pkimpel.retro-b5500/WebUIUsingTheConsole.md

WebUI Using the B5500 Console

Compared to virtually every other computer system of the 1960s, the Burroughs B5500 had an extraordinarily minimalist operator console -- just five buttons and six lights, plus a few more on the Teletype SPO (supervisory printer/keyboard). The best image we have of the Console is from the 1968 Burroughs Corporation annual report:

That image shows the B5500 at the City of Montreal, Canada. In the foreground is the L-shaped console desk, with the Teletype Model 33 SPO. You can see part of a card reader behind the SPO and magnetic tape drives in the background.

We have tried to be faithful to the design of the Console in our representation of it for the web-based user interface:

There were lots more lights, buttons, and switches on the maintenance panels in the Display and Distribution (D&D) Unit, but those were intended for use in maintenance and diagnosing hardware problems, not operating the system. They were usually behind the D&D cabinet door, out of sight, and thanks to an interlock switch on the door, powered off.

The Console is the central control for the web-based emulator. To display the Console, navigate to the emulator's home page, B5500Console.html in the webUI/ directory of emulator files on your web server. If you are running the emulator from our hosting site, simply go to

http://www.phkimpel.us/B5500/webUI/B5500Console.html

The home page will look similar to this:

On the home page, click one of the "Start" buttons. This will open a small window for the Console.

• The Start & Power On button will open the Console window and automatically power up the emulator, as if you had clicked the Console's green POWER ON button.
• The Start - Powered Off button will simply open the Console window without powering up the emulator. You may wish to use this button if you want to make configuration changes before running the emulator, as such changes can be made only when the emulator is in a powered-off state.

Once the Console window is open, you may move it around on your screen, or even minimize it. Closing the Console window will implicitly halt the system and power down the emulator. The emulator will display a warning dialog if you attempt to close the Console window while the emulator is powered up.

Layout of the Console

The Console is used to power the system on and off, initiate a load (boot) of the operating system, and halt the system. The A/B Normal/Control lights give a basic indication of system activity. All other operations are handled through the SPO.

From left to right, the controls on the Console are:

• HALT button -- clicking this red pushbutton halts the system. This initiates an immediate termination of all processing. The only way to continue after halting is to click LOAD and reboot the system. The button illuminates when power is on and the system is halted.
• NOT READY light -- this white indicator illuminates when one of the components of the system that did not have its own ready/not ready indicator is in a not-ready or off-line state. It applies to processors, I/O units, memory modules, and the first drum (if present). The emulator handles this in a similar manner. It will turn on the light if, at the time the system is powered on, any of the following conditions are true, as they will prevent the system either from booting or from supporting the MCP:
  • No Processor is enabled in the current configuration.
  • One of the enabled processors is not designated as P1, the control processor.
  • No I/O Control Units (channels) are enabled.
  • Memory module 0 (having addressees 00000-07777 octal) is not enabled.
  • The SPO device is not enabled in the configuration.
  • The DKA device (Disk File Control A) is not enabled in the configuration.
• MEMORY CHECK -- this red light illuminates when a memory parity error is detected by either processor. The emulator does not presently generate memory parity errors, however. Clicking this light while power is on will produce a full dump of processor state and memory in a separate browser window. This dump can be generated at any time, even while the system is running.
• LOAD -- clicking this black pushbutton clears all registers in the system and initiates a load operation. When loading from disk, 63 sectors (1890 words) are read into memory starting at location 20 octal. When loading from cards, one binary card is read starting at location 20 octal. If the read is successful, Processor 1 then starts executing at that address.
• CARD LOAD SELECT -- this yellow button/light controls whether a load operation reads from the first disk¹ or the first card reader. In its normal position, load is from disk. When pressed, the physical button latched inward and illuminated, enabling load from cards. In the web-based emulator, the state of the button toggles each time you click it, but the button only illuminates.
• A NORMAL -- this yellow light illuminates when Processor A is operating in Normal State (i.e., running user code).
• A CONTROL -- this yellow light illuminates when Processor A is operating in Control State (i.e., running MCP code).²
• B NORMAL -- this yellow light illuminates when Processor B is operating in Normal State.
• B CONTROL -- this yellow light illuminates when Processor B is operating in Control State.
• POWER ON -- clicking this green light/button initiates a power-up sequence for the system. The button is illuminated while power is applied to the system. In the web-based emulator, clicking this button first runs a brief lamp test. The emulator then loads the current configuration parameters, initializes the internal emulator components, and opens a series of sub-windows for the peripheral devices configured for the system -- SPO, card reader, line printer, etc.
• POWER OFF -- clicking this black pushbutton initiates a power shutdown sequence for the system. In the web-based emulator, clicking this button halts the processor(s) and closes the peripheral sub-windows.

