Question

这是我的Verilog代码的一部分：

reg [5:0] channel[0:7];
reg [5:0] tmp[0:7];
reg [2:0] counter_out;
reg [2:0] scounter_samp;
reg [2:0] scounter_bits;
...
always @(posedge clk, posedge rst) begin
if(rst) begin
    done          <= 1'b0;
    counter_out   <= 7;
    scounter_samp <= 0;
    scounter_bits <= 0;
    tmp[0] <= 6'b0;
    tmp[1] <= 6'b0;
    ...
    channel[0] <= 6'b0;
    ...
end
else begin
    ...
    if(done==1'b1) begin
        data_out    <= channel[counter_out];
        counter_out <= counter_out-1;
        if(counter_out==0) begin
            done        <= 1'b0;
            counter_out <= 7;
        end
    end
    tmp[scounter_samp][scounter_bits] <= !input_data[8];
    scounter_samp <= scounter_samp + 1;
    if(scounter_samp==7) begin
        scounter_samp <= 0;
        scounter_bits <= scounter_bits + 1;
        if(scounter_bits==5) begin
            done          <= 1'b1;
            scounter_bits <= 0;
            channel[0] <= {tmp[0][5:1],!input_data[8]};
            channel[1] <= tmp[1];
            channel[2] <= tmp[2];
            channel[3] <= tmp[3];
            channel[4] <= tmp[4];
            channel[5] <= tmp[5];
            channel[6] <= tmp[6];
            channel[7] <= tmp[7];
        end
    end
    ...
end

这是我的问题所在：当我在行为模拟中运行Xilinx ISE 13.1时，它可以很好地工作，但在翻译后模拟中，ISE会生成警告：

WARNING:Xst:1710 - FF/Latch <channel_0_1> (without init value) has a constant value of 0 in block <adc_ctr>. This FF/Latch will be trimmed during the optimization process.
WARNING:Xst:1895 - Due to other FF/Latch trimming, FF/Latch <channel_0_2> (without init value) has a constant value of 0 in block <adc_ctr>. This FF/Latch will be trimmed during the optimization process.
WARNING:Xst:1895 - Due to other FF/Latch trimming, FF/Latch <channel_0_3> (without init value) has a constant value of 0 in block <adc_ctr>. This FF/Latch will be trimmed during the optimization process.
WARNING:Xst:1895 - Due to other FF/Latch trimming, FF/Latch <channel_0_4> (without init value) has a constant value of 0 in block <adc_ctr>. This FF/Latch will be trimmed during the optimization process.
WARNING:Xst:1895 - Due to other FF/Latch trimming, FF/Latch <channel_0_5> (without init value) has a constant value of 0 in block <adc_ctr>. This FF/Latch will be trimmed during the optimization process.
WARNING:Xst:1895 - Due to other FF/Latch trimming, FF/Latch <channel_1_0> (without init value) has a constant value of 0 in block <adc_ctr>. This FF/Latch will be trimmed during the optimization process.
WARNING:Xst:1895 - Due to other FF/Latch trimming, FF/Latch <channel_1_1> (without init value) has a constant value of 0 in block <adc_ctr>. This FF/Latch will be trimmed during the optimization process.
WARNING:Xst:1895 - Due to other FF/Latch trimming, FF/Latch <channel_1_2> (without init value) has a constant value of 0 in block <adc_ctr>. This FF/Latch will be trimmed during the optimization process.
WARNING:Xst:1895 - Due to other FF/Latch trimming, FF/Latch <channel_1_3> (without init value) has a constant value of 0 in block <adc_ctr>. This FF/Latch will be trimmed during the optimization process.
...
WARNING:Xst:2404 -  FFs/Latches <channel_0<5:1>> (without init value) have a constant value of 0 in block <adc_ctr>.
WARNING:Xst:2404 -  FFs/Latches <channel_1<5:0>> (without init value) have a constant value of 0 in block <adc_ctr>.

由于这些修整，所有通道的输出数据均为零，但通道[0] [0]。输入数据不断变化，因此通道不应该是恒定的，不应该被修剪。有人可以向我解释这段代码有什么问题吗？

使用(* KEEP = "TRUE" *)和(* KEEP_HIERARCHY = "TRUE" *)无效。

Answer 1

更换

tmp[scounter_samp][scounter_bits] <= !input_data[8];

与

case(scounter_samp)
    0: tmp[0][scounter_bits] <= !input_data[8];
    1: tmp[1][scounter_bits] <= !input_data[8];
    2: tmp[2][scounter_bits] <= !input_data[8];
    3: tmp[3][scounter_bits] <= !input_data[8];
    4: tmp[4][scounter_bits] <= !input_data[8];
    5: tmp[5][scounter_bits] <= !input_data[8];
    6: tmp[6][scounter_bits] <= !input_data[8];
    7: tmp[7][scounter_bits] <= !input_data[8];
endcase

解决了这个问题，但我不明白为什么。

FF / Latch修剪

1 个答案: