測量占空比

最近嘗試了很多方法測量占空比，雖然說原理簡單，但是測量的時候誤差還是挺大的，凡是沒呢么容易，

最后終於實現了1HZ-5M 占空比的測量，精度小於%0.1

另外發現了一個問題，fpga一條語句如果很復雜的話，可能會出現問題。

例如 assign  duty_altera = pinlv << 1 + pinlv;也就是pinlv_altera 是頻率的三倍，在sigtab仿真時出錯了，如果把這兩條語句分開寫就沒毛病了。

這說明在200M高速頻率下，這樣寫法不太好，跑不了高速。

程序思路：

設定一個1S鍾的閘門，在閘門有效期間測量高電平持續時間和低電平持續時間，需要注意的是：

在測量時間時需要以邊沿做為開始計數的標志，否則程序容易崩潰。然而實際測量出來，還是有誤差的，經過測量多組數據發現：高電平測量的時間所記錄的個數比實際上少記錄了2*pinlv個，而低電平恰恰相反。經過補償，滿足題目的要求。

module    duty(
        //system    interface
        input                clk,
        input                rst_n,
        //sig        interface
        input                sig_in,
        //pinlv        interface
        input        [31:0]    pinlv,
        //user        interface
        output    reg    [15:0]    duty,
        output    reg    [31:0]    cnt_high,
        output    reg    [31:0]    cnt_low,
        output                high_pulse,
        output                low_pulse,
        output        [31:0]    duty_alter
);

//buffer
reg        sig_in_buffer;
reg        sig_in_buffer1;
always @(posedge clk or negedge rst_n)
begin
    if(!rst_n)
    begin
        sig_in_buffer  <= 0;
        sig_in_buffer1 <= 0;
    end
    else
    begin
        sig_in_buffer  <= sig_in;
        sig_in_buffer1 <= sig_in_buffer;
    end
end
assign        high_pulse =  (sig_in_buffer == 1 && sig_in_buffer1 == 0) ? 1 : 0;
assign        low_pulse  =  (sig_in_buffer == 0 && sig_in_buffer1 == 1) ? 1 : 0;
//parameter        CNT_1S = 32'd199_9;
parameter        CNT_1S = 32'd199_999_999;
reg        [31:0]    cnt_1s;
reg                fgate;

always @(posedge clk or negedge rst_n)
begin
    if(!rst_n)
        cnt_1s <= 0;
    else if(cnt_1s >= CNT_1S)
        cnt_1s <= 0;
    else 
        cnt_1s <= cnt_1s + 1;
end

always @(posedge clk or negedge rst_n)
begin
    if(!rst_n)
        fgate <= 0;
    else if(cnt_1s == CNT_1S)
        fgate <= ~fgate;
    else
        fgate <= fgate;
end


reg        fstart;
always @(posedge sig_in_buffer1 or negedge rst_n)
begin
    if(!rst_n)
        fstart <= 0;
    else if(fgate)
        fstart <= 1;
    else
        fstart <= 0;
end
reg        [2:0]        state_high;
reg        [2:0]        state_low;
//cnt
reg        [31:0]        cnt_high_temp;
reg        [31:0]        cnt_low_temp;

always @(posedge clk or negedge rst_n)
begin
    if(!rst_n)
        state_high <= 0;
    else
    case(state_high)
    2'd0 :
    begin
        if(high_pulse)
            state_high <= 2'd1;
        else
            state_high <= 2'd0;
    end
    
    2'd1 :
    begin
        if(low_pulse)
            state_high <= 2'd0;
        else
            state_high <= 2'd1;
    end
    
    default : ;
    endcase
end

always @(posedge clk or negedge rst_n)
begin
    if(!rst_n)
        state_low <= 0;
    else
    case(state_low)
    2'd0 :
    begin
        if(low_pulse)
            state_low <= 2'd1;
        else
            state_low <= 2'd0;
    end
    
    2'd1 :
    begin
        if(high_pulse)
            state_low <= 2'd0;
        else
            state_low <= 2'd1;
    end

    default : ;
    endcase
end
always @(posedge clk or negedge rst_n)
begin
    if(!rst_n)
        cnt_high_temp <= 0;
    else if(fstart)
    begin
        if(state_high == 1)
            cnt_high_temp <= cnt_high_temp + 1;
        else
            cnt_high_temp <= cnt_high_temp;
    end
    else
        cnt_high_temp <= 0;    
end

always @(posedge clk or negedge rst_n)
begin
    if(!rst_n)
        cnt_low_temp <= 0;
    else if(fstart)
    begin
        if(state_low == 1)
            cnt_low_temp <= cnt_low_temp + 1;
        else
            cnt_low_temp <= cnt_low_temp;
    end
    else
        cnt_low_temp <= 0;    
end
wire    [31:0]    pinlv1;
assign    pinlv1     = pinlv << 1;
assign    duty_alter =  pinlv << 1;

always @(negedge fstart or negedge rst_n)
begin
    if(!rst_n)
    begin
        cnt_high <= 0;
        cnt_low <= 0;
    end
    else
    begin
        cnt_high <= cnt_high_temp + duty_alter ;
        cnt_low  <= cnt_low_temp  - duty_alter ; 
    end
end






endmodule