A run-time RTL debugging methodology for FPGA-based co-simulation

Logic simulation provides SoC verification with full controllability and observability, but it suffers from very slow simulation speed for complex design. Using hardware emulation such as FPGA can have higher simulation speed. However, it is very hard to debug due to its poor visibility. FPGA-based cosimulation seems to draw a balance, but Design Under Test (DUT) still resides in FPGA and remains hard for debugging. So a run-time RTL debugging methodology for FPGA-assisted verification system is presented. This method provides internal nodes probing on an event-driven cosimulation platform and achieves full observability for DUT. The debugging tools are embedded in HDL simulator using Verilog VPI callback, so signals of testbench and internal nodes of DUT can be observed in a single waveform and updated as simulation runs, making debugging more efficient. The proposed debugging method connects internal nodes directly to a PCI-extended bus, instead of inserting extra scan-chain logic, so the overhead for area is reduced. Our experiment shows that, compared with a similar method in, the area overhead for debug logic is reduced by 30~50% and compile time is shortened by 40~70%.