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Inter-Office Memorandum
To Dorado project Date April 21, 1980
From Ed Taft Location PARC/CSL
Subject Dorado booting-operation and mechanisms File [Ivy]
XEROX
Dorado bootstrapping is a complex process, involving a number of hardware, microcode, and
software components. This memo attempts to document the booting mechanism thoroughly: how to
use it, how it works, and how the components are constructed and maintained.
Most Dorado users will be interested only in section 1. The other sections describe arcane
mechanisms and procedures that are of concern only to Dorado microprogrammers and maintainers.
1. Operation
Booting a Dorado from scratch involves two main activities: loading its control store with the correct
microcode, and then forcing it to load and run the correct software. At present, the second step uses
exactly the same mechanisms as are used on the Alto for bootstrapping software from the disk or
Ethernet. The descriptions here concentrate on the first step.
Emulators
The Dorado is able to execute programs written in a particular language (Mesa, Lisp, Smalltalk, or
Alto BCPL) by virtue of running emulator microcode-that is, microcode for emulating that
language. In addition, there is some common I/O microcode for controlling the I/O devices
(display, disk, Ethernet, etc.) This microcode is not built into the Dorado but rather must be loaded
into its control store from some external source.
The Dorado's control store is not large enough to hold the emulator microcode for all languages
simultaneously. Therefore, the microcode is divided up into several independent microprograms,
only one of which is used at a time. Each microprogram contains the Alto emulator and I/O
microcode, ana additionally contains the emulator for one other language. That is, the "Mesa
microcode" consists of the Alto emulator, the 110 microcode, and the microcode for emulating the
Mesa language; similarly for the "Lisp microcode" and the "Smalltalk microcode". (There is also
"Cedar microcode", which is presently the same as Mesa but will probably become different in the
future.)
Microcode booting
When the Dorado is first turned on, it automatically goes through a complete bootstrap sequence
that takes about a minute. (Most of this time is spent waiting for the disk to become ready.) If all
goes well, at tlle end of this time tlle Mesa microcode is loaded and the Alto Operating System on
disk partition 1 is started. This full bootstrap sequence can also be initiated by pressing the white
button on the front panel of the Dorado (inside tl1e cabinet, if the Dorado is cabinet-mounted).
Dorado booting-operation and mechanisms 2
Other forms of booting are initiated by pressing the boot button on the back of the keyboard, as
detailed in the following paragraphs. There are single- and multiple-push boots. Due to software
limitations, you must push the boot button for at least 0.25 second and no more than 2.5 seconds;
multiple pushes must be spaced no more than 1.5 seconds apart; and the bootstrap operation does
not commence until 1.5 seconds after you release the button for the last time.
I-push boot. This causes the currently-running microcode to go through the software
bootstrap sequence, i.e., loading th.e Alto as, or the NetExec if you have the BS and Quote
keys pressed down, or whatever. A l-push boot is the nearest equivalent to pressing the
boot button on an Alto. It works only if the correct emulator microcode is already loaded
and the Dorado is still running normally.
2-push hoot. . This causes the currently-running microcode to be forcibly restarted. It is
similar to a l-push boot, but it will work even if the Dorado has halted, and it does more
extensive microcode initialization (in particular, it zeroes main memory, and it reverts to
the default disk partition for the current emulator.) This does require, however, that there
be intact emulator microcode in the Dorado's control store.
3-push boot. This initiates the complete microcode bootstrap sequence, similar to the
automatic. power-on boot. This is the normal way to switch from one emulator to another
(see below). It assumes nothing about the current state of the machine.
4-push boot. This isn't really a boot: it causes the Dorado to shut down, a process that
takes about 30 seconds. Shutting down the machine is necessary, for example, in order to
change disk packs. When the machine is in the shut down state, pushing the boot button
(one or more times) will initiate a complete microcode bootstrap, similar to a power-on or
3-push boot.
If you have no keys pressed down during a power-on boot or a 3-push boot, you always get the
Mesa emulator. You may bootstrap other emulators by holding a key down during the boot:
C for Cedar
L for Lisp
M for Mesa (same as all-keys-up boot)
S for Smalltalk
For correct operation, you must hold the key down for at least 10 seconds after you initiate a 3-push
boot.
