Additional PFR solutions are available for implementing NIST SP800-193, such as the Lattice Root of Trust FPGA solution (see Figure 4-12).
The difference in implementations is hardware RoT device selection. Selections include processor microcode, CPLD devices, or FPGA devices. Each has its particular advantages and disadvantages. For example, processor microcode has a limited protection scope, which is why many customers use add-on devices for hardware RoT (CPLD, FPGA).