Finite State Machine: Realization

1. Finite State Machine:Realization Martinet Lee, SteveChung

2. Outline • What is FSM? • The theory • Not only a theory • Now, forget about FSM • Implementing functions, by circuit • Implementing functions, by logic • When circuit meets logic, FSM • A simple example: from functions to FSM to circuit

3. What is FSM?

4. The Theory

5. Not only a theory… • You know how it looks like  • But how to construct it?How to connect it with the target function?

6. Now, Forget about FSM

7. Implementing functions, by circuit • Function: Simple Traffic Light: Red Green  Yellow  Red(repeat) • Construct a counter which will reset on 2 : • 0  1  2  0 … • 2’b00  2’b01  2’b10  2’b00  … • Construct the lights according to the counter’s value.

8. Implementing functions, by circuit • Function: Find target , identify target ( enemy and ally ) , act accordingly ( fire, supply ), then repeat. • How to construct? • Counter?

9. Implementing functions, by Logic • Function: Find target , identify target ( enemy and ally ) , act accordingly ( fire, supply ), then repeat. • How to construct? • Search  Found  if( target == Enemy ) Fire; else Supply; Search

10. When Circuit meets Logic:Finite State Machine

11. Finite State Machine • Function: Find target , identify target ( enemy and ally ) , act accordingly ( fire, supply ), then repeat. • Aintuitive mapping from “function” to “FSM graph” • But how to implement?

12. Finite State Machine Implementation • Create a set of registers, to store STATE • Assign each state on FSM to a number • Search  0  3’b000 • Found  1  3’b001 • Enemy  2  3’b010 • Ally  3  3’b011 • Fire  4  3’b100 • Supply  5  3’b101 • A circuit that could differentiate enemy and ally, will produce a 1-bit signal.

13. FINITE STATE MACHINE IMPLEMENTATION • reg [2:0] State;reg [2:0] nextState;regdetected_smth;regisenemy;always@(posedgeclk)beginif(reset == 1’b1) State <= 3’b000; else begin State <= nextState; endendalways@(*) begincase(State) 3’b000: if(detected_smth == 1’b1) nextState = 3’b001; elsenextState = 3’b000; 3’b001: if( isenemy == 1’b1)nextstate = 3’b010; elsenextstate = 3’b011; 3’b010: nextState = 3’b100; 3’b011: nextState= 3’b101; 3’b100: nextState = 3’b000; 3’b101: nextState = 3’b000; default: nextState = 3’b000;endcaseend

14. Code Not Clear enough… • Use parameter! • parameter S_Search = 3’b000;parameter S_Found = 3’b001;parameter S_Enemy = 3’b010;parameter S_Ally = 3’b011;parameter S_Fire = 3’b100;parameter S_Supply = 3’b101;

15. Overall Code • reg [2:0] State;reg [2:0] nextState;regdetected_smth;regisenemy;parameter S_Search = 3’b000;parameter S_Found = 3’b001;parameter S_Enemy = 3’b010;parameter S_Ally = 3’b011;parameter S_Fire = 3’b100;parameter S_Supply = 3’b101;always@(posedgeclk)begin if(reset == 1’b1) State <= S_Search; else begin State <= nextState; endendalways@(*) begin case(State)S_Search: if(detected_smth == 1’b1) nextState = S_Found; elsenextState = S_Search;S_Found: if( isenemy == 1’b1)nextstate = S_Enemy; elsenextstate = S_Ally;S_Enemy:nextState = S_Fire;S_Ally:nextState = S_Supply;S_Fire:nextState = S_Search;S_Supply:nextState = S_Search; default: nextState = S_Search;endcaseend

16. Any Questions? 