Support of cross calls between a microprocessor and FPGA in CPU-FPGA coupling architecture

The coupling architecture containing an FPGA device and a microprocessor has been widely used to accelerate microprocessor execution. Therefore, there have been intensive researches about synthesizing high-level programming languages (HLL) such as C and C++ into HW in the high-level synthesis community in order to make the work of reconfiguring the FPGA easier. However, the difference in a calling method in terms of semantics between HDLs and HLLs makes their interface implementation very difficult. This paper presents a novel communication framework between a microprocessor and FPGA, which allows the full implementation of cross calls between SW and HW and even recursive calls in HW without any limitation. We show that our proposed calling overhead is very small. With our communication framework, hardware components inside the FPGA are no longer isolated accelerators, and they can work as other master components in a system configuration.