SimXMD: Simulation-based HW/SW co-debugging

The unique promise of embedded systems in FPGAs is that designers can develop and modify their own peripheral hardware with a high degree of flexibility. However, the task of verifying the hardware commonly involves writing software to interact with it. This software itself is prone to design errors. To debug a system with two untested interacting components, it is preferable if their interaction can be precisely traced. We are presenting SimXMD (Simulation-based eXperimental Microprocessor Debugger), a tool that allows developers to debug microcontroller code and custom hardware simultaneously. The concept of debugging hardware and software together is not a new one. However, we take two established tools already used by the respective developers and connect them in a transparent way. SimXMD connects a GNU debugger (GDB) instance to a full-system simulation of an embedded FPGA system in ModelSim. This enables free-roaming investigation of hardware-software interactions inside the system, including reverting back to an earlier moment in simulation time. Software can be debugged in the same way that it would be commonly done with a real implementation on an FPGA board.