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Source code


Name: ao68000
Created: Mar 28, 2010
Updated: Oct 23, 2012
SVN Updated: Feb 24, 2011

Other project properties

Category: Processor
Language: Verilog
Development status: Beta
Additional info:
WishBone Compliant: Yes
License: BSD


The OpenCores ao68000 IP Core is a Motorola MC68000 binary compatible processor.


July 2011: Project copied to (https://github.com/alfikpl/ao68000). Further development of ao68000 will continue on github.


  • CISC processor with microcode,
  • WISHBONE revision B.3 compatible MASTER interface,
  • Not cycle exact with the MC68000, some instructions take more cycles to complete, some less,
  • Uses about 4750 LE on Altera Cyclone II and about 45600 bits of RAM for microcode,
  • Tested against the WinUAE M68000 software emulator. Every 16-bit instruction was tested with random register contents and RAM contents (Processor verification). The result of execution was compared,
  • Contains a simple prefetch which is capable of holding up to 5 16-bit instruction words,
  • Documentation generated by Doxygen (www.doxygen.org) with doxverilog patch ( http://developer.berlios.de/projects/doxverilog/ ). The specification is automatically extracted from the Doxygen HTML output.

WISHBONE compatibility

  • Version: WISHBONE specification Revision B.3,
  • General description: 32-bit WISHBONE Master interface,
  • WISHBONE signals described in IO Ports,
  • Supported cycles: Master Read/Write, Master Block Read/Write, Master Read-Modify-Write for TAS instruction, Register Feedback Bus Cycles as described in chapter 4 of the WISHBONE specification,
  • Use of ERR_I: on memory access – bus error, on interrupt acknowledge: spurious interrupt,
  • Use of RTY_I: on memory access – repeat access, on interrupt acknowledge: generate auto-vector,
  • WISHBONE data port size: 32-bit,
  • Data port granularity: 8-bits,
  • Data port maximum operand size: 32-bits,
  • Data transfer ordering: BIG ENDIAN,
  • Data transfer sequencing: UNDEFINED,
  • Constraints on CLK_I signal: described in Clocks, maximum frequency: about 82 MHz.


  • The ao68000 is used as the processor for the OpenCores aoOCS project - Wishbone Amiga OCS SoC ( http://opencores.org/project,aoocs )
  • It can also be used as a processor in a System-on-Chip booting Linux kernel version up to init program lookup (System-on-Chip example with ao68000 running Linux).

Similar projects

Other free soft-core implementations of M68000 microprocessor include:

  • OpenCores TG68 ( http://www.opencores.org/project,tg68 ) - runs Amiga software, used as part of the Minimig Core,
  • Suska Atari VHDL WF_68K00_IP Core ( http://www.experiment-s.de/en ) - runs Atari software,
  • OpenCores K68 ( http://www.opencores.org/project,k68 ) - no user and supervisor modes distinction, executes most instructions, but not all.
  • OpenCores ae68 ( http://www.opencores.org/project,ae68 ) - no files uploaded as of 27.03.2010.


  • Microcode not optimized: some instructions take more cycles to execute than the original MC68000,
  • TRACE not tested,
  • The core is still large compared to other implementations.


  • Optimize the desgin and microcode,
  • Count the exact cycle count for every instruction,
  • Test TRACE,
  • Write more documentation.


  • April 2010: Tested with WinUAE software MC68000 emulator,
  • April 2010: Booted Linux kernel up to init process lookup,
  • December 2010: Runs as a processor in OpenCores aoOCS project,
  • January 2011: Core area optimization by over 33% (Thanks to Frederic Requin).
  • July 2011: Project copied to (https://github.com/alfikpl/ao68000). Further development of ao68000 will continue on github.


  • Icarus Verilog simulator ( http://www.icarus.com/eda/verilog/ ) is required to compile the tb_ao68000 testbench/wrapper,
  • Access to Altera Quartus II instalation directory (directory eda/sim_lib/) is required to compile the tb_ao68000 testbench/wrapper,
  • GCC ( http://gcc.gnu.org ) is required to compile the WinUAE MC68000 software emulator,
  • Java runtime ( http://java.sun.com ) is required to run the ao68000_tool (ao68000_tool documentation),
  • Java SDK ( http://java.sun.com ) is required to compile the ao68000_tool (ao68000_tool documentation),
  • Altera Quartus II synthesis tool ( http://www.altera.com ) is required to synthesise the soc_for_linux System-on-Chip (System-on-Chip example with ao68000 running Linux).


  • ao68000 - the ao68000 IP Core processor,
  • MC68000 - the original Motorola MC68000 processor.

Structure diagram