PDP-11 Bootstrap Loader - Revision history

Jdl: Slightly clearer description of xx

2025-03-05T04:48:40Z

Slightly clearer description of xx

← Older revision		Revision as of 04:48, 5 March 2025
Line 38:		Line 38:
	</pre>		</pre>

	When inputting the bootstrap program, the first ~~word is loaded~~ at location xx7744, where xx is replaced with the		When inputting the bootstrap program, the first instruction should be placed at location xx7744,
	address of the highest memory bank available according to the following table:		where xx is replaced with the address of the highest memory bank available according to the following table:

	{\| class="wikitable" style="text-align:center;"		{\| class="wikitable" style="text-align:center;"

Jdl: Transfer byte to buffer, not word

2025-03-05T04:39:36Z

Transfer *byte* to buffer, not word

← Older revision		Revision as of 04:39, 5 March 2025
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	xx7756 105711 WAIT: TSTB @R1 ; Wait until data available		xx7756 105711 WAIT: TSTB @R1 ; Wait until data available
	xx7760 100376 BPL WAIT		xx7760 100376 BPL WAIT
	xx7762 116162 MOVB 2(R1), LOAD(R2) ; Transfer ~~word~~ to buffer		xx7762 116162 MOVB 2(R1), LOAD(R2) ; Transfer byte to buffer
	xx7764 000002		xx7764 000002
	xx7766 xx7400		xx7766 xx7400

Jdl: Replaced bootstrap code with valid macro11 assembly that more closely matches the DEC documentation. Replaced "0x" placeholder text with "xx" to avoid confusion with C hex prefix. Added tables of possible xx and yyyyyy values.

2025-03-05T04:36:47Z

Replaced bootstrap code with valid macro11 assembly that more closely matches the DEC documentation. Replaced "0x" placeholder text with "xx" to avoid confusion with C hex prefix. Added tables of possible xx and yyyyyy values.

@@ Line 16: / Line 16: @@
 This is the actual bootstrap program:
- 	LOAD = 0x7400				; Buffer address
+<pre>
-x7744	016701	BEGIN:	MOV	DEVICE, R1	; Get Device CSR
+                        LOAD=xx7400          ; Buffer start address
-x7746	000026
-x7750	012702	LOOP:	MOV	(PC)+, R2	; Get buffer offset
+                        .=LOAD+0344          ; Start address of bootstrap loader (xx7744)
-x7752	000352	OFFSET:	.-LOAD
-x7754	005211		INC	@R1		; Turn on reader
+xx7744  016701  START:  MOV DEVICE, R1       ; Get reader CSR address
-x7756	105711	READY:	TSTB	@R1		; Done?
+xx7746  000026
-x7760	100376		BPL	READY
+xx7750  012702  LOOP:   MOV #.-LOAD+2, R2    ; Get buffer pointer
-x7762	116162		MOVB	2(R1), LOAD(R2)	; Transfer
+xx7752  000352                               ;   (<--- pointer to buffer)
-x7764	000002
+xx7754  005211          INC @R1              ; Enable the paper tape reader
-x7766	0x7400
+xx7756  105711  WAIT:   TSTB @R1             ; Wait until data available
-x7770	005267		INC	OFFSET		; Bump buffer offset
+xx7760  100376          BPL WAIT
-x7772	177756
+xx7762  116162          MOVB 2(R1), LOAD(R2) ; Transfer word to buffer
-x7774	000765		BR	LOOP
+xx7764  000002
-x7776	yyyyyy	DEVICE:	yyyyyy			; Input device CSR address
+xx7766  xx7400
 ==Bootstrap Loader format==

Jnc: Better cat

2023-11-16T17:52:20Z

Better cat

← Older revision		Revision as of 17:52, 16 November 2023
Line 54:		Line 54:
	The Bootstrap Loader is documented in some detail in the "paper tape software programming handbook" (DEC-11-GGPB-D), pp. 6-1 to 6-8.		The Bootstrap Loader is documented in some detail in the "paper tape software programming handbook" (DEC-11-GGPB-D), pp. 6-1 to 6-8.

	[[Category: PDP-~~11s~~]]		[[Category: PDP-11 Software]]
	[[Category: PDP-11 File Formats]]		[[Category: PDP-11 File Formats]]

Jnc: +cat

2022-04-05T21:02:15Z

+cat

← Older revision		Revision as of 21:02, 5 April 2022
Line 1:		Line 1:
	The '''PDP-11 Bootstrap Loader''' is a short [[program]] designed to be loaded into the [[main memory]] on a [[PDP-11]] via the [[front panel]]; it is then run to load an initial program into the machine. I.e it is a way of [[bootstrap]]ping a totally empty machine, one with no [[Read-only memory\|ROM]].		The '''PDP-11 Bootstrap Loader''' is a short [[program]] designed to be loaded into the [[main memory]] on a [[PDP-11]] via the [[front panel]]; it is then run to load an initial program into the machine. I.e. it is a way of [[bootstrap]]ping a totally empty machine, one with no [[Read-only memory\|ROM]].

