This page describes the basic usage of the Hades simulator applet.

System requirements and browser setup:

• system requirements and setup
• download time
• configuration
• security

General information and user-interface:

• user-interface overview
• using the popup-menu
• bindkeys
• contolling the simulation
• logic model and glow-mode colors
• interactive switches
• editing and parameters

Additional and further documentation:

• troubleshooting
• documentation and links

System requirements and setup

Java JDK/JRE 1.4.2 or higher

Java webstart

Memory limit

If the Java plugin runs out of memory, the applets will react very slowly to user input, and the simulation might show bugs due to internal out-of-memory errors. In this case, you will have to exit and restart your browser, because there is currently no way to re-initialize the Java plugin or to increase the amount of memory at runtime.

Therefore, it is recommended to specify a larger amount of memory before running the applets. Open the Java plugin control panel and select a larger maximum amount of memory via the user-interface or runtime switches. For example, add the -Xmx256M runtime flag to specify an upper limit of 256 MBytes (instead of 64 MBytes). You may have to restart your browser after changing the Java plugin runtime parameters.

The details depend on your operating system and Java version; please check your system documentation or ask your local Java guru for help. In the original JDK/JRE from Sun Microsystems, the Java plugin control panel application is located at $JDKDIR/jre/bin/ControlPanel(.exe). The image below shows a screenshot of the control panel with the -Xmx extra runtime argument on a Linux system. On Windows, you can start the Java plugin control panel either directly from the Java runtime environment installation directory, or via the Windows software configuration utility (start-menu/settings/software, scroll down to locate the Java plugin entry.)

Download time and problems

The downside, however, is that you also need some patience, because downloading the software will take a while, especially on slow (analog modem) dialup lines. Once loaded, the applet software files will be cached by your browser, so that re-opening the web-page with the applet or opening another web-page that uses the same applet code will be much faster. For the Hades applet demos, loading the first applet will be quite slow, but opening another webpage should take a few seconds at most.

Unfortunately, the security mechanisms of Java enforce that your browser will not start a Java applet until it has downloaded the complete applet software. If the applet is digitally signed, the browser will also check those signatures before trying to run the applet code.

If the webmaster chooses to use the standard Hades software archive (called hades.jar), only a single file needs to be downloaded by your browser. At the moment, the hades.jar archive file takes about 5 MBytes, which amounts to download times of a few seconds on a fast intranet, about a minute via a DSL (1024 kbps) modem, but can take twenty minutes via a standard analog modem (40 kbps) line.

To reduce the download and startup times, the webmaster might also decide to partition the Hades software archives. This makes sense, because most applets reference and use only a small subset of all simulation models contained in the complete hades.jar software archive file. However, the setup and maintainance of this type of installation is pretty difficult, as every interdependence between applets has to be checked. For this setup, the gate-level circuits applets require only the basic software archive, hades-applet.jar of about 2 MBytes. This implies a download time of about two seconds on T1 lines, a few seconds on DSL, and still about 8 minutes on an analog modem line. Also, note that you may expericence another startup delay as soon as you access an applet that requires to download one of the extra partial software archive files, like hades-models-rtlib.jar (about 400 KBytes) or hades-models-imaging.jar (about 180 KBytes).

At the moment, we are not quite sure whether the monolithic-big-applet-archive approach or the multiple-smaller-applet-archives approach is better. The former incurs a possibly very long startup time at the first download, but no additional download times are required afterwards; also, the single applet archive is easier to maintain. The latter means that the basic applets start faster, but additional download pauses are required when browsing through the applet collection. Please provide your feedback and ideas about this problem!

Applet configuration

A webdesigner can specify a second configuration file via the applet-parameter Hades.Applet.Hadesrc, whose name is resolved relative to the current applet codebase. This allows setting the attributes for individual applets without the need to change the hades.jar archive.

