我实际上正在研究Jingjing Shi提供的802.11a协议
该代码可以在github https://github.com/jhshi/openofdm/tree/master/verilog中找到。
在sync_long.v中，我不明白为什么在检测到LTS2之后且在执行fft之前为何存在in_raddr = addr1-16。
addr1表示检测到LTS1的样本。理想情况下，应从addr1执行fft。
但是在这里，fft是从addr1-16执行的。为什么会这样？
input clock,
input reset,
input enable,
input set_stb,
input [7:0] set_addr,
input [31:0] set_data,
input [31:0] sample_in,
input sample_in_strobe,
input signed [31:0] phase_offset,
input short_gi,
output [`ROTATE_LUT_LEN_SHIFT-1:0] rot_addr,
input [31:0] rot_data,
output [31:0] metric,
output metric_stb,
output reg long_preamble_detected,
output reg [31:0] sample_out,
output reg sample_out_strobe,
output reg [2:0] state
);
`include "common_params.v"
localparam IN_BUF_LEN_SHIFT = 8;
localparam NUM_STS_TAIL = 32;
reg [15:0] in_offset;
reg [IN_BUF_LEN_SHIFT-1:0] in_waddr;
reg [IN_BUF_LEN_SHIFT-1:0] in_raddr;
wire [IN_BUF_LEN_SHIFT-1:0] gi_skip = short_gi? 9: 17;
reg signed [31:0] num_input_produced;
reg signed [31:0] num_input_consumed;
reg signed [31:0] num_input_avail;
reg [2:0] mult_stage;
reg [1:0] sum_stage;
reg mult_strobe;
wire signed [31:0] stage_sum_i;
wire signed [31:0] stage_sum_q;
wire stage_sum_stb;
reg signed [31:0] sum_i;
reg signed [31:0] sum_q;
reg sum_stb;
reg signed [31:0] phase_correction;
reg signed [31:0] next_phase_correction;
complex_to_mag #(.DATA_WIDTH(32)) sum_mag_inst (
.clock(clock),
.enable(enable),
.reset(reset),
.i(sum_i),
.q(sum_q),
.input_strobe(sum_stb),
.mag(metric),
.mag_stb(metric_stb)
);
reg [31:0] metric_max1;
reg [(IN_BUF_LEN_SHIFT-1):0] addr1;
reg [31:0] metric_max2;
reg [(IN_BUF_LEN_SHIFT-1):0] addr2;
reg [15:0] gap;
reg [31:0] cross_corr_buf[0:15];
reg [31:0] stage_X0;
reg [31:0] stage_X1;
reg [31:0] stage_X2;
reg [31:0] stage_X3;
reg [31:0] stage_Y0;
reg [31:0] stage_Y1;
reg [31:0] stage_Y2;
reg [31:0] stage_Y3;
stage_mult stage_mult_inst (
.clock(clock),
.enable(enable),
.reset(reset),
.X0(stage_X0[31:16]),
.X1(stage_X0[15:0]),
.X2(stage_X1[31:16]),
.X3(stage_X1[15:0]),
.X4(stage_X2[31:16]),
.X5(stage_X2[15:0]),
.X6(stage_X3[31:16]),
.X7(stage_X3[15:0]),
.Y0(stage_Y0[31:16]),
.Y1(stage_Y0[15:0]),
.Y2(stage_Y1[31:16]),
.Y3(stage_Y1[15:0]),
.Y4(stage_Y2[31:16]),
.Y5(stage_Y2[15:0]),
.Y6(stage_Y3[31:16]),
.Y7(stage_Y3[15:0]),
.input_strobe(mult_strobe),
.sum({stage_sum_i, stage_sum_q}),
.output_strobe(stage_sum_stb)
);
localparam S_SKIPPING = 0;
localparam S_WAIT_FOR_FIRST_PEAK = 1;
localparam S_WAIT_FOR_SECOND_PEAK = 2;
localparam S_IDLE = 3;
localparam S_FFT = 4;
reg fft_start;
wire fft_start_delayed;
wire fft_in_stb;
reg fft_loading;
wire signed [15:0] fft_in_re;
wire signed [15:0] fft_in_im;
wire [22:0] fft_out_re;
wire [22:0] fft_out_im;
wire fft_ready;
wire fft_done;
wire fft_busy;
wire fft_valid;
wire [31:0] fft_out = {fft_out_re[22:7], fft_out_im[22:7]};
wire signed [15:0] raw_i;
wire signed [15:0] raw_q;
reg raw_stb;
ram_2port #(.DWIDTH(32), .AWIDTH(IN_BUF_LEN_SHIFT)) in_buf (
.clka(clock),
.ena(1),
.wea(sample_in_strobe),
.addra(in_waddr),
.dia(sample_in),
.doa(),
.clkb(clock),
.enb(fft_start | fft_loading),
.web(1'b0),
.addrb(in_raddr),
.dib(32'hFFFF),
.dob({raw_i, raw_q})
);
rotate rotate_inst (
.clock(clock),
.enable(enable),
.reset(reset),
.in_i(raw_i),
.in_q(raw_q),
.phase(phase_correction),
.input_strobe(raw_stb),
.rot_addr(rot_addr),
.rot_data(rot_data),