	It is designed to be absolutely as short as possible (since it is manually toggled in via the [[switch register]]), and therefore has limitations, including how long a program can be loaded using it, and where in memory that program can be placed. The usual program to load with it is the [[PDP-11 Absolute Loader]], which relaxes both of those limitations.		It is designed to be absolutely as short as possible (since it is manually toggled in via the [[switch register]]), and therefore has limitations, including how long a program can be loaded using it, and where in memory that program can be placed. The usual program to load with it is the [[PDP-11 Absolute Loader]], which relaxes both of those limitations.
Line 11:		Line 11:
	The program starts with the pointer set to itself, so the blank leader at the start of the data for the bootstrap loader (originally contained on [[paper tape]]s) starts with a special leader code which causes this to be left un-changed.		The program starts with the pointer set to itself, so the blank leader at the start of the data for the bootstrap loader (originally contained on [[paper tape]]s) starts with a special leader code which causes this to be left un-changed.

	The buffer pointer is then modified to point it slightly before the ~~bootrap~~ loader in memory, so at the end of the load the newly loaded code then progressively overlays the first several [[instruction]]s of the bootstrap loader itself, finally patching the buffer pointer to point at the branch instruction, which is then modified to jump to the newly loaded code.		The buffer pointer is then modified to point it slightly before the bootstrap loader in memory, so at the end of the load the newly loaded code then progressively overlays the first several [[instruction]]s of the bootstrap loader itself, finally patching the buffer pointer to point at the branch instruction, which is then modified to jump to the newly loaded code.

	===Code===		===Code===
Line 53:		Line 53:

	The Bootstrap Loader is documented in some detail in the "paper tape software programming handbook" (DEC-11-GGPB-D), pp. 6-1 to 6-8.		The Bootstrap Loader is documented in some detail in the "paper tape software programming handbook" (DEC-11-GGPB-D), pp. 6-1 to 6-8.

	~~{{PDP-11}}~~

	[[Category: PDP-11s]]		[[Category: PDP-11s]]
			[[Category: PDP-11 File Formats]]

Jnc: /* Code */ Offset in symbolic form

2021-03-08T09:27:31Z

Code: Offset in symbolic form

← Older revision		Revision as of 09:27, 8 March 2021
Line 21:		Line 21:
	0x7746 000026		0x7746 000026
	0x7750 012702 LOOP: MOV (PC)+, R2 ; Get buffer offset		0x7750 012702 LOOP: MOV (PC)+, R2 ; Get buffer offset
	0x7752 000352 OFFSET: ~~0352~~		0x7752 000352 OFFSET: .-LOAD
	0x7754 005211 INC @R1 ; Turn on reader		0x7754 005211 INC @R1 ; Turn on reader
	0x7756 105711 READY: TSTB @R1 ; Done?		0x7756 105711 READY: TSTB @R1 ; Done?

Jnc: /* Bootstrap Loader format */ correc detail

2019-08-20T14:50:45Z

Bootstrap Loader format: correc detail

← Older revision		Revision as of 14:50, 20 August 2019
Line 40:		Line 40:
	* Load offset (1 byte)		* Load offset (1 byte)
	* Program to be loaded (up to 0344 bytes)		* Program to be loaded (up to 0344 bytes)
	* Copy of boostrap loader (first 7 bytes)		* Copy of boostrap loader (first 6 bytes)
	* Branch ~~offset~~ (1 byte)		* Offset to branch (1 byte)
			* Branch modification (1 byte)

	==Others==		==Others==

Jnc: /* Program */ correct loc

2019-08-20T14:47:34Z

Program: correct loc

← Older revision		Revision as of 14:47, 20 August 2019
Line 11:		Line 11:
	The program starts with the pointer set to itself, so the blank leader at the start of the data for the bootstrap loader (originally contained on [[paper tape]]s) starts with a special leader code which causes this to be left un-changed.		The program starts with the pointer set to itself, so the blank leader at the start of the data for the bootstrap loader (originally contained on [[paper tape]]s) starts with a special leader code which causes this to be left un-changed.

	The buffer pointer is then modified to point it ~~immediately~~ before the bootrap loader in memory, so at the end of the load the newly loaded code then progressively overlays the first several [[instruction]]s of the bootstrap loader itself, finally patching the buffer pointer to point at the branch instruction, which is then modified to jump to the newly loaded code.		The buffer pointer is then modified to point it slightly before the bootrap loader in memory, so at the end of the load the newly loaded code then progressively overlays the first several [[instruction]]s of the bootstrap loader itself, finally patching the buffer pointer to point at the branch instruction, which is then modified to jump to the newly loaded code.

