# FASM Proof of Concept using Vivado Partial Reconfig flow
harness.v is a top-level design that routes a variety of signal into a black-box region of interest (ROI). Vivado’s Partial Reconfiguration flow (see UG909 and UG947) is used to implement that design and obtain a bitstream that configures portions of the chip that are currently undocumented.
Designs that fit within the ROI are written in FASM and merged with the above harness into a bitstream with fasm2frame and xc7patch. Since writting FASM is rather tedious, rules are provided to convert Verilog ROI designs into FASM via Vivado.
make rules are provided for generating each step of the process so that intermediate forms can be analyzed. Assuming you have a .fasm file, invoking the %_hand_crafted.bit rule will generate a merged bitstream:
make foo.hand\_crafted.bit # reads foo.fasm
## Using Vivado to generate .fasm
Vivado’s Partial Reconfiguration flow can be used to synthesize and implement a ROI design that is then converted to .fasm. Write a Verilog module that _exactly_ matches the roi blackbox model in the top-level design. Note that even the name of the module must match exactly. Assuming you have created that design in my_roi_design.v, ‘make my_roi_design_hand_crafted.bit’ will synthesize and implement the design with Vivado, translate the resulting partial bitstream into FASM, and then generate a full bitstream by patching the harness bitstream with the FASM. non_inv.v is provided as an example ROI design for this flow.