These keys are independent of the ones used to select the desired software to run. The latter keys
are the same as on the Alto; that is, to run the NetExec, you hold down the BS and Quote keys
while booting. Thus, to bootstrap the Smalltalk microcode and then run the NetExec, you might
have to hold down S, BS, and Quote and initiate a 3-push boot. Since this would require you to
have at least three hands, some more convenient (though less mnemonic) alternate keys are defined
for selecting the microcode to bootstrap:
= for Cedar
for Lisp
REfURN for Mesa (same as all-keys-up boot)
SHIFf for Smalltalk
Microcode self-loading
The Dorado can also load its own microcode under program control, using a special instruction
(LoadRam) described in section 2. There exists a program called LoadMB that runs on the Dorado
and loads emulator microcode from a file on the Dorado's disk. The file must be in MB (micro
binary) format, as produced by MicroD, and the microcode contained within that file must conform
to certain conventions in order to be soft-bootable in this manner.
Dorado booting-operation and mechanisms 3
For example, the Mesa microcode is contained in a file called Mesa.MB. To load and start that
microcode, type:
>LoadMB Mesa.MB
This loads the Dorado's control store with the contents of Mesa.MB and then starts it. That
microcode (since it is a standard emulator) in turn loads and starts the Alto OS from disk partition
1, the default partition for Mesa.
This means of loading microcode isn't very interesting for bootstrapping the standard emulators,
since the 3-push boot is easier and doesn't require the new microcode to be on your Dorado's disk.
But it is useful for loading non-standard or experimental emulators. (The LoadMB program has
some other features, described in section 3. The program is stored as [Ivy]
Loading microcode using Midas
Each cluster of Dorados has an umbilical Alto that is able to control a connected Dorado for
purposes such as hardware checkout and microcode debugging. The Alto program that performs
these functions is called Midas.
Most Dorado users will have no occasion to use Midas. But if the normal microcode bootstrap
mechanisms don't seem to be working, you can use Midas to load your desired emulator microcode.
If Midas is not already running, boot the Alto and type:
>Midas
Midas first displays a menu of the serial numbers of all the Dorados that are connected to this Alto.
Select your Dorado by positioning the cursor over your Dorado's serial number and clicking RED
(left or top mouse button). This step is skipped automatically if there is only one Dorado connected
to the Alto.
If the selected Dorado is running, Midas displays a status of "Running" and puts up a menu (near
the bottom of the screen) consisting of ABORT and DTACH items only. To halt the Dorado, select
ABORT.
Now Midas displays a large menu near the bottom of the screen. Select RUN-PROGRAM, and the
menu changes to a list of microprograms that you can run; these include CEDAR, LISP, MESA, and
SMALLTALK. Select one of those. The screen then goes blank while Midas loads the Dorado's
control store, a process that takes about a minute. After that, Midas starts the Dorado as if you had
initiated a 2-push boot.
Important: Do not leave Midas running on the Alto after you have loaded your microcode, because 2-,
3-, and 4-push boots from the Dorado's keyboard don't work if Midas is controlling the Dorado.
Therefore, exit Midas using SHIFT-SWAT (hold down the left SHIFT key and press the SWAT key,
which is the blank key to the right of right SHIFT).
The versions of emulator microcode stored on the Midas Alto's disk might not always be up-to-date.
If you are in doubt, update the microcode files by issuing the Executive command:
)@UpdateEmulators
which runs FTP to retrieve the current versions of all emulator microcode.
Dorado booting-operation and mechanisms 4
Machine status
There is a green light on the front panel of the Dorado that indicates the machine's present state, as
follows:
1 flash. Bootstrap sequence in progress (power-on or 3-push boot).
2 flashes. Bootstrap sequence failed.
3 flashes. Transient power-supply problem-voltage or current was out-of-spec at least
once since the last boot.
4 flashes. Present power-supply problem.
