HDLBits-Lemmings1

The game Lemmings involves critters with fairly simple brains. So simple that we are going to model it using a finite state machine.

In the Lemmings' 2D world, Lemmings can be in one of two states: walking left or walking right. It will switch directions if it hits an obstacle. In particular, if a Lemming is bumped on the left, it will walk right. If it's bumped on the right, it will walk left. If it's bumped on both sides at the same time, it will still switch directions.

Implement a Moore state machine with two states, two inputs, and one output that models this behaviour.

Lemmings1 - HDLBits (01xz.net)

See also: Lemmings2, Lemmings3, and Lemmings4.

module top_module(
    input clk,
    input areset,    // Freshly brainwashed Lemmings walk left.
    input bump_left,
    input bump_right,
    output walk_left,
    output walk_right);   
    reg state, next_state;
    parameter left = 0,
              right = 1;
    always @(*) begin
        case(state) 
            left: if(bump_left)begin 
                next_state <= right;
            end
                else
                    next_state <= left;
            right:if(bump_right)begin 
                next_state <= left;
            end
                else
                next_state <= right;
        endcase
    end

    always @(posedge clk, posedge areset) begin
        if(areset)begin 
            state <= left;
        end
        else
            state <= next_state;
    end

    // Output logic
     assign walk_left = (state == left);
     assign walk_right = (state == right);

endmodule