NIFD: Non-intrusive FPGA Debugger -- Debugging FPGA 'Threads' for Rapid HW/SW Systems Prototyping

Debugging hardware has always been difficult when compared to debugging software, in large part due to a lack of convenient visibility. This paper describes the open NIFD framework that provides software-like debugging facilities to both pure FPGA and hybrid FPGA/software platforms, allowing a designer to treat the hardware logic like a specialized remote software debug target. NIFD provides features such as single stepping, breakpoints, and examination of the full hardware state from a standard debug console such as GDB. The framework leverages built-in readback support to enable non-intrusive, transparent debugging with full observability and controllability. This technique is not only useful for debugging, but can also be used in production environments for infrequent events such as the slow sampling of counters.