HDLBits Lemmings1-4

Lemming1

网址：https://hdlbits.01xz.net/wiki/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.

两个状态，向左向右，向左时遇见左障碍就转变方向，向右时遇见右障碍转向。

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// State transition logiccase(state)LEFT: next_state=bump_left?RIGHT:LEFT;RIGHT: next_state=bump_right?LEFT:RIGHT;endcaseendalways @(posedge clk, posedge areset) begin// State flip-flops with asynchronous resetif(areset) state<=LEFT;else state<=next_state;end// Output logicassign walk_left = (state == LEFT);assign walk_right = (state == RIGHT);endmodule

Lemming2

网址：https://hdlbits.01xz.net/wiki/Lemmings2

Lemming3

网址：https://hdlbits.01xz.net/wiki/Lemmings3

See also: Lemmings1 and Lemmings2.

In addition to walking and falling, Lemmings can sometimes be told to do useful things, like dig (it starts digging when dig=1). A Lemming can dig if it is currently walking on ground (ground=1 and not falling), and will continue digging until it reaches the other side (ground=0). At that point, since there is no ground, it will fall (aaah!), then continue walking in its original direction once it hits ground again. As with falling, being bumped while digging has no effect, and being told to dig when falling or when there is no ground is ignored.

(In other words, a walking Lemming can fall, dig, or switch directions. If more than one of these conditions are satisfied, fall has higher precedence than dig, which has higher precedence than switching directions.)

Extend your finite state machine to model this behaviour.

在2的基础上多了dig状态，且dig状态也与方向有关，用两个状态分别表示左右，在dig状态时碰撞不影响方向。

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 ); reg [2:0] state,next_state;parameter wl=0,wr=1,dl=2,dr=3,fl=4,fr=5;always @(posedge clk or posedge areset) beginif(areset) state<=wl;else state<=next_state;endalways @(*) begincase(state)wl: beginwalk_left=1;walk_right=0;aaah=0;digging=0;next_state=(ground)?(dig?dl:(bump_left?wr:wl)):fl;endwr: beginwalk_left=0;walk_right=1;aaah=0;digging=0;next_state=(ground)?(dig?dr:(bump_right?wl:wr)):fr;enddl: beginwalk_left=0;walk_right=0;aaah=0;digging=1;next_state=(ground)?dl:fl;enddr: beginwalk_left=0;walk_right=0;aaah=0;digging=1;next_state=(ground)?dr:fr;endfl: beginwalk_left=0;walk_right=0;aaah=1;digging=0;next_state=(ground)?wl:fl;endfr: beginwalk_left=0;walk_right=0;aaah=1;digging=0;next_state=(ground)?wr:fr;endendcaseend
endmodule

Lemming4

网址：https://hdlbits.01xz.net/wiki/Lemmings4

See also: Lemmings1, Lemmings2, and Lemmings3.

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.

在3的基础上增加了掉落时间超过20则口口，需要加入计时器，口口后在复位之前所有输出为零。

本题容易出错的点是计时cnt位宽太少，计时超过位数导致cnt<20,进入错误状态。

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 ); reg [2:0] state,next_state;parameter wl=0,wr=1,dl=2,dr=3,fl=4,fr=5,splat=6;reg [8:0] cnt;always @(posedge clk or posedge areset) beginif(areset) state<=wl;else state<=next_state;endalways @(posedge clk or posedge areset) beginif(areset) cnt<=0;else if(state==fl|state==fr)cnt<=cnt+1;else cnt<=0;endalways @(*) begincase(state)wl: next_state=ground?(dig?dl:(bump_left?wr:wl)):fl;wr: next_state=ground?(dig?dr:(bump_right?wl:wr)):fr;dl: next_state=ground?dl:fl;dr: next_state=ground?dr:fr;fl: next_state=ground?(cnt>=20?splat:wl):fl;fr: next_state=ground?(cnt>=20?splat:wr):fr;splat: next_state=splat;endcaseendalways @(*) begincase(state)wl: begin walk_left=1;walk_right=0;aaah=0;digging=0; endwr: begin walk_left=0;walk_right=1;aaah=0;digging=0; enddl: begin walk_left=0;walk_right=0;aaah=0;digging=1; enddr: begin walk_left=0;walk_right=0;aaah=0;digging=1; endfl: beginwalk_left=0;walk_right=0;aaah=1;digging=0;endfr: beginwalk_left=0;walk_right=0;aaah=1;digging=0;endsplat: begin walk_left=0;walk_right=0;aaah=0;digging=0; endendcaseend
endmodule