Foreword:

This column aims to record high-frequency pen interview hand-torn code questions for digital front-end autumn recruits. All articles in this column provide principle analysis, codes and waveforms, and all codes have been verified by myself.

The directory is as follows:

...Continually updated

For more hand-tearing code questions, you can go to the digital IC hand-tearing code--question bank

Table of contents

topic description

problem solving ideas

the code

testbench

waveform

topic description

Use HDL language to realize the interleaver in a way to save chip area. Assume that the input datain order is 1, 2, 3, ... 63, the input enable is datain_ena, and the output order after the interleaver is required to be 1, 10, 19, 28, 37, 46, 55, 2, 11, ...

That is, rows and columns are interleaved, in the order of rows and out in the order of columns, and the input and output data change according to the clock edge. When implementing, you can define ram and use it yourself.

1 2 3 4 5 6 7 8 9

10 11 12 13 14 15 16 17 18

19 20 21 22 23 24 25 26 27

28 29 30 31 32 33 34 35 36

37 38 39 40 41 42 43 44 45

46 47 48 49 50 51 52 53 54

55 56 57 58 59 60 61 62 63

problem solving ideas

After reading the title, I know that input 64 numbers, save them into a 7*9 matrix, and then output them in columns. To change the meaning of the question, the so-called interleaver in the title here actually realizes the function of transposing a matrix. The matrix input by row is output by column, and data write and read are effectively enabled.

the code

module matrix_trans(
    input               clk         ,
    input               rstn        ,
    input       [5:0]   datain      ,
    input               datain_ena  ,

    output      [5:0]   dataout     ,
    output  reg         dataout_ena 
);

reg [5:0] ram [62:0];  //63 numbers
reg [5:0] addr_wr,addr_rd;

// write data
always @(posedge clk)begin
    if(!rstn)begin
        addr_wr <= 6'd0;
    end
    else if(datain_ena && addr_wr < 62)begin
        addr_wr <= addr_wr + 1'b1; 
    end
    else if(datain_ena && addr_wr ==62)begin
        addr_wr <= 6'd1;
    end
end

always @(posedge clk)begin
    if(datain_ena)begin
        ram[addr_wr] <= datain;
    end
end

// read data
always @(posedge clk)begin
    if(!rstn)begin
        dataout_ena <= 1'b0;
    end
    else if(addr_rd == 6'd62)begin
        dataout_ena <= 1'b0;
    end
    else if(addr_wr == 6'd62 && datain_ena == 1'b1)begin
        dataout_ena <= 1'b1;
    end 
end

always @(posedge clk)begin
    if(!rstn)begin
        addr_rd     <= 6'd0;
    end
    else if(dataout_ena==1'b1 && addr_rd < 62)begin
        addr_rd     <= addr_rd + 1'b1;
    end
    else if(dataout_ena==1'b1 && addr_rd == 62)begin
        addr_rd     <= 6'd0;
    end
end
// 9*7 
// 0=0,1=9,2=18,3=27,4=36,5=45,6=54, 7=1
assign dataout = ram[((addr_rd)%7)*9+addr_rd/7];

endmodule

testbench

module matrix_trans_tb();
reg clk,rstn;
reg [5:0] datain;
reg datain_ena;

wire [5:0] dataout;
wire dataout_ena;

always #5 clk = ~clk;

initial begin
    clk <= 1'b0;
    rstn <= 1'b0;
    #20
    rstn <= 1'b1;
    #20
    datain <= 6'd1;
    #20
    datain_ena <= 1'b1;
    repeat(63)begin
        @(posedge clk)begin
            datain <= datain + 1'b1;
        end
    end
    datain_ena <= 1'b0;
    #2000
    $finish();
end

initial begin
    forever begin
        @(posedge clk)begin
            if(dataout_ena == 1'b1)begin
                $display("dataout = %d", dataout);
            end
        end
    end
end

//dump fsdb
initial begin
    $fsdbDumpfile("matrix_trans.fsdb");
    $fsdbDumpvars(0);
end

matrix_trans u_matrix_trans(
    .clk            (clk)           ,
    .rstn           (rstn)          ,
    
    .datain         (datain)        ,
    .datain_ena     (datain_ena)    ,

    .dataout        (dataout)       ,
    .dataout_ena    (dataout_ena)
);

endmodule

waveform

We have completed writing 63 numbers in the form of matrix rows, and reading 63 numbers in the form of matrix columns. The read results are shown in the figure:

The output is correct.

For more hand-tearing code questions, you can go to the digital IC hand-tearing code--question bank

Digital IC hand tearing code-XX company written test questions (interleaver/matrix transpose)

topic description

problem solving ideas

the code

testbench

waveform

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