Choosing architecture

Question

Hi,
For my next project (academic, hobby), I am planning to add fine-grained multi-threading support to an existing open-source processor architecture. The OpenSPARC already includes this and I'll use it as a reference when needed. What I am thinking is to take another existing core from opencores.org and add this functionality. I have several questions to ask the experienced community.
My main decision now floats aroud selecting the core which will not only allow me to do this project, but also reuse my work in future multi-core, multi-threaded projects. That means that the open source I need to choose should be:
- an active project, so I am not the only person working on hardware/software support
- popular architecture/instruction set (mips, risc, v8, v9) to become fluent with industrially used uProcessors
- synthesizable steady code
- VHDL because that's what I know and I am short on time
With these in mind, I identified a few cores and would like to hear your opinion:
- what is the potential complexity
- how can tool availability affect this decision (leon3, openspac have lots)
- if Leon3, what's the potential to contribute to the community (it is mostly maintained by Gaisler research and not an individual after all)
Leon3
Tested, verified
Asic and FPGA-proven
VHDL
Open source, however is maintained by Gaisler Research in Sweden
Has a lot of tools, support and commercial interest (used for space missions)
Can be easily used for future projects due to above, so it is worth learning it
Plasma
FPGA-proven
VHDL
Active project started in 2001, maintained by an individual
Has success stories (complete TCP/IP stack implemented; robot control)
Potentially good processor for future projects
I am more inclined to use this core since it is not owned by any company, yet still supports tools and can be used in future
I can contribute to opensource community here
Open8 uRISC
Stable and active
VDHL
Supports v8 instructions
Comments:
I am not familiar with v8 and not sure whether it will be a better experience compared to other uPs.
OpenSPARC
Verilog--not familiar with
can use manuals and code as a reference

Answer 1

Hi.
From the processors that you mentioed I believe that the most complex and the most advanced is the Leon 3 processor. There is also a thesis that compares the Leon 3, the OpenRISC core and the microblaze, I think, processor cores in performance. Also Leon 3 has multicore support. During the last years I worked with Plasma core and the OpenRISC core (now with the OpenSPARC which is much more complicated) and I know both of them very well. For adding fine-grained multi-threading support, I believe that the best choises are the Leon 3 and the OpenRISC core. I can give you some usefull information about OpenRISC. OpenRISC has L1 instruction and data cache memories and a wishone interface that connects the processor core with the external memory. Wishbone interface can be configured as shared bus or a crossbar switch interconnection scheme. By default in OpenRISC is shared bus. The wishbone can gine you the opportunity to add more than one multithreaded cores at your final design. There is also a thesis in the net that creates a multicore OpenRISC (not multitreaded). Unfortunatelly I don't have the same knowlenge about Leon 3 processor and I can't help you so much but you can ask at Gaisler Research team.
Finally verilog I think that is easier than vhdl. At the beginning of my thesis I also have the same problem with you, but when I started using the verilog for the OpenSPARC core I forgot the vhdl. It is also an opportunity for you to learn more than one language.
Andreas