1PPS Signal on USRP1

GNU Radio
1

I’d like to take in a 1PPS signal on the USRP1, and, using the inband
FPGA
firmware, trigger a reset of the timestamp on the rising edge of every
1PPS
pulse to get a rough idea of timing. From reading the documentation, I
know
that my max input voltage cannot be higher than 3.3V, so I’ve got that
covered, but I can’t seem to get the verilog code to work. I’ve
modified
the verilog code to add the following lines to the top level code:

    // Master timestamp counter
    reg [31:0] timestamp_counter;

    wire

ts_io_reset;
//
<-- NEW LINE
assign ts_io_reset = io_rx_a[0];
// <-- NEW LINE
always @ (posedge clk64 or posedge ts_io_reset) begin // <–
MODIFIED
if (ts_io_reset)
// <-- NEW LINE
timestamp_counter <=
32’d0; // <-- NEW LINE
else if (tx_dsp_reset | rx_dsp_reset) //FIXME:
does
it make sense for rx/tx to reset independently?
timestamp_counter <= 32’d0;
else
timestamp_counter <= timestamp_counter + 32’d1;
end

Nothing happens when I apply a test input to input 0 of the basic rx
board
(I am also polling the io from software with read_io, and I see the
input
switching). I am new to verilog, but for the life of me I can’t figure
out
what I’m doing wrong here.

I am using a basic_rx and a basic_tx on side 0 of a USRP1.

Thanks,
Mike