	===Code===		===Code===

	This is the actual bootstrap program:		This is the actual bootstrap program:
	LOAD = ~~0x400~~ ; Buffer address		LOAD = 0x7400 ; Buffer address
	~~0x744~~ 016701 BEGIN: MOV DEVICE, R1 ; Get Device CSR
	~~0x746~~ 000026		0x7744 016701 BEGIN: MOV DEVICE, R1 ; Get Device CSR
	~~0x750~~ 012702 LOOP: MOV (PC)+, R2 ; Get buffer offset		0x7746 000026
	~~0x752~~ 000352 OFFSET: 0352		0x7750 012702 LOOP: MOV (PC)+, R2 ; Get buffer offset
	~~0x754~~ 005211 INC @R1 ; Turn on reader		0x7752 000352 OFFSET: 0352
	~~0x756~~ 105711 READY: TSTB @R1 ; Done?		0x7754 005211 INC @R1 ; Turn on reader
	~~0x760~~ 100376 BPL READY		0x7756 105711 READY: TSTB @R1 ; Done?
	~~0x762~~ 116162 MOVB 2(R1), LOAD(R2) ; Transfer		0x7760 100376 BPL READY
	~~0x764~~ 000002		0x7762 116162 MOVB 2(R1), LOAD(R2) ; Transfer
	~~0x766 0x4000~~		0x7764 000002
	~~0x770~~ 005267 INC OFFSET ; Bump buffer offset		0x7766 0x7400
	~~0x772~~ 177756		0x7770 005267 INC OFFSET ; Bump buffer offset
	~~0x774~~ 000765 BR LOOP		0x7772 177756
	~~0x776~~ yyyyyy DEVICE: yyyyyy ; Input device CSR address		0x7774 000765 BR LOOP
			0x7776 yyyyyy DEVICE: yyyyyy ; Input device CSR address

	==Bootstrap Loader format==		==Bootstrap Loader format==

Jnc: /* Program */ add actual code

2019-08-20T01:12:31Z

Program: add actual code

@@ Line 5: / Line 5: @@
 The original bootstrap loader is [[self-modifying code]], since this allows a very short program. The program is not directly self-modifying; rather, the nature of its input is such that it modifies the bootstrap loader as it is read in. (Most bootstrap loader input files eventually restore the bootstrap loader to its original condition, allowing it to be re-used.)
-==Structure==
+==Program==
 The bootstrap loader contains two locations which are modified by reading the input: the first is a [[pointer]] to the [[buffer]] in which to place data being read in; the second is a [[branch]] back to the beginning of the data input [[loop]].
@@ Line 12: / Line 12: @@
 The buffer pointer is then modified to point it immediately before the bootrap loader in memory, so at the end of the load the newly loaded code then progressively overlays the first several [[instruction]]s of the bootstrap loader itself, finally patching the buffer pointer to point at the branch instruction, which is then modified to jump to the newly loaded code.
 ==Bootstrap Loader format==

Jnc: Mention LSI-11 ODT

2019-08-19T18:47:19Z

Mention LSI-11 ODT

← Older revision		Revision as of 18:47, 19 August 2019
Line 4:		Line 4:

	The original bootstrap loader is [[self-modifying code]], since this allows a very short program. The program is not directly self-modifying; rather, the nature of its input is such that it modifies the bootstrap loader as it is read in. (Most bootstrap loader input files eventually restore the bootstrap loader to its original condition, allowing it to be re-used.)		The original bootstrap loader is [[self-modifying code]], since this allows a very short program. The program is not directly self-modifying; rather, the nature of its input is such that it modifies the bootstrap loader as it is read in. (Most bootstrap loader input files eventually restore the bootstrap loader to its original condition, allowing it to be re-used.)

	Several PDP-11 bootstrap ROMs, e.g. the [[BM792 ROM\|BM792-YA]], BM792-YK and [[BM873 ROM]] are prepared to read programs in bootstrap loader format. The code in them is obviously not self-modifying, but reacts to the bootstrap loader input format to produce the same effects.

	==Structure==		==Structure==
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	* Copy of boostrap loader (first 7 bytes)		* Copy of boostrap loader (first 7 bytes)
	* Branch offset (1 byte)		* Branch offset (1 byte)

			==Others==

			Several PDP-11 bootstrap ROMs, e.g. the [[BM792 ROM\|BM792-YA]], BM792-YK and [[BM873 ROM]] are prepared to read programs in bootstrap loader format. The code in them is obviously not self-modifying, but reacts to the bootstrap loader input format to produce the same effects.

			[[QBUS CPU ODT‎\|ODT]] in the [[LSI-11 CPUs]] also has a command to load programs in bootstrap loader format.

	==Further reading==		==Further reading==