One-Hot
One-hot encoding is the default encoding scheme. Its principle is to associate one code bit and also one flip-flop to each state. At a given clock cycle during operation, one and only one bit of the state variable is asserted. Only two bits toggle during a transition between two states. One-hot encoding is very appropriate with most FPGA targets where a large number of flip-flops are available. It is also a good alternative when trying to optimize speed or to reduce power dissipation.
Gray
Gray encoding guarantees that only one bit switches between two consecutive states. It is appropriate for controllers exhibiting long paths without branching. In addition, this coding technique minimizes hazards and glitches. Very good results can be obtained when implementing the state register with T
Compact
Compact encoding consists of minimizing the number of bits in the state variables and flip-flops. This technique is based on hypercube immersion. Compact encoding is appropriate when trying to optimize area.
Johnson
Like Gray, Johnson encoding shows benefits with state machines containing long paths with no branching.
Actual
Sequential
Sequential encoding consists of identifying long paths and applying successive radix two codes to the states on these paths. Next state equations are minimized.
Actual
Speed1
Speed1 encoding is oriented for speed optimization. The number of bits for a state register depends on the particular FSM, but generally it is greater than the number of FSM states. |
