SoftCore Processors

A softcore processor in its simplest sense can be defined as a HDL(Verilog/Vhdl) code with which an FPGA can be programmed so that it behaves like a processor.That is ,it enables us to built a processor system which we can configure ourselves inorder to optimize the perfomance to meet our requirements.
The most successful of the commercial processors like ARM have distinguished themselves in being suited to a large no.of different purposes as well as being cost effective.The ability to achieve real time operation also remains as its trademark.The softcore processsor on the other hand is unique for its reconfigurability.It can we configured as a fast system for achieving real time operations as well as a small system in case of size constrained projects.Various embedded peripherals like timers, uart blocks,dma blocks SDRAM memories are also available along with the processor in softcore form so that we can choose among the available components ,those we require to built our own custominzed processor system.The design can be modified at will any time.
The design of a softcore processor system can be done in very short time using the CAD software provide by the various FPGA vendors. We just have to pick the required configuration of the processor as well as choose the associated components.The software will generate the code for the components.But the best part is that the interfacing logic between various components also is generated by the tool.This saves much of our time as don't have to worry about interfacing between different components which may be different in bit length,speed,memory etc.Once the system design is finished we can straight away burn the code to our FPGA using the same tool and then test the system.we can run the our code working code on the system by making a little variations that make it compatible with the components used.The processor system provides a function rich API for accessing the components in our system and we can use them easily to modify our code.So no extra effort is needed to learn any new language or so...
The most popular softcore processors available in the market are microblaze from Xilinx and Nios II from Altera.For more information checkout these links

http://www.xilinx.com/xlnx/xebiz/designResources/ip_product_details.jsp?key=micro_blaze

http://www.altera.com/products/software/products/nios2/emb-nios2_ide.html