The OpenCores ao68000 IP Core is a Motorola MC68000 compatible processor.
Features
- 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 4810 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 90 MHz.
Use
Similar projects
Other free soft-core implementations of M68000 microprocessor include:
Limitations
- 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.
TODO
- Optimize the desgin and microcode,
- Count the exact cycle count for every instruction,
- Test TRACE,
- Write more documentation.
Status
- 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).
Requirements
Glossary
- ao68000 - the ao68000 IP Core processor,
- MC68000 - the original Motorola MC68000 processor.