FSM_ENCODING controls encoding on the
state machine. Typically, the Vivado tools choose an encoding
protocol for state machines based on heuristics that do the best for the most designs.
Certain design types work better with a specific encoding protocol.
FSM_ENCODING can be placed on the
statemachine registers. The legal values for this are one_hot, sequential, johnson, gray, user_encoding, and none.
The auto value is the default, and allows the tool to
determine best encoding. The user_encoding value tells
the tool to still infer a statemachine, but to use the encoding given in the RTL by the
user.
The FSM_ENCODING attribute can be set in the RTL or the
XDC.