SimmStick Cyclone FPGA Board



Cyclone Board
Acex Board


This site is designated for a processor design to implement the Java Virtual Machine in hardware. It is part of a PhD thesis at the Vienna University of Technology, Austria. The goal of this development is a simple and small Java processor optimized to execute Java bytecode.

Java, a popular programming language on desktop system, is seldom used in embedded systems. Some features of Java, like thread support in the language, can greatly simplify development of embedded systems, but the common implementations of the JVM (Java Virtual Machine), as interpreter or just-in-time compiler, are not practical.

This site describes an alternative approach: JOP (a Java Optimized Processor) is a hardware implementation of the JVM with predictable execution time for embedded real-time systems.

Due to the small size of the processor, it can be implemented in a low cost FPGA. For low volume systems, the flexibility of an FPGA can be of more importance then the slightly higher cost compared to conventional processors.

JOP is one way to use a configurable Java processor in small embedded real-time systems. It shall help to increase the acceptance of Java for these systems.

Complete VHDL source and tools in Java are available for download from this site. If you prefere CVS access you can get the sources from For discussion with other JOP users a yahoo group is available ( Click to join java-processor ).


March, 2006:  LEON, the GPL version of Sun's SPARC V8 from Gaisler Research, is available for the Cyclone Board ( leon-jopdesign-ep1c12.tar.gz)

July, 2005:  An open-source IO board for DSP applications with the Cyclone board is developed by the SoC group at the Vienna University of Technology.

April, 2005:  A SD Card connector for the baseio.

March, 2005:  The thesis is available.

November, 2004:  A yahoo group is available for discussion and support of JOP and related topics (e.g. embedded and real-time Java). Click to join java-processor

Added a Spartan-3 version for the Trenz retro board. The design flow is the same as with the Xilinx board.

October, 2004:  JOP is ported to the Xilinx Spartan-3 Starter Kit. This kit is a nice and very cheap ($ 99) solution. The on-board memory is 1MB SRAM (the same amount/speed as on the Cyclone board), but the Flash is a little bit small for configuration and application data.

To get started:

  • Compile the ISE project under ../xilinx/s3sk
  • Download JOP to the board
  • Connect a serial cabel from the board to your PC
  • Open a command prompt in ../java/target
  • Change the COM-port in doit.bat
  • type:
    doit test test Clock
Now your first Java program runns on JOP/Spartan-3!

September, 2004:  The Jopcore ACEX board is now released under GPL. Available at:

Martin Schoeberl

Copyright © 2000-2005, DI Martin Schoeberl