.out_i(fft_in_re),
.out_q(fft_in_im),
.output_strobe(fft_in_stb)
);
delayT #(.DATA_WIDTH(1), .DELAY(9)) fft_delay_inst (
.clock(clock),
.reset(reset),
.data_in(fft_start),
.data_out(fft_start_delayed)
);
xfft_v7_1 dft_inst (
.clk(clock),
.fwd_inv(1),
.start(fft_start_delayed),
.fwd_inv_we(1),
.xn_re(fft_in_re),
.xn_im(fft_in_im),
.xk_re(fft_out_re),
.xk_im(fft_out_im),
.rfd(fft_ready),
.done(fft_done),
.busy(fft_busy),
.dv(fft_valid)
);
reg [15:0] num_sample;
reg [15:0] num_ofdm_symbol;
integer i;
integer j;
always @(posedge clock) begin
if (reset) begin
for (j = 0; j < 16; j= j+1) begin
cross_corr_buf[j] <= 0;
end
do_clear();
state <= S_SKIPPING;
end else if (enable) begin
if (sample_in_strobe && state != S_SKIPPING) begin
in_waddr <= in_waddr + 1;
num_input_produced <= num_input_produced + 1;
end
num_input_avail <= num_input_produced - num_input_consumed;
case(state)
S_SKIPPING: begin
// skip the tail of short preamble
if (num_sample >= NUM_STS_TAIL) begin
num_sample <= 0;
state <= S_WAIT_FOR_FIRST_PEAK;
end else if (sample_in_strobe) begin
num_sample <= num_sample + 1;
end
end
S_WAIT_FOR_FIRST_PEAK: begin
do_mult();
if (metric_stb && (metric > metric_max1)) begin
metric_max1 <= metric;
addr1 <= in_raddr - 1;
end
if (num_sample >= 64) begin
num_sample <= 0;
addr2 <= 0;
state <= S_WAIT_FOR_SECOND_PEAK;
end else if (metric_stb) begin
num_sample <= num_sample + 1;
end
end
S_WAIT_FOR_SECOND_PEAK: begin
do_mult();
if (metric_stb && (metric > metric_max2)) begin
metric_max2 <= metric;
addr2 <= in_raddr - 1;
end
gap <= addr2 - addr1;
if (num_sample >= 64) begin
`ifdef DEBUG_PRINT
$display("PEAK GAP: %d (%d - %d)", gap, addr2, addr1);
$display("PHASE OFFSET: %d", phase_offset);
`endif
if (gap > 62 && gap < 66) begin
long_preamble_detected <= 1;
num_sample <= 0;
mult_strobe <= 0;
sum_stb <= 0;
// offset it by the length of cross correlation buffer
// size
in_raddr <= addr1 - 16;
num_input_consumed <= addr1 - 16;
in_offset <= 0;
num_ofdm_symbol <= 0;
phase_correction <= 0;
next_phase_correction <= phase_offset;
state <= S_FFT;
end else begin
state <= S_IDLE;
end
end else if (metric_stb) begin
num_sample <= num_sample + 1;
end
end
S_FFT: begin
if (long_preamble_detected) begin
`ifdef DEBUG_PRINT
$display("Long preamble detected");
`endif
long_preamble_detected <= 0;
end
if (~fft_loading && num_input_avail > 64) begin
fft_start <= 1;
in_offset <= 0;
end
if (fft_start) begin
fft_start <= 0;
fft_loading <= 1;
end
raw_stb <= fft_start | fft_loading;
if (raw_stb) begin
if (phase_offset > 0) begin
if (next_phase_correction > PI) begin
phase_correction <= next_phase_correction - DOUBLE_PI;
next_phase_correction <= next_phase_correction + phase_offset - DOUBLE_PI;
end else begin
phase_correction <= next_phase_correction;
next_phase_correction <= next_phase_correction + phase_offset;
end
end else begin
if (next_phase_correction < -PI) begin
phase_correction <= next_phase_correction + DOUBLE_PI;
phase_correction <= next_phase_correction + DOUBLE_PI + phase_offset;
end else begin
phase_correction <= next_phase_correction;
phase_correction <= next_phase_correction + phase_offset;
end
end
end
if (fft_start | fft_loading) begin
in_offset <= in_offset + 1;
if (in_offset == 63) begin
fft_loading <= 0;
num_ofdm_symbol <= num_ofdm_symbol + 1;
