fix: broken edge detector implementation in hi_iso14443a.v resulted in decreased...

diff --git a/fpga/fpga_hf.bit b/fpga/fpga_hf.bit
index 4910e6ac50d6e3cb405bacee3eef47de443b0147..20fb2bd4401254d899d6273451bfccbd827f562b 100644 (file)
Binary files a/fpga/fpga_hf.bit and b/fpga/fpga_hf.bit differ

diff --git a/fpga/hi_iso14443a.v b/fpga/hi_iso14443a.v
index 46adda12c47c8d5ef5f0860754cfd8d996d468e5..ccb51d8fb307fd46deea03fe72fef9aa194d0a86 100644 (file)
--- a/fpga/hi_iso14443a.v
+++ b/fpga/hi_iso14443a.v
@@ -112,34 +112,26 @@ end
 // for noise reduction and edge detection.
 // store 4 previous samples:
 reg [7:0] input_prev_4, input_prev_3, input_prev_2, input_prev_1;
-// convert to signed signals (and multiply by two for samples at t-4 and t)
-wire signed [10:0] input_prev_4_times_2 = {0, 0, input_prev_4, 0};
-wire signed [10:0] input_prev_3_times_1 = {0, 0, 0, input_prev_3};
-wire signed [10:0] input_prev_1_times_1 = {0, 0, 0, input_prev_1};
-wire signed [10:0] adc_d_times_2 = {0, 0, adc_d, 0}; 
-
-wire signed [10:0] tmp_1, tmp_2;
-wire signed [10:0] adc_d_filtered;
-integer i;
-
-assign tmp_1 = input_prev_4_times_2 + input_prev_3_times_1;
-assign tmp_2 = input_prev_1_times_1 + adc_d_times_2;
-       
+
 always @(negedge adc_clk)
 begin
-       // for (i = 3; i > 0; i = i - 1)
-       // begin
-               // input_shift[i] <= input_shift[i-1];
-       // end
-       // input_shift[0] <= adc_d;
        input_prev_4 <= input_prev_3;
        input_prev_3 <= input_prev_2;
        input_prev_2 <= input_prev_1;
        input_prev_1 <= adc_d;
 end    
 
-// assign adc_d_filtered = (input_shift[3] << 1) + input_shift[2] - input_shift[0] - (adc_d << 1);
-assign adc_d_filtered = tmp_1 - tmp_2;
+// adc_d_filtered = 2*input_prev4 + 1*input_prev3 + 0*input_prev2 - 1*input_prev1 - 2*input
+//                                     = (2*input_prev4 + input_prev3) - (2*input + input_prev1) 
+wire [8:0] input_prev_4_times_2 = input_prev_4 << 1;
+wire [8:0] adc_d_times_2               = adc_d << 1;
+
+wire [9:0] tmp1 = input_prev_4_times_2 + input_prev_3;
+wire [9:0] tmp2 = adc_d_times_2 + input_prev_1;
+
+// convert intermediate signals to signed and calculate the filter output
+wire signed [10:0] adc_d_filtered = {1'b0, tmp1} - {1'b0, tmp2};
+
 
        
 ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
@@ -194,11 +186,13 @@ reg [3:0] mod_detect_reset_time;
 always @(negedge adc_clk)
 begin
        if (mod_type == `READER_LISTEN) 
-       // (our) reader signal changes at t=1, tag response expected n*16+4 ticks later, further delayed by
-       // 3 ticks ADC conversion.
-       // 1 + 4 + 3 = 8
+       // (our) reader signal changes at negedge_cnt[3:0]=9, tag response expected to start n*16+4 ticks later, further delayed by
+       // 3 ticks ADC conversion. The maximum filter output (edge detected) will be detected after subcarrier zero crossing (+7 ticks).
+       // To allow some timing variances, we want to have the maximum filter outputs well within the detection window, i.e.
+       // at mod_detect_reset_time+4 and mod_detect_reset_time+12  (-4 ticks).
+       // 9 + 4 + 3 + 7 - 4  = 19.    19 mod 16 = 3
        begin
-               mod_detect_reset_time <= 4'd8;
+               mod_detect_reset_time <= 4'd4;
        end
        else
        if (mod_type == `SNIFFER)
@@ -207,10 +201,10 @@ begin
                if (~pre_after_hysteresis && after_hysteresis && deep_modulation)
                // reader signal rising edge detected at negedge_cnt[3:0]. This signal had been delayed 
                // 9 ticks by the RF part + 3 ticks by the A/D converter + 1 tick to assign to after_hysteresis.
-               // The tag will respond n*16 + 4 ticks later + 3 ticks A/D converter delay.
-               // - 9 - 3 - 1 + 4 + 3 = -6
+               // Then the same as above.
+               // - 9 - 3 - 1 + 4 + 3 + 7 - 4 = -3
                begin
-                       mod_detect_reset_time <= negedge_cnt[3:0] - 4'd4;
+                       mod_detect_reset_time <= negedge_cnt[3:0] - 4'd3;
                end
        end
 end
@@ -224,12 +218,14 @@ reg signed [10:0] rx_mod_falling_edge_max;
 reg signed [10:0] rx_mod_rising_edge_max;
 reg curbit;
 
+`define EDGE_DETECT_THRESHOLD  5
+
 always @(negedge adc_clk)
 begin
        if(negedge_cnt[3:0] == mod_detect_reset_time)
        begin
                // detect modulation signal: if modulating, there must have been a falling AND a rising edge
-               if (rx_mod_falling_edge_max > 5 && rx_mod_rising_edge_max > 5)
+               if ((rx_mod_falling_edge_max > `EDGE_DETECT_THRESHOLD) && (rx_mod_rising_edge_max < -`EDGE_DETECT_THRESHOLD))
                                curbit <= 1'b1; // modulation
                        else
                                curbit <= 1'b0; // no modulation
@@ -246,8 +242,8 @@ begin
                end
                else
                begin
-                       if (-adc_d_filtered > rx_mod_rising_edge_max)
-                               rx_mod_rising_edge_max <= -adc_d_filtered;
+                       if (adc_d_filtered < rx_mod_rising_edge_max)
+                               rx_mod_rising_edge_max <= adc_d_filtered;
                end
        end
 
@@ -273,7 +269,7 @@ end
 
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
-// PM3 -> Tag:
+// PM3 -> Reader:
 // a delay line to ensure that we send the (emulated) tag's answer at the correct time according to ISO14443-3
 reg [31:0] mod_sig_buf;
 reg [4:0] mod_sig_ptr;
@@ -297,7 +293,7 @@ end
 
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
-// PM3 -> Tag, internal timing:
+// PM3 -> Reader, internal timing:
 // a timer for the 1172 cycles fdt (Frame Delay Time). Start the timer with a rising edge of the reader's signal.
 // set fdt_elapsed when we no longer need to delay data. Set fdt_indicator when we can start sending data.
 // Note: the FPGA only takes care for the 1172 delay. To achieve an additional 1236-1172=64 ticks delay, the ARM must send
@@ -477,11 +473,10 @@ end
 
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
-// FPGA -> ARM communication:
+// FPGA <-> ARM communication:
 // generate a ssp clock and ssp frame signal for the synchronous transfer from/to the ARM
 reg ssp_clk;
 reg ssp_frame;
-reg [2:0] ssp_frame_counter;
 
 always @(negedge adc_clk)
 begin