S flashes. Dorado has been shut down by 4-push boot
6 flashes. Dorado has overheated and shut itself down automatically.
7 flashes. Midas has taken over control of the Dorado.
Continuously on. Bootstrap sequence is believed to have completed successfully, and there
have been no occurrences of problems indicated by 3 through 7 flashes.
Continuously off. Unknown but probably serious malfunction, or AC power turned off.
2. How it works
The Dorado contains a microcomputer that performs several functions, including monitoring power
and temperature, turning on and off the main power supplies and the disk driv~, and initiating
bootstrap sequences. The microcomputer can sense the state of the boot button, and it controls the
green light. This microcomputer and attendant EProms and other logic are mounted on the
BaseBoard, the bottom logic board in the machine.
A I-push boot is handled entirely by the Dorado microcode itself, with no action by the BaseBoard.
Multiple-push and power-on boots are handled by the BaseBoard. A 3-push or power-on boot
involves the following multiple-step sequence.
Loading Bootstrap microcode
The BaseBoard first halts the Dorado, issues an 1/0 reset, and resets or disables conditions that
could interfere with initial bootstrapping (Hold, Fault task wakeup). It then forcibly loads into the
Dorado's control store a small (-50 instruction) microprogram called Bootstrap. Finally, it starts the
Dorado executing this microprogram.
Loading of Dorado microcode in this manner is very slow; therefore, the amount of microcode in
Bootstrap is kept as small as possible.
Loading Initial microcode
Next, the Bootstrap microprogram and the BaseBoard microcomputer cooperate to load into the
Dorado's control store a somewhat larger (-700 instruction) microprogram called Initial. Initial is
stored as data in the BaseBoard's EProm. It is read by the microcomputer and handed to the
Dorado (via CPReg) at relatively high speed; the Boostrap microprogram copies this data into the
Dorado's control store.
When this operation is finished, the Boostrap microprogram gives control to the Initial
microprogram it has loaded. Bootstrap and Initial are arranged to occupy disjoint regions of the
control store. The BaseBoard then waits for the Dorado to complete the next step.
Dorado booting-operation and mechanisms 5
Initial execution
Initial performs a number of operations. First, it does a more thorough initialization of the Dorado.
It corrects parity in all registers and memories. It initializes the memory system (cache, map, and
storage) and puts it into a usable state. Finally, it notifies the BaseBoard that this step has been
completed successfully. (This notificatioJ:?, causes the BaseBoard to tum the green light continuously
on. If this event fails to occur within a reasonable time, the BaseBoard switches to the 2-flash
indication.)
Second, Initial enables the I/O tasks that it requires (Display, Ethernet, and Junk tasks). It then
reads the keyboard in order to determine which emulator microcode to bootstrap.
Third, Initial makes contact with an Ethernet boot server (located in a Gateway or IFS system) and
requests it to supply the selected emulator microcode. That microcode is transferred over the
Ethernet and stored in the Dorado's main memory. (This step employs the Pup Microcode Boot
protocol, which is also used for booting DOs and is documented in [Maxc]Finally, Initial calls the LoadRam procedure, which loads the emulator microcode from main
memory into the Dorado's control store (1M and IFUM) and transfers control to its starting address.
The emulator microcode replaces Bootstrap and Initial. LoadRam is a standard one-page microcode
loading routine which is included in Initial and in every emulator. It occupies the same region of
control store in each microprogram. Therefore, LoadRam can load a new microprogram without
danger of overwriting itself.
Software bootstrap
When the emulator microcode is started-either as a result of the above sequence or by a 2-push
boot-it does some further memory system initialization, including zeroing out all main storage. It
resets the disk partition to the default one for that emulator. It initializes all I/O devices. Finally, it
initiates an Alto-style software boot from either disk or Ethernet, according to the keys that' are
pressed down.
A I-push boot is detected and handled by the emulator microcode itself, without action by the
BaseBoard. It performs all actions described in the preceding paragraph except for zeroing memory
and resetting the default disk partition.
The Alto-style software boot is described in Alto documentation: the Alto Hardware manual
([Maxc]