After reading those global configuration files, the Hades editor attempts to read the user and local configuration files, which allows you to customize the simulator to your personal perferences. While the Hades applet will also try to read these files, the default security settings deny all file access to Java applets, which means that reading your local configuration files will fail.

Applet security and .java.policy

However, the security mechanism used by Java allows you to specify exactly what operations are to be permitted for each application and applet, based on the original codebase (webserver URL). To allow the Hades applets to read files on your local computer, you will have to edit the global Java security configuration file, called .java.policy in your home directory.

Please check your Java documentation for details about creating and editing the policy file via the policytool program. Unfortunately, that program is rather user-unfriedly and difficult to use. Therefore, we offer a small utility to help you create a java.policy file with the settings required to run Hades with full functionality as an applet. Please click the following link for details about our Java Policy Editor.

Finally, it is also possible to just edit the policy file with your favorite text editor; just make sure not to introduce any syntax errors. The following .java.policy file provides an example of the settings required. It allows the Hades applet to read the configuration files when loaded from our webserver. Note that you will have to restart your browser after changing your .java.policy file for the settings to take effect.

(While our sample configuration file also includes an example (commented out) of the AllPermission setting, this should only be used during applet development or when all else fails. Visiting an unknown website with the AllPermission setting in effect is not a good idea.)

User-interface overview

Please check the applet welcome page and user-interface overview for an introduction and interactive demonstration(s) of the Hades applet. Follow the "next" links on the pages to learn about the the basic concepts of the Hades user-interface.

Fixed applet size, or external window

For best compatibility with the standard screen resolutions found on current LCD monitors and projectors (800x600 and 1024x768 pixels), all applet webpages contain relatively small applets at 700x500 pixels. This allows to display the navigation menu on the left together with the applet and the first few lines of circuit description on the screen. The zoom factor of the editor is then calculated so that the circuit schematics into the applet. This works well for most of the simple circuits, but may result in pretty small zoom factors for some of the more complex circuits.

If necessary, select the open in external window popup-menu item to open a new external window and to display the circuit schematics in this window. You can then resize the window to fit your screen. When you next select the open in external window function, the applet should remember the window size and position selected previously. Click the window-close button to close the external window and return to the inline applet embedded into the webpage.  

Popup-Menu

Bindkeys

Note that the behaviour of the Hades editor depends on whether view-mode is selected or not. When view-mode is active, the editor first checks whether some input component (switch, power-on-reset, clock-generator, etc.) is registered for a keystroke. If such component is found, the keystroke is used to control the component, which is much easier and faster than moving the mouse around to click on the component. If the tooltips to be used to control simulation components are not indicated in the schematics or corresponding documentation, just enable tooltips (via the popup-menu) and rest the mouse cursor a few seconds over a component. The tooltip window indicates the shortcut key for that component.

Often, the 'c' and 'r' keys will be used for clock and reset signals, while '0', '1', '2 ', etc. are used as data inputs. If no clock signal is required, 'a', 'b', 'c', etc. will also be used as data inputs. For standard input components (Ipin), typing the bindkey will toggle the output between the values StdLogic1164.0 (low) and StdLogic1164.1 (high), while typing shift+bindkey will toggle the output value between 0 (low), 1 (high), Z (tri-state), and X (undefined).

If view-mode is deselected, the editor will bind many simple keystrokes to edit commands, e.g. 'm' for move component or 'c' for copy component etc. Please check the Hades tutorial and Hades help menu for documentation about the complete set of editor bindkeys.

In both view-mode and edit-mode, the Hades editor and applet also accept several of the common keyboard shortcuts, when used together with the control-key as a modifier.

