start5:
	mov	#5,r0
	br	dknr
	nop
start6:
	mov	#6,r0
	br	dknr
	nop
start7:
	mov	#7,r0
	br	dknr
	nop


dknr:
	mov	#rkcsr+4,r1		; boot std csr, unit <R0>

	mov	r0,r3			; get unit number
	clc				; C=0 for ror
	ror	r3			; shift into 15:12
	ror	r3			;
	ror	r3			;
	ror	r3			;
	mov	r3,rkda(r1)		; unit number, sector 0 to disk addr

	mov	#-512.,xxwc(r1)		; set word count
	bis	#5,r3			; command READ+GO
	mov	r3,(r1)			; execute
2$:	tstb	(r1)			; test ready
	bpl	2$			; loop

	tst	(r1)			; check error
	bpl	3$			; br if no error

	reset				; reset the world
	br     dknr			; and retry

3$:	bic	#377,(r1)		; nop command
	clr	pc			; jump to loaded boot sector

	.end