The great work of Enio hf snoop is now ported into latest version in git

you can find original work here https://github.com/EnioArda/proxmark3

fpga/hi_sniffer.v

@@ -0,0 +1,77 @@
+
+module hi_sniffer(
+    pck0, ck_1356meg, ck_1356megb,
+    pwr_lo, pwr_hi, pwr_oe1, pwr_oe2, pwr_oe3, pwr_oe4,
+    adc_d, adc_clk,
+    ssp_frame, ssp_din, ssp_dout, ssp_clk,
+    cross_hi, cross_lo,
+    dbg,
+    xcorr_is_848, snoop, xcorr_quarter_freq // not used.
+);
+    input pck0, ck_1356meg, ck_1356megb;
+    output pwr_lo, pwr_hi, pwr_oe1, pwr_oe2, pwr_oe3, pwr_oe4;
+    input [7:0] adc_d;
+    output adc_clk;
+    input ssp_dout;
+    output ssp_frame, ssp_din, ssp_clk;
+    input cross_hi, cross_lo;
+    output dbg;
+    input xcorr_is_848, snoop, xcorr_quarter_freq; // not used.
+
+// We are only snooping, all off.
+assign pwr_hi  = 1'b0;// ck_1356megb & (~snoop);
+assign pwr_oe1 = 1'b0;
+assign pwr_oe2 = 1'b0;
+assign pwr_oe3 = 1'b0;
+assign pwr_oe4 = 1'b0;
+
+reg ssp_clk = 1'b0;
+reg ssp_frame;
+reg adc_clk;
+reg [7:0] adc_d_out = 8'd0;
+reg [7:0] ssp_cnt = 8'd0;
+reg [7:0] pck_divider = 8'd0;
+reg ant_lo = 1'b0;
+reg bit_to_send = 1'b0;
+
+always @(ck_1356meg, pck0) // should synthetisize to a mux..
+  begin
+    adc_clk = ck_1356meg;
+    ssp_clk = ~ck_1356meg;
+  end
+
+reg [7:0] cnt_test = 8'd0; // test
+
+always @(posedge pck0)
+begin
+    ant_lo <= 1'b0;
+end
+
+always @(posedge ssp_clk) // ~1356 (hf)
+begin
+  if(ssp_cnt[7:0] == 8'd255) // SSP counter for divides.
+    ssp_cnt[7:0] <= 8'd0;
+  else
+    ssp_cnt <= ssp_cnt + 1;
+
+      if((ssp_cnt[2:0] == 3'b000) && !ant_lo) // To set frame  length
+        begin
+          adc_d_out[7:0] = adc_d; // disable for test
+          bit_to_send = adc_d_out[0];
+          ssp_frame <= 1'b1;
+        end
+      else
+        begin
+          adc_d_out[6:0] = adc_d_out[7:1];
+          adc_d_out[7] = 1'b0; // according to old lf_read.v comment prevents gliches if not set.
+          bit_to_send = adc_d_out[0];
+          ssp_frame <= 1'b0;
+        end
+end
+
+assign ssp_din = bit_to_send && !ant_lo;//bit_to_send && !ant_lo; // && .. not needed i guess?
+
+assign pwr_lo = ant_lo;
+      
+
+endmodule