When the Console window first opens, only the POWER ON button is activated. Once power is applied and the emulator is initialized, the POWER OFF and LOAD buttons become active and POWER ON is disabled. Once LOAD is clicked, HALT becomes active and LOAD is deactivated. When power is on, POWER OFF can be clicked at any time, even while the system is running programs.

When the SPO window opens, it will print a short message indicating the emulator version. Please wait for this message to finish printing before attempting to click the LOAD button. The LOAD button will not function until the SPO is on line and goes to REMOTE status.

Once you load the system, there is generally nothing further you need to do with the Console -- except watch the pretty lights -- until you are ready to halt the system. The SPO window will probably be the one you use the most.

The emulator, like the B5500, is fairly robust. You can halt or power off the system at any time. You can even just quit the browser. We recommend, however that you do an orderly shutdown when you are finished with the system -- click HALT, then POWER OFF, then close the Console window, and then quit the browser if desired.

To reboot a running system, click HALT and then LOAD. You may halt the system and power it off, then power it back on and do a load without quitting the browser. In order to change the emulator configuration, you must halt and power down the emulator.

You may move and resize the emulator windows in any way you wish, including the Console window. You may also minimize any of the windows, but do not close the peripheral windows. Closing one of those will render that device inoperable until the emulator is reinitialized with the POWER ON button. Closing the emulator window will abort the emulator.

Some web browsers, particularly Firefox, slow the execution of Javascript scripts while they run in a non-active tab of a window. The emulator has a performance throttling mechanism that attempts to run the B5500 processor at its real speed. To keep this mechanism from falling behind in terms of real time, avoid opening the B5500 Console in a window with multiple tabs where one of the other tabs is the active one. It is best to open the Console in its own window, or at least keep it as the active tab in a window. If you need to use the browser to access other web sites at the same time the emulator is running, we recommend that you open separate browser windows to do so.

See the Running the Emulator page for more information on using the Console to start the emulator and operate it.

Emulator Features Added to the Console

Since the emulator is not a physical system, it is often difficult to tell exactly what is happening while it runs. To give a better view of what is happening within the system (and just because it was sort of a cool thing to do), the emulator displays a series of white annunciator lights in two rows below the standard buttons and lights. If you are a purist and don't want to see these additional lights, you can toggle their display off and on by clicking the Burroughs logo in the upper-right corner of the Console.

Clicking the retro-B5500 logo (or the plain B5500 logo if the Console is in purist mode) while the emulator power is off will open a sub-window from which you can examine and alter the system configuration. Processors, I/O Units, memory modules, peripheral devices, and a disk subsystem can be included or excluded from the configuration. Multiple, named configurations can be stored and recalled, so you can easily maintain different configurations for different purposes. You can also maintain multiple disk subsystems and switch among them. See Configuring the System for details.

In non-purist mode, the Console displays the names of the current system configuration and current disk subsystem above the Burroughs logo. It also displays the current version of the emulator below the Burroughs logo and to the left of the retro-B5500 logo.

The MEMORY CHECK indicator was a lamp and not a pushbutton on the B5500. If you click this lamp while the emulator is in a powered-on state, however, the Console will generate a full dump of processor and core memory state in a separate window. You may then save the contents of this window to a file or copy/paste it into another program for analysis. Simply close the window when you are finished with it.

