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Examine soft-core processors for embedded systems

Posted: 21 Jan 2013 ?? ?Print Version ?Bookmark and Share

Keywords:microprocessor? embedded system? FPGA? microcontroller?

Pros
???Everything is open source. RTL source code is available.
???The ORPSoC reference platform makes it easy to implement an OpenRISC system
???The GNU toolchain is fully supported
???A large user community can help solve problems

Cons
???Few FPGA development boards are supported
???Complicated debug solutions
???The Wishbone bus is somewhat outdated
???The OpenCores website is confusing
???Many IP blocks are not maintained

Summary
Using the OpenRISC 1200 soft-core processor is a mixed bag. It is hard to find the way through the OpenCores website and there is no obvious starting point for a newbie. But after finding and downloading the hardware and software support files, it is rather easy to build a system and install Linux if choosing the right FPGA development board.

The Nios II
The Nios II is a proprietary 32bit RISC architecture processor core developed by Altera for use in their FPGAs. The soft-core nature of the Nios II processor lets the system designer specify and generate a custom Nios II core, tailored for his or her specific application requirements. System designers can extend the Nios II's basic functionality by adding a predefined memory management unit and/or defining custom instructions and custom peripherals.

Pros
???Easy-to-use development environment
???No licence required for building a system when using the Quartus II Web Edition
???No extra JTAG programming tool needed

Cons
???Can only be used in Altera FPGAs
???Some IP cores have time-limited licences that will stop working after some time. They will continue to work as long as the development board is connected to your host computer.

Summary
The Altera Quartus II and Nios II Embedded Design Suite make it very easy to build a NIOS II-based system and to write application software that will run on this system. The complete Nios II system is specified in the Qsys tool where the processor is configured and all other system components are added.

Performance measurements
The CoreMark benchmark C-programs were downloaded and installed for the different processors. The program suite was compiled using the GCC compiler that was part of the SDK installation. The results are as follows:

To be totally honest, you should take these values "with a grain of salt," because the processors cores were implemented on different development boards and different GCC compiler versions were used.

Conclusion
I hope that this investigation will help you in deciding with soft-core processor to use. If you want to find out more, I would recommend that to build your own system using a similar setup as described in this article. Hands-on experience is worth much more than reading colourful sales brochures.

About the author
Sven-Ake Andersson is Senior ASIC/FPGA designer at Realtime Embedded.

To download the PDF version of this article, click here.


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