• control-O open design file
• control-N start new design
• control-Q quit editor, close external applet window
• control-P print (may be disabled for applets)

• control-C copy to clipboard (still disabled)
• control-X cut to clipboard (still disabled)
• control-V paste from clipboard (still disabled)

• control-R redraw
• control-F zoom fit
• control-G toggle glow-mode
• control-H toggle grid-mode
• control-J toggle layers

Additionally, the Hades applet supports the following bindkeys, unless those keys are used to control input switches in the current schematics:

• f - zoom-fit
• z - zoom-out
• Z - (shift+z) zoom-in
• e - edit component parameters (show property sheet for a simulation model)
• g - toggle glow-mode on and off

• p - add probe (waveform trace) to signal
• P - remove probe (waveform trace) from signal

Simulation control

• Use the drop-down list control on the left to select the simulation algorithm to be used. For most of the interactive demonstrations, the VHDL simulation mode should be used.

• Click the info button to print a short summary of the current simulation state to the standard output. To see the output, you have to enable and open the Java console in your browser.
• Click the rewind button to stop the simulation.
• Click the pause button to interrupt the simulation; you can resume simulation by clicking the Fast-Forward button.
• Click the run (Fast-Forward) button to start a new simulation or to resume a paused simulation.
• Click the run-for-interval button to run the simulation for the amount of time selected via the interval textfield and time units drop-down list. Once the selected time has elapsed, the simulator will switch to the paused state and wait for another command.

• The traffic light control indicates the current simulator state: red for stopped, yellow for paused, and green for running.
• The time panel indicates the current internal simulation time. In the default, real-time VHDL simulation mode, the simulation time will agree with the actual runtime (if the simulation runs fast enough).

Logic model and glow-mode colors

Most gate-level simulation models in Hades use a nine-valued logic model based on the industry-standard system called 'std_logic_1164'. For details, please see the logic values and glow-mode colors demonstration page. The main idea is to provide additional logic values besides the standard values '0' (low voltage) and '1' (high voltage), so that the simulation can distinguish other important situations like 'X' (unknown value) or 'Z' (tri-state, not-driven).

The actual mapping from logical value to colors depends on the signal type and the settings in your Hades configuration files. In the default configuration of the applets, the following colors are used for the five most important states:

The use of the rather 'aggressive' colors cyan and magenta for the 'U' and 'X' values makes it very easy to spot problems (like unconnected or short-circuited signals) during the simulation.

Switches

There are several variants of interactive switches. Please check the interactive switches demos for further information:

• Ipin  click to toggle between the 0/1 values, or use shift+click to toggle between 0/1/Z/X.
• IpinLarge  same as Ipin, but with a larger symbols (easier to see and click at small zoom-factors)
• PulseSwitch  click to generate a short 0-1-0 pulse; the actual pulse duration can be selected via the property sheet.
• PowerOnReset  click to toggle between the 0/1 values. Automatically generates a U-0-1 pulse suitable for (active-low) reset of settable duration at simulation startup.
• ClockGen  click to disable or enable the clock signal. Timing parameters like frequency can be selected via the property sheet.
• IpinVector  provides an n-bit output value; use click and shift+click to increase or decrease the output value.

Troubleshooting

Slow startup:

Deadlocks:

Please provide detailed feedback (applet, operating system, browser, Java virtual machine, ...) when you experience such problems in order to help debugging.

Keyboard focus problems:

A frequent problem is that the applets do not react to keyboard input at all, because the browser does not give them the so-called keyboard focus: in other works, the browser does not propagate keyboard events to the applets. For example, on my Linux system with Mozilla (1.7.7), this seems to happen when the applets are not completely visible due to a small browser window size. Naturally, due to the large number of operating-system/browser/JavaVM combinations, many different behaviours are possible. Try the following actions to restore the keyboard focus to the applet:

• Please try a mouse-click into the main applet schematics viewer, so that the applet requests the keyboard focus from the browser, then try the typing the bindkey again.
• Try to activate the popup-menu of the applet, then release the popup-menu, and type the bindkey again.
• Try to resize the browser window and click in the applet to restore the keyboard focus.

User-interface getting slow

Memory usage (out of memory errors)

Further documentation

• Hades applet FAQ
• Hades tutorial (PDF, English)
• Hades Kurzreferenz (PDF, German)
• Hades homepage