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Diffstat (limited to 'fpga/usrp2/sdr_lib/hb/halfband_decim.v')
| -rw-r--r-- | fpga/usrp2/sdr_lib/hb/halfband_decim.v | 163 |
1 files changed, 163 insertions, 0 deletions
diff --git a/fpga/usrp2/sdr_lib/hb/halfband_decim.v b/fpga/usrp2/sdr_lib/hb/halfband_decim.v new file mode 100644 index 000000000..dff4d902c --- /dev/null +++ b/fpga/usrp2/sdr_lib/hb/halfband_decim.v @@ -0,0 +1,163 @@ +/* -*- verilog -*- + * + * USRP - Universal Software Radio Peripheral + * + * Copyright (C) 2005 Matt Ettus + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License as published by + * the Free Software Foundation; either version 2 of the License, or + * (at your option) any later version. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with this program; if not, write to the Free Software + * Foundation, Inc., 51 Franklin Street, Boston, MA 02110-1301 USA + */ + +/* + * This implements a 31-tap halfband filter that decimates by two. + * The coefficients are symmetric, and with the exception of the middle tap, + * every other coefficient is zero. The middle section of taps looks like this: + * + * ..., -1468, 0, 2950, 0, -6158, 0, 20585, 32768, 20585, 0, -6158, 0, 2950, 0, -1468, ... + * | + * middle tap -------+ + * + * See coeff_rom.v for the full set. The taps are scaled relative to 32768, + * thus the middle tap equals 1.0. Not counting the middle tap, there are 8 + * non-zero taps on each side, and they are symmetric. A naive implementation + * requires a mulitply for each non-zero tap. Because of symmetry, we can + * replace 2 multiplies with 1 add and 1 multiply. Thus, to compute each output + * sample, we need to perform 8 multiplications. Since the middle tap is 1.0, + * we just add the corresponding delay line value. + * + * About timing: We implement this with a single multiplier, so it takes + * 8 cycles to compute a single output. However, since we're decimating by two + * we can accept a new input value every 4 cycles. strobe_in is asserted when + * there's a new input sample available. Depending on the overall decimation + * rate, strobe_in may be asserted less frequently than once every 4 clocks. + * On the output side, we assert strobe_out when output contains a new sample. + * + * Implementation: Every time strobe_in is asserted we store the new data into + * the delay line. We split the delay line into two components, one for the + * even samples, and one for the odd samples. ram16_odd is the delay line for + * the odd samples. This ram is written on each odd assertion of strobe_in, and + * is read on each clock when we're computing the dot product. ram16_even is + * similar, although because it holds the even samples we must be able to read + * two samples from different addresses at the same time, while writing the incoming + * even samples. Thus it's "triple-ported". + */ + +module halfband_decim + (input clock, input reset, input enable, input strobe_in, output wire strobe_out, + input wire [15:0] data_in, output reg [15:0] data_out,output wire [15:0] debugctrl); + + reg [3:0] rd_addr1; + reg [3:0] rd_addr2; + reg [3:0] phase; + reg [3:0] base_addr; + + wire signed [15:0] mac_out,middle_data, sum, coeff; + wire signed [30:0] product; + wire signed [33:0] sum_even; + wire clear; + reg store_odd; + + always @(posedge clock) + if(reset) + store_odd <= #1 1'b0; + else + if(strobe_in) + store_odd <= #1 ~store_odd; + + wire start = strobe_in & store_odd; + always @(posedge clock) + if(reset) + base_addr <= #1 4'd0; + else if(start) + base_addr <= #1 base_addr + 4'd1; + + always @(posedge clock) + if(reset) + phase <= #1 4'd8; + else if (start) + phase <= #1 4'd0; + else if(phase != 4'd8) + phase <= #1 phase + 4'd1; + + reg start_d1,start_d2,start_d3,start_d4,start_d5,start_d6,start_d7,start_d8,start_d9,start_dA,start_dB,start_dC,start_dD; + always @(posedge clock) + begin + start_d1 <= #1 start; + start_d2 <= #1 start_d1; + start_d3 <= #1 start_d2; + start_d4 <= #1 start_d3; + start_d5 <= #1 start_d4; + start_d6 <= #1 start_d5; + start_d7 <= #1 start_d6; + start_d8 <= #1 start_d7; + start_d9 <= #1 start_d8; + start_dA <= #1 start_d9; + start_dB <= #1 start_dA; + start_dC <= #1 start_dB; + start_dD <= #1 start_dC; + end // always @ (posedge clock) + + reg mult_en, mult_en_pre; + always @(posedge clock) + begin + mult_en_pre <= #1 phase!=8; + mult_en <= #1 mult_en_pre; + end + + assign clear = start_d4; // was dC + wire latch_result = start_d4; // was dC + assign strobe_out = start_d5; // was dD + wire acc_en; + + always @* + case(phase[2:0]) + 3'd0 : begin rd_addr1 = base_addr + 4'd0; rd_addr2 = base_addr + 4'd15; end + 3'd1 : begin rd_addr1 = base_addr + 4'd1; rd_addr2 = base_addr + 4'd14; end + 3'd2 : begin rd_addr1 = base_addr + 4'd2; rd_addr2 = base_addr + 4'd13; end + 3'd3 : begin rd_addr1 = base_addr + 4'd3; rd_addr2 = base_addr + 4'd12; end + 3'd4 : begin rd_addr1 = base_addr + 4'd4; rd_addr2 = base_addr + 4'd11; end + 3'd5 : begin rd_addr1 = base_addr + 4'd5; rd_addr2 = base_addr + 4'd10; end + 3'd6 : begin rd_addr1 = base_addr + 4'd6; rd_addr2 = base_addr + 4'd9; end + 3'd7 : begin rd_addr1 = base_addr + 4'd7; rd_addr2 = base_addr + 4'd8; end + default: begin rd_addr1 = base_addr + 4'd0; rd_addr2 = base_addr + 4'd15; end + endcase // case(phase) + + coeff_rom coeff_rom (.clock(clock),.addr(phase[2:0]-3'd1),.data(coeff)); + + ram16_2sum ram16_even (.clock(clock),.write(strobe_in & ~store_odd), + .wr_addr(base_addr),.wr_data(data_in), + .rd_addr1(rd_addr1),.rd_addr2(rd_addr2), + .sum(sum)); + + ram16 ram16_odd (.clock(clock),.write(strobe_in & store_odd), // Holds middle items + .wr_addr(base_addr),.wr_data(data_in), + //.rd_addr(base_addr+4'd7),.rd_data(middle_data)); + .rd_addr(base_addr+4'd6),.rd_data(middle_data)); + + mult mult(.clock(clock),.x(coeff),.y(sum),.product(product),.enable_in(mult_en),.enable_out(acc_en)); + + acc acc(.clock(clock),.reset(reset),.enable_in(acc_en),.enable_out(), + .clear(clear),.addend(product),.sum(sum_even)); + + wire signed [33:0] dout = sum_even + {{4{middle_data[15]}},middle_data,14'b0}; // We already divided product by 2!!!! + + always @(posedge clock) + if(reset) + data_out <= #1 16'd0; + else if(latch_result) + data_out <= #1 dout[30:15] + (dout[33]& |dout[14:0]); + + assign debugctrl = { clock,reset,acc_en,mult_en,clear,latch_result,store_odd,strobe_in,strobe_out,phase}; + +endmodule // halfband_decim |