source: trunk/MultiChannelUSB/uwt_bior31.v@ 46

module uwt_bior31
        #(
                parameter       L       =       1 // transform level
        )
        (
                input   wire                    clk, reset,
                input   wire    [31:0]  x,
                output  wire    [31:0]  d,
                output  wire    [31:0]  a,
                output  wire    [31:0]  peak,
                output  wire    [1:0]   flag
        );

        localparam      index1          =       1 << (L - 1);
        localparam      index2          =       2 << (L - 1);
        localparam      index3          =       3 << (L - 1);
        localparam      peak_index      =       ((3 << (L - 1)) + 1) >> 1;
        localparam      peak_shift      =       ((L - 1) << 1) + (L - 1);
        localparam      zero            =       32'h80000000;
        
        // Tapped delay line
        reg             [31:0]  tap [index3:0];
        
        reg             [31:0]  d_reg, d_next;
        reg             [31:0]  a_reg, a_next;
        reg             [31:0]  peak_reg, peak_next;

        reg             [1:0]   flag_reg;

        integer                 i;
        
        always @(posedge clk, posedge reset)
        begin
                if (reset)
                begin
                        d_reg <= 0;
                        a_reg <= 0;
                        peak_reg <= 0;
                        flag_reg <= 0;

                        for(i = 0; i <= index3; i = i + 1)
                        begin
                                tap[i] <= 0;
                        end
                end
                else
                begin
                        d_reg <= d_next;
                        a_reg <= a_next;
                        peak_reg <= peak_next;
                        
                        flag_reg[0] <= (d_reg > zero) & (d_next <= zero);
                        flag_reg[1] <= (d_reg < zero) & (d_next >= zero);
        
                        // Tapped delay line: shift one
                        for(i = 0; i < index3; i = i + 1)
                        begin
                                tap[i+1] <= tap[i];
                        end
                        
                        // Input in register 0
                        tap[0] <= x;
                end
        end
        
        always @*
        begin
                // Compute d and a with the filter coefficients.
                // The coefficients are [1, 3, -3, -1] and [1, 3, 3, 1]

                d_next = zero - (tap[index3])
                           - (tap[index2] << 1) - tap[index2]
                           + (tap[index1] << 1) + tap[index1]
                           + (tap[0]);
                
                a_next = (tap[index3])
                           + (tap[index2] << 1) + tap[index2]
                           + (tap[index1] << 1) + tap[index1]
                           + (tap[0]);

                peak_next = (tap[peak_index] >> peak_shift);
        end

        // output logic
        assign  d               =       d_reg;
        assign  a               =       a_reg;
        assign  peak    =       peak_reg;
        assign  flag    =       flag_reg;

endmodule