Verilog专题（二十五）Lemmings4

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题目

Although Lemmings can walk, fall, and dig, Lemmings aren't invulnerable. If a Lemming falls for too long then hits the ground, it can splatter. In particular, if a Lemming falls for more than 20 clock cycles then hits the ground, it will splatter and cease walking, falling, or digging (all 4 outputs become 0), forever (Or until the FSM gets reset). There is no upper limit on how far a Lemming can fall before hitting the ground. Lemmings only splatter when hitting the ground; they do not splatter in mid-air.

Extend your finite state machine to model this behaviour.

Falling for 20 cycles is survivable:

Falling for 21 cycles causes splatter:

 

Module Declaration

module top_module(
    input clk,
    input areset,    // Freshly brainwashed Lemmings walk left.
    input bump_left,
    input bump_right,
    input ground,
    input dig,
    output walk_left,
    output walk_right,
    output aaah,
    output digging );

状态转移图

 

我的设计

module top_module(    input clk,    input areset,    // Freshly brainwashed Lemmings walk left.    input bump_left,    input bump_right,    input ground,    input dig,    output walk_left,    output walk_right,    output aaah,    output digging );​    localparam left = 0;    localparam right = 1;    localparam left_dig = 2;    localparam right_dig = 3;    localparam left_fall = 4;    localparam right_fall = 5;    localparam over = 6;        reg[2:0] state, next_state;    reg[3:0] out;    reg[7:0] cnt;        always@(posedge clk or posedge areset) begin        if(areset)            state <= left;        else            state <= next_state;    end        always@(*) begin        case(state)            left:next_state=ground?(dig?left_dig:(bump_left?right:left)):left_fall;            right:next_state=ground?(dig?right_dig:(bump_right?left:right)):right_fall;            left_dig:next_state=ground?left_dig:left_fall;            right_dig:next_state=ground?right_dig:right_fall;            left_fall:next_state=ground?((cnt>=5'd21)?over:left):left_fall;            right_fall:next_state=ground?((cnt>=5'd21)?over:right):right_fall;            over:next_state=over;        endcase    end        always@(posedge clk or posedge areset) begin        if(areset) begin            out <= 4'b1000;        end        else            case(next_state)                left:begin                    out <= 4'b1000;                    cnt <= 0;                end                right:begin                    out <= 4'b0100;                    cnt <= 0;                end                left_dig:begin                    out <= 4'b0001;                    cnt <= 0;                end                right_dig:begin                    out <= 4'b0001;                    cnt <= 0;                end                left_fall:begin                    out <= 4'b0010;                    cnt = cnt + 1;                end                right_fall:begin                    out <= 4'b0010;                    cnt = cnt + 1;                end                over:out <= 4'b0000;            endcase    end        assign {walk_left, walk_right, aaah, digging} = out;    endmodule

 

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