either, as it requires the CPU to be reverse engineered. WDC does offer
what is called an RTL (Register Transfer Level) description of the 65816.
This means they have described the internal interactions of the 65816, thus
allowing someone who knows what they're doing to model the CPU in a
hardware description language. Its still not simple though, it would still
require a significant amount of work, and then the TWGS itself would have
to be redesigned to use an FPGA (field programmable gate array, a
reconfigurable logic device) instead of a physical CPU.