; Dump of M873-YA boot roms
; 23-044A2, 23-045A2

; Entry point -- RF11 disk

173000 010702		MOV	PC, R2
173002 000464		BR	DOSIMP
173004 177462					; RFWC
173006 000005

; Entry point -- RK11 disk

173010 010702		MOV	PC, R2
173012 000460		BR	DOSIMP
173014 177406					; RKWC
173016 000005		

; Entry point -- contents of console switch register

173020 013707		MOV	@#177570, PC
173022 177570		

; New PC/PS pair for forced boot in non-volatile memory system
;
; Note that the new PC points off the end of the ROM in the -YA;
; it's not clear that these will actually be used, since in a normal
; power-on the M873 doesn't play with the PS/PC fetch; and in PS/PC
; fetches caused by actuating the BM783 via one of its input lines,
; the data in the PC fetch is specially provided by the card (from
; the address specified by the appropriate diode array)

173024 173776		
173026 000340		

; Entry point -- TC11 DECtape

173030 010702		MOV	PC, R2
173032 000426		BR	DOEXT

173034 177344					; TCWC
173036 004003		
173040 100000		
173042 024000		
173044 000445		
173046 000005

; Entry point -- TM11 magnetic tape

173050 010702		MOV	PC, R2
173052 000416		BR	DOEXT

173054 172524					; TMBC
173056 060017		
173060 000200		
173062 100000		
173064 000413		
173066 060011		
173070 000200		
173072 100000		
173074 000431		
173076 060003		

; Entry point -- RP11 disk

173100 010702		MOV	PC, R2
173102 000424		BR	DOSIMP
173104 176716					; RPWC
173106 000005		


; General extended read routine read routine for more complex devices
; (such as tape  drives); called with pointer to word before words
; containing the device register and various commands, results, etc
; in R2

173110 010200	DOEXT:	MOV	R2, R0
173112 005720		TST	(R0)+
173114 000005		RESET				; ALso clears BAR
173116 005720		TST	(R0)+
173120 016201		MOV	2(R2), R1		; Get device register
173122 000002		
173124 005311		DEC	@R1
173126 012041		MOV	(R0)+, -(R1)
173130 031011	1$:	BIT	@R0, @R1
173132 001776		BEQ	1$
173134 005720		TST	(R0)+
173136 032041		BIT	(R0)+, -(R1)
173140 001063		BNE	xxx
173142 000110		JMP	@R0


; Entry point -- RC11 disk

173144 010702		MOV	PC, R2
173146 000402		BR	DOSIMP
173150 177450		
173152 000005		


; General read routine read routine for 'simple' devices (such as disk
; drives); called with pointer to word before pair of words containing
; the device's Word Count register and 'Read Go' command in R2

173154 010200	DOSIMP:	MOV	R2, R0		; Get command pointer
173156 005720		TST	(R0)+
173160 005720		TST	(R0)+
173162 000005		RESET			; Also clears device BAR
173164 016201		MOV	2(R2), R1	; Get addr of WC reg
173166 000002		
173170 012711		MOV	#177000, @R1	; Set word count
173172 177000		
173174 011041		MOV	@R0, -(R1)	; Command
173176 105711	1$:	TSTB	@R1		; Wait for done
173200 100376		BPL	1$
173202 005711		TST	@R1		; Check error bit, jump to
173204 100441		BMI	xxx		; xxx if set, otherwise
173206 005007		CLR	PC		; jump to newly loaded code


; Entry point -- KL11/DL11 serial line; low speed paper tape reader

173210 012704		MOV	#177560, R4	; Low speed reader address
173212 177560		
173214 000440		BR	RDBOOT

; ??

