HDLBits- 在线学习Verilog(Problem 127-130)

转载自:知乎
作者:真垃圾

Problem 127 Lemmings1

游戏旅鼠涉及到有非常简单的大脑的生物,我们将会使用有限状态机(FSM)对其建模。

在旅鼠的2D世界中,旅鼠只有两种状态:向左走和向右走。当它遇到一个障碍物的时候,会转变方向。特别是,如果旅鼠被左侧撞到,它将会向右走,被右侧撞到,将会向左走。如果被两侧撞到,它依然会转换方向。

用两状态,两输入,一输出的摩尔型状态机对其行为建模。

module top_module(
    input clk,
    input areset,    // Freshly brainwashed Lemmings walk left.
    input bump_left,
    input bump_right,
    output walk_left,
    output walk_right); //  
    parameter LEFT=0, RIGHT=1;
    reg state, next_state;
    always @(*) begin
        case(state)
            LEFT: next_state = bump_left ? RIGHT:LEFT;
            RIGHT:next_state = bump_right? LEFT:RIGHT;
        endcase// State transition logic
    end
    always @(posedge clk, posedge areset) begin
        if(areset) state <= LEFT;
        else state<=next_state;// State flip-flops with asynchronous reset
    end
    assign walk_left = (state==LEFT);
    assign walk_right= (state==RIGHT);

    // Output logic
    // assign walk_left = (state == ...);
    // assign walk_right = (state == ...);

endmodule

Problem 128 Lemmings2

除了向左和向右,旅鼠在它们脚下地面消失的时候还会掉落(发出“aaah!”)。地面重新出现的时候,旅鼠将会沿着掉落之前的方向继续行走。当旅鼠在地面消失的时候被碰撞(还没有掉落),不会影响步行方向,或者当地面重新出现但旅鼠仍在掉落过程中时,也不会影响步行方向。

用有限状态机(FSM)对此次行为建模。

module top_module(
    input clk,
    input areset,    // Freshly brainwashed Lemmings walk left.
    input bump_left,
    input bump_right,
    input ground,
    output walk_left,
    output walk_right,
    output aaah );
    reg [1:0]state,next;
    parameter WL=0,WR=1,FL=2,FR=3;
    always @(*)
        begin
        case(state)
            WL: next = ground? ( bump_left ? WR:WL):FL;
            WR: next = ground? ( bump_right? WL:WR):FR;
            FL: next = ground? WL : FL;
            FR: next = ground? WR : FR;
        endcase
        end
    always @(posedge clk or posedge areset)
        if(areset) state <= WL;
        else state <= next;
    always @(*)
        case(state)
            WL:  {walk_left,walk_right,aaah}=3'b100;
            WR:  {walk_left,walk_right,aaah}=3'b010;
            FL:  {walk_left,walk_right,aaah}=3'b001;
            FR:  {walk_left,walk_right,aaah}=3'b001;
        endcase
    
            
endmodule

Problem 129 Lemmings3

除了走路和掉落外,旅鼠有时候还能做些有用的事情,比如挖洞(当dig=1时,开始挖洞)

旅鼠在地面的时候(ground=1)它能挖洞,直到到达地面的另一边(ground=0)。在那时,由于没有地面,旅鼠将会下落(发出“aaah”),当它再一次到达地面的时候,继续按照它原来的方向行走。和掉落一样,挖洞过程中被撞击不受影响,而且掉落或者没有地面的时候挖洞命令将会被忽视。

(换句话说,旅鼠能下落、挖洞、或者转变方向。如果多个条件同时满足,优先级是:下落>挖洞>转换方向),扩展你的有限状态机模型来建模其行为。

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 ); 
    parameter WL=0,WR=1,FL=2,FR=3,DL=4,DR=5;
    reg [2:0]state,next;
    //state transtition logic
    always @(*)
        begin
            case(state)
                WL: next = ground? (dig? DL : (bump_left? WR:WL) ):FL;
                WR: next = ground? (dig? DR : (bump_right?WL:WR) ):FR;
                FL: next = ground? WL : FL;
                FR: next = ground? WR : FR;
                DL: next = ground? DL : FL;
                DR: next = ground? DR : FR;
            endcase
        end
    always @(posedge clk or posedge areset)
        if(areset) state <= WL;
        else state <= next;
    always @(*)
        case(state) 
            WL: {walk_left,walk_right,aaah,digging} = 4'b1000;
            WR: {walk_left,walk_right,aaah,digging} = 4'b0100;
            FL: {walk_left,walk_right,aaah,digging} = 4'b0010;
            FR: {walk_left,walk_right,aaah,digging} = 4'b0010;
            DL: {walk_left,walk_right,aaah,digging} = 4'b0001;
            DR: {walk_left,walk_right,aaah,digging} = 4'b0001;    
        endcase
endmodule

Problem 130 Lemmings4

尽管旅鼠能够行走,掉落,挖洞,但也并非无懈可击。如果旅鼠下落过程过长在落到地面,它会飞溅。特别地,如果旅鼠下落超过20个周期再下落到地面,它将会飞溅,停止行走,掉落和挖掘(所有的4个输出都将为0),除非FSM复位。旅鼠能够下落多远没有上限。旅鼠仅仅会在落到地面的时候飞溅,而不会在半空飞溅。

扩展你的有限状态机模型来建模其行为。

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 ); 
    parameter WL=0,WR=1,FL=2,FR=3,DL=4,DR=5,Splat = 6;
    reg [64:0]counter;
    reg [2:0]state,next;
    always @(*)
        case(state)
            WL: next = ground ? (dig ? DL: (bump_left?WR:WL)) : FL;
            WR: next = ground ? (dig ? DR: (bump_right?WL:WR)) : FR;
            FL: next = ground ? (counter>19? Splat : WL) : FL;
            FR: next = ground ? (counter>19? Splat : WR): FR;
            DL: next = ground ? DL : FL;
            DR: next = ground ? DR : FR;
            Splat:next = Splat;
        endcase
    always @(posedge clk or posedge areset)
        begin
        if(areset) state<=WL;
        else if  ( state==FL || state == FR )             
                          begin
                              state <= next;
                              counter = counter + 1;
                          end
 
        else begin 
            state <= next;  
            counter =0;
        end
        end
            
    always @(*)
        case(state)
            WL : {walk_left,walk_right,aaah,digging} = 4'b1000;
            WR : {walk_left,walk_right,aaah,digging} = 4'b0100;
            FL : {walk_left,walk_right,aaah,digging} = 4'b0010;
            FR : {walk_left,walk_right,aaah,digging} = 4'b0010;
            DL : {walk_left,walk_right,aaah,digging} = 4'b0001;
            DR : {walk_left,walk_right,aaah,digging} = 4'b0001;
            Splat: {walk_left,walk_right,aaah,digging} = 4'b0000;  
        endcase 
    
endmodule

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