Note: Prior to release 1.00, clicking the NOT READY indicator allowed you to toggle Processor B into and out of the current system configuration. With the implementation of the interface for system configuration in that release, however, this behavior has been removed. The number of processors in the system is now controlled through the configuration interface.

The Console attempts to update its display every 50 milliseconds. This update period applies not only to the annunciators below, but also to the A/B Normal/Control lights described above. Generally, an annunciator is illuminated if the corresponding element of the system had any activity since the last update of the display. The A/B Normal/Control lights use multiple shades of yellow to simulate lamp intensity, which in turn indicates the relative amount of time a processor is in each state.

The top row of annunciators displays activity for the I/O Units (channels), external interrupts, and Processor 2 control for the system:

• IOU1 -- I/O unit 1 busy (i.e., an I/O is active on this unit)
• IOU2 -- I/O unit 2 busy
• IOU3 -- I/O unit 3 busy
• IOU4 -- I/O unit 4 busy
• TIMR -- Interval timer interrupt (fires every 1.067 [64/60] second)
• IOBZ -- I/O busy interrupt (i.e., no I/O unit available)
• KBD -- Keyboard request interrupt
• PR1F -- Printer 1 finished interrupt
• PR2F -- Printer 2 finished interrupt
• IO1F -- I/O unit 1 finished interrupt
• IO2F -- I/O unit 2 finished interrupt
• IO3F -- I/O unit 3 finished interrupt
• IO4F -- I/O unit 4 finished interrupt
• P2BZ -- Processor 2 busy interrupt
• INQ -- Remote inquiry request interrupt
• SPEC -- Special interrupt #1 (not used)
• DK1F -- Disk file control #1 read check finished
• DK2F -- Disk file control #2 read check finished
• P2BF -- Processor 2 busy flip-flop³
• HP2F -- Halt Processor 2 flip-flop

The second row of annunciators displays activity for the peripheral devices in the system:

• DRA -- Drum #1
• DRB -- Drum #2
• DKA -- Head-per-Track disk control #1
• DKB -- Head-per-Track disk control #2
• SPO -- Supervisory keyboard/printer
• CPA -- Card punch
• CRA -- Card reader #1
• CRB -- Card reader #2
• LPA -- Line Printer #1
• LPB -- Line Printer #2
• DCA -- Data Communications Adapter
• PRA -- Paper tape reader #1
• PRB -- Paper tape reader #2
• PPA -- Paper tape punch #1
• PPB -- Paper tape punch #2
• MTA-MTT Magnetic tape units 1-16 (letters G, I, O, and Q are not used)

At the far right of the lower portion of the Console are two statistics that indicate how well the emulator for Processor 1 is performing:

• P1 Slack: the exponential moving average for the percentage of time the emulated processor is delaying its execution in order to throttle its performance to that of a real B5500. Numbers closer to 100% indicate the processor emulation is using relatively small amounts of your workstation's physical processor. Numbers closer to zero indicate the emulator is unable to run at the speed of a real B5500.
• P1 Delay: the exponential moving average amount of time (in milliseconds) that processor emulation is delayed during throttling, in excess of the amount of time it requested to be delayed. This is somewhat an indication of how precise the Javascript setTimeout() mechanism is in your browser. This value may fluctuate in response to the intensity of the instruction stream, I/O activity, browser overhead (e.g., memory garbage collection), or interference from other programs running on your workstation. If this value continuously increases, however, it means that your workstation is unable to run the emulator at the speed of a B5500.

In our experience with Mozilla Firefox and Google Chrome, the delay number is typically about half the browser's actual precision, plus one or two milliseconds. HTLM5 standards specify that browsers must have a precision of at least four milliseconds, so you should see values in the 3-4ms range for a compliant browser. Lower values are better, as all of the emulation takes place on one Javascript thread, and shorter delays allow the emulation to switch among processor and I/O tasks more efficiently.

