Most everyone would agree how important FPGA prototyping is to test and validate an IP, sub-system, or a complete SoC design. Before the design is taped-out it can be validated at speeds near real operating conditions with physical peripherals and devices connected to it instead of simulation models. At the same time, these designs are not purely hardware, but these days incorporate a significant amount of the software stack and so co-verification of hardware and software is put at high importance among other requirements in the verification plan.
However, preparing a robust FPGA prototype is not a trivial task. It requires strong hardware skills and spending a lot of time in the lab to configure and interconnect all required peripheral devices with an FPGA base board. Even more difficult is to create a comprehensive test scenario which contains procedures to configure various peripherals. Programming hundreds of registers in proper sequence and then reacting on events, interrupts, and checking status registers is a complex process. The task which is straightforward during simulation, where full control over design is assured, becomes extremely hard to implement in an FPGA prototype. Facing this challenge, verification engineers often connect a microprocessor or microcontroller daughter card to the main FPGA board. The IP or SoC subsystem you are designing will be connected with some kind of CPU anyhow, so this way seems natural. Having a CPU connected to the design implemented in an FPGA facilitates creating programmatically reconfigurable test scenarios and enables test automation. Moreover, the work of software developers can be now reused as the software stack with device drivers can become a part of the initialization procedure in the hardware test.. The software can become a part of the initialization procedure in the hardware test. If that makes sense to you, then why not use an FPGA board that has all you need – both FPGA and the CPU?