if (num_ofdm_symbol > 0) begin
// skip the Guard Interval for data symbols
in_raddr <= in_raddr + gi_skip;
num_input_consumed <= num_input_consumed + gi_skip;
end else begin
in_raddr <= in_raddr + 1;
num_input_consumed <= num_input_consumed + 1;
end
end else begin
in_raddr <= in_raddr + 1;
num_input_consumed <= num_input_consumed + 1;
end
end
sample_out_strobe <= fft_valid;
sample_out <= fft_out;
end
S_IDLE: begin
end
default: begin
state <= S_WAIT_FOR_FIRST_PEAK;
end
endcase
end else begin
sample_out_strobe <= 0;
end
end
integer do_mult_i;
task do_mult; begin
// cross correlation of the first 16 samples of LTS
if (sample_in_strobe) begin
cross_corr_buf[15] <= sample_in;
for (do_mult_i = 0; do_mult_i < 15; do_mult_i = do_mult_i+1) begin
cross_corr_buf[do_mult_i] <= cross_corr_buf[do_mult_i+1];
end
sum_stage <= 0;
sum_i <= 0;
sum_q <= 0;
sum_stb <= 0;
stage_X0 <= cross_corr_buf[1];
stage_X1 <= cross_corr_buf[2];
stage_X2 <= cross_corr_buf[3];
stage_X3 <= cross_corr_buf[4];
stage_Y0[31:16] <= 156;
stage_Y0[15:0] <= 0;
stage_Y1[31:16] <= -5;
stage_Y1[15:0] <= 120;
stage_Y2[31:16] <= 40;
stage_Y2[15:0] <= 111;
stage_Y3[31:16] <= 97;
stage_Y3[15:0] <= -83;
mult_strobe <= 1;
mult_stage <= 1;
end
if (mult_stage == 1) begin
stage_X0 <= cross_corr_buf[4];
stage_X1 <= cross_corr_buf[5];
stage_X2 <= cross_corr_buf[6];
stage_X3 <= cross_corr_buf[7];
stage_Y0[31:16] <= 21;
stage_Y0[15:0] <= -28;
stage_Y1[31:16] <= 60;
stage_Y1[15:0] <= 88;
stage_Y2[31:16] <= -115;
stage_Y2[15:0] <= 55;
stage_Y3[31:16] <= -38;
stage_Y3[15:0] <= 106;
mult_stage <= 2;
end else if (mult_stage == 2) begin
stage_X0 <= cross_corr_buf[8];
stage_X1 <= cross_corr_buf[9];
stage_X2 <= cross_corr_buf[10];
stage_X3 <= cross_corr_buf[11];
stage_Y0[31:16] <= 98;
stage_Y0[15:0] <= 26;
stage_Y1[31:16] <= 53;
stage_Y1[15:0] <= -4;
stage_Y2[31:16] <= 1;
stage_Y2[15:0] <= 115;
stage_Y3[31:16] <= -137;
stage_Y3[15:0] <= 47;
mult_stage <= 3;
end else if (mult_stage == 3) begin
stage_X0 <= cross_corr_buf[12];
stage_X1 <= cross_corr_buf[13];
stage_X2 <= cross_corr_buf[14];
stage_X3 <= cross_corr_buf[15];
stage_Y0[31:16] <= 24;
stage_Y0[15:0] <= 59;
stage_Y1[31:16] <= 59;
stage_Y1[15:0] <= 15;
stage_Y2[31:16] <= -22;
stage_Y2[15:0] <= -161;
stage_Y3[31:16] <= 119;
stage_Y3[15:0] <= 4;
mult_stage <= 4;
end else if (mult_stage == 4) begin
mult_stage <= 0;
mult_strobe <= 0;
in_raddr <= in_raddr + 1;
num_input_consumed <= num_input_consumed + 1;
end
if (stage_sum_stb) begin
sum_stage <= sum_stage + 1;
sum_i <= sum_i + stage_sum_i;
sum_q <= sum_q + stage_sum_q;
if (sum_stage == 3) begin
sum_stb <= 1;
end
end else begin
sum_stb <= 0;
sum_i <= 0;
sum_q <= 0;
end
end
endtask
task do_clear; begin
gap <= 0;
in_waddr <= 0;
in_raddr <= 0;
in_offset <= 0;
num_input_produced <= 0;
num_input_consumed <= 0;
num_input_avail <= 0;
phase_correction <= 0;
next_phase_correction <= 0;
raw_stb <= 0;
sum_i <= 0;
sum_q <= 0;
sum_stb <= 0;
sum_stage <= 0;
mult_strobe <= 0;
metric_max1 <= 0;
addr1 <= 0;
metric_max2 <= 0;
addr2 <= 0;
mult_stage <= 0;
long_preamble_detected <= 0;
num_sample <= 0;
num_ofdm_symbol <= 0;
fft_start <= 0;
fft_loading <= 0;
sample_out_strobe <= 0;
sample_out <= 0;
stage_X0 <= 0;
stage_X1 <= 0;
stage_X2 <= 0;
stage_X3 <= 0;
stage_Y0 <= 0;
stage_Y1 <= 0;
stage_Y2 <= 0;
stage_Y3 <= 0;
end
endtask
endmodule