1                                	.title	M9312 'DX' BOOT prom for RX11 compatible controller
       2                                
       3                                	; This source code is an exact copy of the DEC M9312 23-753A9 boot PROM.
       4                                	;
       5                                	; This boot PROM is for any RX11/RX01 compatible floppy controller.
       6                                	;
       7                                	; Multiple units and/or CSR addresses are supported via different entry points.
       8                                	;
       9                                	; Standard devices are 82S131, Am27S13, 74S571 or other compatible bipolar
      10                                	; PROMs with a 512x4 TriState 16pin DIP architecture. This code resides in
      11                                	; the low half of the device; the top half is blank and unused.
      12                                	;
      13                                	; Alternatively, 82S129 compatible 256x4 TriState 16pin DIP devices can be
      14                                	; used, as the uppermost address line (hardwired low) is an active low chip
      15                                	; select (and will be correctly asserted low).
      16                                
      17 177170                         rxcsr	=177170				; std RX11 csrbase
      18                                
      19 000000                         rxcs	=+0				; command/status
      20 000002                         rxdb	=+2				; data buffer
      21                                
      22 165564                         diags	=165564				; console diags phase2 entry
      23                                
      24                                	.asect
      25 173000                         	.=173000
      26                                
      27                                	; --------------------------------------------------
      28                                
      29 173000    130     104          start:	.ascii	"XD"			; device code (reversed)
      30                                
      31 173002 000176                  	.word	last-.			; offset to next boot header
      32                                
      33 173004 000261                  dx0n:	sec				; boot std csr, unit zero, no diags
      34 173006 012700  000000          dx0d:	mov	#0,r0			; boot std csr, unit zero, with diags
      35 173012 012701  177170          dxNr:	mov	#rxcsr,r1		; boot std csr, unit <R0>
      36 173016 010704                  dxNb:	mov	pc,r4			; boot csr <R1>, unit <R0>
      37 173020 103056                  	bcc	diag			; br if diags requested
      38 173022 000402                  	br	go			; return to (R4)+2 from diags
      39                                					; then skip over pseudo reboot vector
      40                                
      41                                	; --------------------------------------------------
      42                                
      43 173024 173000                  	.word	173000			; prom start addess @ 24
      44 173026 000340                  	.word	340			; and priority level @ 26
      45                                
      46                                	; --------------------------------------------------
      47                                
      48 173030 000241                  go:	clc				; clear carry
      49 173032 012703  001407          	mov	#<003*400>+007,r3	; unit zero, read+go
      50 173036 132700  000001          	bitb	#1,r0			; test unit ID
      51 173042 001402                  	beq	2$			; br if zero
      52 173044 012703  011427          	mov	#<023*400>+027,r3	; unit one, read+go
      53                                
      54 173050 132711  100040          2$:	bitb	#100040,(r1)		; test error<15> or done<5>
      55 173054 001775                  	beq	2$			; neither, keep looping
      56                                
      57 173056 110311                  	movb	r3,(r1)			; exec read+go on unit
      58                                
      59 173060 111105                  3$:	movb	(r1),r5			; wait for transfer req
      60 173062 100376                  	bpl	3$			; not yet, keep looping
      61                                
      62 173064 112761  000001  000002  	movb	#1,rxdb(r1)		; set track/sector 1
      63 173072 106003                  	rorb	r3			; 007 -> 003 -> 001 -> 000
      64 173074 102771                  	bvs	3$			; loop three times
      65                                
      66 173076 032711  100040          4$:	bit	#100040,(r1)		; test error<15> or done<5>
      67 173102 001775                  	beq	4$			; neither, keep looping
      68 173104 100412                  	bmi	6$			; br if error
      69                                
      70 173106 000303                  	swab	r3			; R3=003/023 unit0/1
      71 173110 110311                  	movb	r3,(r1)			; exec emptybuf+go on unit
      72                                
      73 173112 005003                  	clr	r3			; bus address ptr
      74 173114 105711                  5$:	tstb	(r1)			; wait for data transfer req
      75 173116 100376                  	bpl	5$			; loop if not yet
      76 173120 116123  000002          	movb	rxdb(r1),(r3)+		; store data byte
      77 173124 105703                  	tstb	r3			; check address >= 128
      78 173126 100372                  	bpl	5$			; br if address in 0..127
      79                                
      80 173130 005007                  	clr	pc			; jump to bootstrap at zero
      81                                
      82 173132 000005                  6$:	reset				; failed, reset controller
      83 173134 000164  000002          	jmp	2(r4)			; and retry from the beginning
      84                                
      85                                	; --------------------------------------------------
      86                                
      87 173140 012700  000001          dx1n:	mov	#1,r0			; boot std csr, unit one, no diags
      88 173144 000261                  	sec				;
      89 173146 000721                  	br	dxNr			; continue
      90                                
      91 173150 012700  000001          dx1d:	mov	#1,r0			; boot std csr, unit one, ? diags
      92 173154 000716                  	br	dxNr			; continue
      93                                
      94                                	; --------------------------------------------------
      95                                
      96 173156 000137  165564          diag:	jmp	@#diags			; jump to console diags
      97                                
      98                                	; --------------------------------------------------
      99                                
     100 173162 000000  000000  000000  	.word	0,0,0,0,0,0		; unused
         173170 000000  000000  000000  
     101                                
     102                                	; --------------------------------------------------
     103                                
     104 173176                         	.=start+176
     105 173176 105572                  crc16:	.word	<105572>		; CRC-16 will go here
     106                                
     107                                last:	; next boot prom starts here
     108                                
     109                                	.end
     109