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I am doing a study on FPGA interfacing with microprocessors such as ARM9.
I found the concept of soft core processors and hard core processors in my study. May I know what is the comparison between these two types, the similarities and differences in the implementation?
Soft core is implemented in FPGA fabric while Hard is implemented the same as any integrated circuit while still connected to the FPGA fabric. The comparison generally boils down to:
Hard Core Processors - 100's of MHz up to 1GHz+ of speed
Soft Core Processors - 250MHz and less (usually less than 200MHz)
In recent years, there's been a large move towards hard processor primarily due to the need for faster processing that the soft cores can't provide. When you put a hard core processor with the FPGA fabric, you can typically enable processing of a lot of data, which is needed for communication infrastructure applications (lots of GBs of data going by), for example.
A soft-core processor is a processor implemented using the FPGA fabric.
A hard-core processor is a processor that's actually physically implemented as a structure in the silicon.
Basically, you can add a soft-core processor to a FPGA-based system after it's already designed. However, adding a hard-core processor requires either a different FPGA, or an additional chip on the board.
Hard-core processors are preferred when possible because the price/computing-power ratio for a hardware CPU is much better. Implementing a CPU in FPGA fabric is very resource intensive, particularly if you want a lot of computing power. The equivalent hardware CPU is likely much cheaper.
Not only is the hardware CPU much cheaper, but it is also likely to be much more energy efficient. In battery-operated platforms, efficiency is crucial for long battery life. Unused gates in an FPGA can sometimes be turned off, but usually there are far more active circuits in a soft core processor than in a purpose-design hardware CPU. All of that potential FPGA silicon consumes power.
Implementing soft processor to achieve a certain functionality might be cheaper in terms of purchasing the hardware in comparison to purchasing equivalent hard processor.