Note that on most Windows systems, at least through Windows 7, the default timer precision is about 15ms, and you typically should see average delays in the 7-8ms range. Google Chrome is known to mess with the Windows timer mechanism beneficially, however, and meets the HTML5 requirement. Curiously, Chrome's effect on the Windows timer is system-wide -- if you run the emulator in Firefox at the same as Chrome is active in your workstation, the average delay in Firefox will be about the same as it is for Chrome. Starting with version 23, Firefox under Windows appears to handle timers more precisely as well.

Beginning with emulator version 0.20, we are using the Javascript performance.now() API to measure time more accurately, but that does not affect the precision of the Javascript setTimeout() function.

Operating the Emulator Off-line

Starting with release 1.00, the emulator supports an HTML5 feature known as the "Application Cache." This feature allows the emulator to be installed on your local workstation as a web application, and for it to function when your local workstation is not connected to a network, or is otherwise unable to contact the web server where the emulator is hosted.

Installation of the emulator files for off-line use is automatic. When operating your local workstation off line, you load the emulator into the browser exactly the same way as when on line, using a URL that addresses the webUI/B5500Console.html page at the server on which the emulator is hosted. The browser will recognize that it cannot contact the web server and will load the emulator files from its application cache. The rest of emulator operation is the same as when using it on line.

The first time you load a version of the emulator enabled for off-line use, the browser will automatically download the files and install them in its application cache. Thereafter, each time you load the emulator when the browser is on line to the web server, the browser will automatically check to see if a newer version of the emulator is available on the server. If a newer version is available, the browser will automatically download it in the background to the application cache. The new version will not be used, however, until the next time the emulator is loaded (or reloaded) in the browser.

When you load the emulator into your browser, the Console will display messages in its upper-left corner, above the HALT button, indicating progress of the browser checking for a newer version and downloading any updates. The last in the sequence of progress messages will remain on the Console for several seconds, and then will be erased. You do not need to wait for these progress messages to go away before powering-on the emulator or loading the MCP -- those activities can be initiated while the checking and downloading process is taking place.

You will see some combination of the following messages on the Console while it is checking and updating the application cache:

Checking for emulator update...	The browser has initiated the process of checking for a newer version of the emulator.
Emulator version is current.	The browser determined that no newer version is available.
Initiating download for emulator update...	The browser has determined that a later version of the emulator is available on the server and has initiated downloading the new files.
x of y resources downloaded thus far...	This message may appear occasionally during download of new files to indicate the progress of the download.
Emulator update completed. Reload this page to activate the new version.	Download of a new version completed successfully, but the browser is still using the former version of the emulator. The new version can be made available by powering-off the emulator and reloading the Console page.
Emulator is now installed for off-line use.	This message will appear the first time the emulator is downloaded and installed into the browser's application cache.
Unable to check for emulator update.	The browser is unable to contact the web server or access the emulator's manifest file. The emulator will run in the off-line mode.
Emulator off-line installation has been disabled.	The manifest file for the application cache has been removed from the server. This causes the emulator to be removed from the local application cache. Off-line operation of the emulator is no longer possible.

Note that in order to properly serve the manifest file that enables Application Cache functionality for the emulator, your web server may need to be configured to apply the MIME type "text/cache-manifest" to files with a ".appcache" extension on their file name.

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¹ On the B5000 and early B5500s, hardware load operated from sector 0 of the first drum device (DRA). Later B5500s were modified to load from sector 1 of the first Head-per-Track disk device (DKA). Systems wired to load from drum but without a drum device used a one-card bootstrap program to load the KERNEL bootstrap program from sector 1 of the disk, which in turn loaded the MCP. Such systems were thus effectively always booted from cards.

² The B5000 and B5500 could have two processors, which were physically identified as Processor A and Processor B. Both processors were identical, with their identification determined by where they were plugged into the D&D. Based on a manual switch in the Central Control Unit, one processor could be designed as Processor 1, the control processor. The other (if present) would then be Processor 2. Only Processor 1 could run in Control State, execute MCP code, and respond to interrupts. Processor 2, if present and enabled, could run only user programs in Normal State, and was essentially a slave to Processor 1.

³ P2BF serves primarily to inhibit P1 from initiating a program on P2, so it is always illuminated for a system where a second processor is disabled or not configured.