--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/fpga/sniffer-pps/sniff_rx.v	Tue Aug 29 20:05:23 2023 +0000
@@ -0,0 +1,62 @@
+/*
+ * This Verilog module captures the ISO 7816-3 character sniffing receiver.
+ */
+
+module sniff_rx (IntClk, SIM_RST_sync, SIM_CLK_sync, SIM_IO_sync,
+		 Rx_strobe, Rx_error, Rx_char, Rx_start_bit, Rx_parity_bit);
+
+input IntClk;
+input SIM_RST_sync, SIM_CLK_sync, SIM_IO_sync;
+output Rx_strobe, Rx_error;
+output [7:0] Rx_char;
+output Rx_start_bit, Rx_parity_bit;
+
+wire SIM_CLK_edge;
+
+clk_edge clk_edge (IntClk, SIM_CLK_sync, SIM_CLK_edge);
+
+wire [9:0] etu_0p5, etu_1p0, etu_1p5;
+
+/* Fi/Di=372 only for now */
+assign etu_0p5 = 10'd185;
+assign etu_1p0 = 10'd371;
+assign etu_1p5 = 10'd557;
+
+reg rx_active;
+reg [9:0] clk_count;
+reg [3:0] bit_count;
+reg [9:0] shift_reg;
+
+always @(posedge IntClk)
+	if (!SIM_RST_sync)
+		rx_active <= 1'b0;
+	else if (!rx_active && !SIM_IO_sync)
+	    begin
+		rx_active <= 1'b1;
+		clk_count <= etu_0p5;
+		bit_count <= 4'd0;
+	    end
+	else if (rx_active && SIM_CLK_edge)
+	    begin
+		if (clk_count != 10'd0)
+			clk_count <= clk_count - 10'd1;
+		else begin
+			shift_reg <= {SIM_IO_sync,shift_reg[9:1]};
+			bit_count <= bit_count + 4'd1;
+			if (bit_count == 4'd9)
+				clk_count <= etu_1p5;
+			else
+				clk_count <= etu_1p0;
+			if (bit_count == 4'd10)
+				rx_active <= 1'b0;
+		end
+	end
+
+assign Rx_strobe = rx_active && SIM_CLK_edge && clk_count == 10'd0 &&
+		   bit_count == 4'd10;
+assign Rx_error = Rx_strobe && !SIM_IO_sync;
+assign Rx_char = shift_reg[8:1];
+assign Rx_start_bit = shift_reg[0];
+assign Rx_parity_bit = shift_reg[9];
+
+endmodule