In this paper, we propose the target board architecture of a rapid prototyping embedded system based on hardware software codesign. The target board contains a TMS320C30 DSP processor and up to four Xilinx XC4025E FPGAs. Various communication channels between the C30 and the FPGAs are provided and a master-master computing paradigm is supported. HW/SW communication protocols, ranging from handshaking, batch to queue controlled, as well as the corresponding interfaces are described in VHDL and C codes respectively and can be easily augmented to the mapped design. A codesign implementation example based on G.728 LD-CELP speech decoder shows the proposed communication protocols and interfaces lead to very small time and circuitry overhead.