This page collects some of the frequently asked questions about Hades, and their answer. Please don't hesitate to contact us to add any relevant information that is missing here!

What is Hades?

• a simulation engine (actually several different simulators).
• an interactive graphical editor.
• tools for visualization (e.g. glow-mode).
• a library of simulation components (e.g. digital logic gates, flipflops, memories, microprocessors).
• a library and design browser.
• a waveform viewer to trace signals.
• a Jython scripting interface.

The name "Hades" stands for "Hamburg Design System", but also indicates that some of our computer science students don't really like having to learn about digital systems - Hades is meant to help them.

Where do I find information about Hades?

If you prefer printed documentation, download and read the Hades tutorial.

Which version of Hades do I have, which version do I need?

If you are running Hades as a standalone application, the version number will be displayed in the window title. Or select the "About" menu item in the "Help" menu to open a dialog window with version information. Select the "Changes" menu item to see a list of recent changes to Hades; you can also look at the hades/doc/CHANGES text file contained in your hades.jar archive with your favorite Zip-archive packer.

The applet won't start

For historical value, the following table summarizes our experiences of common browsers and Java virtual machines around 2007:

Also, please remember that your browser has to download the whole applet software before starting the applets. As the complete hades.jar archive file is about 5 MBytes, the downloading itself can take a while even on fast internet connections. A typical first-time startup time on a fast DSL modem lime (1000 kbps) is 20..30 seconds. Afterwards, the browser caches the applet software archive, and individual pages should load in a few seconds. See the usage page for details about download time and applet setup.

You will need quite some patience when trying to access the applet demos over a slow internet connection like an analog modem line: 5 MBytes at a typical rate of about 40 kbps (or 4 KB/s) implies an initial download time of about 1250 seconds (or 20 minutes). After that, most individual applets will load in a few (up to ten) seconds, but a few applets (e.g. the carry lookahead adders) are based on dozens of subcomponents with correspondingly longer download times.

The first applet worked, but the next applets won't

I just downloaded the Hades archive, but it won't run!

1. the hades.jar archive file with the Hades software,
2. a suitable Java virtual machine.

In theory, Hades should run with any Java 2 compatible Java virtual machine. When using the AWT-mode, the editor and many simulation components may even be used with an old Java 1.1-generation virtual machine, but such setup is no longer supported.

In practice, you should use JDK/JRE (Java development kit, Java runtime environment) version 1.4.2 or J2SE 5.0 (a.k.a. Java 1.5.0) or later. To run the editor, open a shell and type the following command:

  java -Xmx256M -jar hades.jar

Can I use the Java Runtime Environment (JRE) instead of the JDK?

Can I run Hades as an applet inside a WWW-Browser?

However, note that the applet version is mainly intended to allow easy access to pre-defined example circuits. As such, most edit functions are disabled in the applet version.

I cannot open files!

No sound!

If audio output does not work on your system, please check the following:

• when running the Hades applets inside your browser, please ensure that you granted the required AudioPermission, see the next paragraph.
• check that audio functions are enabled by your operating system.
• check volume controls and speaker/headphone cables.
• on Linux, stop all other programs that play audio (e.g. mp3 playback), then restart the Hades application or your browser (Hades applet). On many Linux systems, several incompatbile drivers (e.g. alsa/oss/artsd) are installed, and a running application will often access the sound device directly instead of accessing it via a mixer device. In such cases, other applications are denied access to the sound device.

The default configuration of the Java virtual machine denies applets any audio output, to prohibit malign applets from bothering the user. Therefore, you will have to add an explicit "AudioPermission" entry to your Java security control file (.java.policy) in order to get audio including the text-to-speech functions working. Please read the security information in the usage page for details about the Java security mechanism and the required entries in your .java.policy file. Or click the following link to directly go to our Java Policy Editor.

The applet worked, but the Webstart version don't

What are those funny colors?

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 simulation is slow!

On modern PCs or workstations with a recent Java virtual machine, the Hades simulator will usually run at about one million simulation events per second. (This isn't so much slower than some discrete-event based commercial simulators for digital circuits, e.g. some versions of Synopsys VSS. Note that Hades can do fewer optimizations and has to do many more runtime checks, because it allows editing and modifying the circuit as runtime.)

Also, Hades should be able to run at 10 ... 50 screen redraws (or frames/second) in interactive simulation. However, redrawing the screen often takes much more time than the simulation itself, especially when glow-mode is activated or the circuit contains many interactive components like LEDs.

I cannot print!

I hate those tooltips!

The applet crashed!

One failure scenario occurs when quickly browsing through the list of applets. Each time you visit a new applet page, the previous applet has to be stopped and destroyed by the Java virtual machine. However, in order to start the new applet as quickly as possible, all current Java plugins first start the new applet before they begin to clean-up the previous applet(s). If you request too many applets to quickly, the Java pluging doesn't manage to clean up at all, and runs out of resources. The details are highly system dependent, but the usual outcome is that the Java virtual machine starts to consume 100% of CPU time without doing any useful work. In some cases, you may even have to kill the Java virtual machine via the task manager (just restarting the browser won't always help in this situation, because the virtual machine is busy with itself).

Also, the Java plugin somehow seems to leak about 300 KBytes of memory per invocation of the Hades applet (at least on Unix/Linux systems.) This really should not happen, because all applet resources are claimed to be destroyed when you leave the applet webpage. While 300 KBytes doesn't sound much, the lost memory sums up pretty quickly when you visit a lot of applets. Remember that the default memory limit for the whole Java plugin is only 64 Mbytes. Browsing through all Hades demonstration applets alone might eat up all available memory, unless you increase the memory limit via the Java plugin control panel.