173216 017640		
173220 002415		
173222 112024		

; New power-fail/resume PC/PS pair for boot in volatile memory system
; See comments under PC/PS pair for non-volatile memory, at 173024

173224 173776		
173226 000340		

; Entry point -- TA11 casette tape

173230 005004		CLR	R4
173232 012700		MOV	#177500, R0
173234 177500		
173236 000005		RESET
173240 010410		
173242 012701		MOV	#173216, R1
173244 173216		
173246 012702		MOV	#375, R2
173250 000375		
173252 112103		MOVB	(R1)+, R3
173254 112110		MOVB	(R1)+, @R0
173256 100407		BMI	1$
173260 130310	2$:	BITB	R3, @R0
173262 001776		BEQ	2$
173264 105202		INCB	R2
173266 100772		BMI	xx
173270 116012		SUB	2(R0), @R2
173272 000002		
173274 000771		BR	yy
173276 005710	1$:	TST	@R0
173300 100756		BMI	xx
173302 005002		CLR	R2
173304 120312		CMPB	R3, @R2
173306 001377		BNE	.		; Loop on error?
173310 000112		JMP	@R2

; Entry point -- PC11 high speed paper tape reader

173312 012704		MOV	#177550, R4	; High speed read address
173314 177550					; Falls through


; Paper tape read routine; first sizes memory, then loads bootstrap
; format tape.
;
; The memory sizing assumes contiguous lower memory; the way it works
; is that the two instruction sequence, setting the SP and then the
; auto-decrement store, will continuously execute (via NXM traps)
; until some memory is found that responds. (Note that the data being
; stored is the device CSR, which by convention is in the high word in
; memory with the bootloader). The code then falls through into
; the code below, which sets up the memory for the incoming program in
; bootstrap format (usually the absolute loader).
;
; That code is extemely 'tense'; the stack location was chosen such
; that, when ANDed with the top of memory (which should be of the form
; xxx776), it produces the location of the load location offset,
; used by bootload format to self-modify the bootloader to i) start
; depositing data, and later ii) to branch to the start of the recently
; loaded code. Here, it is an actual pointer, not an offset, but the
; low byte of it is still modified in the same way, to the same ends.
;
; There is no bootloader here, of course, but this code notices when
; the high byte of the notional 'BR' at the end of the 'bootloader'
; is modified at the end of the bootload process, and finishes creating
; an actual BR there, and jumps to it.
;
; That all won't work properly unless the bootloader format tape has at
; least one 0 pad byte on the end (after the two bytes that, with the
; actual bootloader, over-write the low byte of the BR at the end of the
; bootloader), for two reasons. i) The code above only notices when
; the _high_ byte of the branch is written, which will be by the first
; 0 pad byte; and ii) unless that byte in memory is a zero - and this
; code does not clear memory - the INCB at the end will not create a 'BR'
; instruction there.

173316 000005	RDBOOT:	RESET
173320 012701		MOV	#160000, R1	; Start at top of address
173322 160000					; space, looking for memory
173324 012702		MOV	#6, R2		; Set up NXM vector
173326 000006		
173330 012712		MOV	#340, @R2
173332 000340		
173334 010742		MOV	PC, -(R2)	; On fault, go to next inst

173336 012706		MOV	#24, SP		; Set up stack at special location;
173340 000024					; happens to be power fail vector
173342 010441		MOV	R4, -(R1)	; Store data

173344 040601		BIC	SP, R1		; Get bootloader load offset
173346 010111		MOV	R1, @R1		; Store it there

173350 011102	2$:	MOV	@R1, R2		; Get location to store in
173352 005214		INC	@R4		; Turn reader on
173354 105714	1$:	TSTB	@R4		; Wait for next byte to be there
173356 100376		BPL	1$
173360 116412		MOVB	2(R4), @R2	; Get byte and save it
173362 000002		
173364 005211		INC	@R1		; Increment save location
173366 120227		CMPB	R2, #375	; Did we just finish
173370 000375					; over-writing the 'BR'?
173372 001366		BNE	2$		; No, keep going

173374 105222		INCB	(R2)+		; Turn that location into a 'BR'
173376 000142		JMP	-(R2)		; And jump to it