While FPGA interconnect networks were originally designed to connect logic block output pins to input pins, FPGA users and architects sometimes become motivated to create connections between pins and specific wires in the interconnect. These pin-to-wire connections are motivated by both a desire to employ routing-by-abutment, in modular, pre-laid out systems, and to make direct use of resources in the fabric itself. The goal of this work is to measure the difficulty of forming such pin-to-wire connections. We show that compared to a flat placement of the complete system, the routed wirelength and critical path delay increase by 6% and 15% respectively, and the router effort increases 3.5 times. We show that while pin-to-wire connections impose increased stress on the router, they can be used under some circumstances. We also measure the impact of increasing routing architecture flexibility on these results, and propose a low-cost enhancement to improve pin-to-wire routing.

While FPGA interconnect networks were originally designed to connect logic block output pins to input pins, FPGA users and architects sometimes become motivated to create connections between pins and specific wires in the interconnect. These pin-to-wire connections are motivated by both a desire to employ routing-by-abutment, in modular, pre-laid out systems, and to make direct use of resources in the fabric itself. The goal of this work is to measure the difficulty of forming such pin-to-wire connections. We show that compared to a flat placement of the complete system, the routed wirelength and critical path delay increase by 6% and 15% respectively, and the router effort increases 3.5 times. We show that while pin-to-wire connections impose increased stress on the router, they can be used under some circumstances. We also measure the impact of increasing routing architecture flexibility on these results, and propose a low-cost enhancement to improve pin-to-wire routing.