FPGA: use PWM wave to control LED brightness

Preface

Text

Knowledge points used ：

1. Use the method of detecting the falling edge to eliminate the shaking of keys
2. By generating triangular waves , And then realize variable duty cycle PWM wave
3. Generate incremental 、 Decreasing signal

Design documents

// 4 Adjust the brightness once 
//  Press next 4 Next time , The brightness decreases in turn 
module pwm_led_02(
	input 				    clk,
	input 				    rst_n,
	input 				    key,
	
	output reg 				led
);

parameter CNT_MAX = 12'd1249;
parameter PWM_2   = 12'd249;
parameter PWM_4   = 12'd499;
parameter PWM_6   = 12'd749;
parameter PWM_8   = 12'd999;

reg [11:0]PWM_type;
wire key_nege;// The falling edge of the key 

reg key_reg1;
reg key_reg2;

reg cnt_up;
reg cnt_down;

reg key_up;
reg key_down;

reg [2:0]  cnt_key;
reg [11:0] cnt_1249;
//====================================
// Detect the falling edge of the key 
[email protected](posedge clk or negedge rst_n)begin
	if(!rst_n )begin
		key_reg1 <= 1'd0;
		key_reg2 <= 1'd0;
	end
	else begin
		key_reg1 <= key;
		key_reg2 <= key_reg1;		
	end	
end

assign key_nege = key_reg2 & (~key_reg1);
//====================================


//====================================
//  use 50MHZ Clock generation 20KHZ Of PWM
// Generating triangular waves 

[email protected](posedge clk or negedge rst_n)begin
	if(!rst_n )
		cnt_1249 <= 12'd0;
	else if(key_nege)
		cnt_1249 <= 12'd0;
	else if(cnt_up)
		cnt_1249 <= cnt_1249 + 1;
	else if(cnt_down)
		cnt_1249 <= cnt_1249 - 1;
	else
		cnt_1249 <= cnt_1249;
end

[email protected](posedge clk or negedge rst_n)begin
	if(!rst_n )begin
		cnt_up   <= 1'd0;
		cnt_down <= 1'd0;
	end
	else if(cnt_1249 == CNT_MAX-1)begin
		cnt_up   <= 1'd0;
		cnt_down <= 1'd1;
	end
	else if(cnt_1249 == 0)begin
		cnt_up   <= 1'd1;
		cnt_down <= 1'd0;	
	end
	else begin
		cnt_up   <= cnt_up;
		cnt_down <= cnt_down;
	end
end
//====================================
//  Key count 

[email protected](posedge clk or negedge rst_n)begin
	if(!rst_n )
		cnt_key <= 3'd0;
    else if(key_nege)begin
        if(key_up)
            cnt_key <= cnt_key + 1;
        else if(key_down)//cnt_key[0] && 
            cnt_key <= cnt_key - 1;
    end
end

[email protected](posedge clk or negedge rst_n)begin
	if(!rst_n )begin
		key_up   <= 1'd0;
		key_down <= 1'd0;
	end
	else if(cnt_key == 4)begin
		key_up   <= 1'd0;
		key_down <= 1'd1;
	end
	else if(cnt_key == 0)begin
		key_up   <= 1'd1;
		key_down <= 1'd0;	
	end
	else begin
		key_up   <= key_up;
		key_down <= key_down;
	end
end

[email protected](*)begin
	case(cnt_key)
		3'd1:begin
            if(key_up)begin
                PWM_type = PWM_2;
                if(cnt_1249 <= PWM_type)
                    led = 1'd0;
                else if(cnt_1249 > PWM_type )
                    led = 1'd1;
            end
            else if(key_down)begin
                PWM_type = PWM_2;
                if(cnt_1249 <= PWM_type)
                    led = 1'd0;
                else if(cnt_1249 > PWM_type )
                    led = 1'd1;
            end
        end
		3'd2:begin
            if(key_up)begin
                PWM_type = PWM_4;
                if(cnt_1249 <= PWM_type)
                    led = 1'd0;
                else if(cnt_1249 > PWM_type )
                    led = 1'd1;
            end
            else if(key_down)begin
                PWM_type = PWM_4;
                if(cnt_1249 <= PWM_type)
                    led = 1'd0;
                else if(cnt_1249 > PWM_type )
                    led = 1'd1;
            end
			end			
		3'd3:begin
            if(key_up)begin
                PWM_type = PWM_6;
                if(cnt_1249 <= PWM_type)
                    led = 1'd0;
                else if(cnt_1249 > PWM_type )
                    led = 1'd1;
            end
            else if(key_down)begin
                PWM_type = PWM_6;
                if(cnt_1249 <= PWM_type)
                    led = 1'd0;
                else if(cnt_1249 > PWM_type )
                    led = 1'd1;
            end
			end		
		3'd4:begin
            if(key_up)begin
                PWM_type = PWM_8;
                if(cnt_1249 <= PWM_type)
                    led = 1'd0;
                else if(cnt_1249 > PWM_type )
                    led = 1'd1;
            end
            else if(key_down)begin
                PWM_type = PWM_8;
                if(cnt_1249 <= PWM_type)
                    led = 1'd0;
                else if(cnt_1249 > PWM_type )
                    led = 1'd1;
            end
			end		
	default: begin
			PWM_type = CNT_MAX;
			led = 1'd1;
		end
	endcase

end
endmodule 

The test file

`timescale 1ns/1ns

module tb_pwm (
    
);
reg clk,rst_n,key;
wire led;

initial begin
    clk = 1'd0;
    rst_n = 1'd0;
    key = 1'd1;

    # 100
    rst_n = 1'd1;

    # 30000 
    key = 1'd0;
    #20000
    key = 1'd1;
    # 20000
    key = 1'd0;
    #5000
    key = 1'd1;
    # 10000
    key = 1'd0;
    # 30000
    key = 1'd1;
    # 20000
    key = 1'd0;
    #5000
    key = 1'd1;
    # 10000
    key = 1'd0;
    # 30000
    key = 1'd1;
    # 30000 
    key = 1'd0;
    #20000
    key = 1'd1;
    # 20000
    key = 1'd0;
    #5000
    key = 1'd1;
    # 10000
    key = 1'd0;
    # 30000
    key = 1'd1;
    # 20000
    key = 1'd0;
    #5000
    key = 1'd1;
    # 10000
    key = 1'd0;
    # 30000
    key = 1'd1;
end
always #10 clk = ~ clk;
pwm_led_02 pwm_led_inst(
	.clk(clk),
	.rst_n(rst_n),
	.key(key),
	
	.led(led)
);


endmodule

On board test