remove unnecessary code from fpga test

verilog/rtl/fpga/fpga_pins.pcf

diff --git a/verilog/rtl/fpga/fpga_pins.pcf b/verilog/rtl/fpga/fpga_pins.pcf
index e3054f5..16d878e 100644
--- a/verilog/rtl/fpga/fpga_pins.pcf
+++ b/verilog/rtl/fpga/fpga_pins.pcf
@@ -7,5 +7,4 @@
 set_io usb_p B4
 set_io uart_tx A2
 set_io uart_rx A1
-set_io led B3
 set_io clk B2

verilog/rtl/fpga/fpga_top.v

diff --git a/verilog/rtl/fpga/fpga_top.v b/verilog/rtl/fpga/fpga_top.v
index 08a615b..df4e986 100644
--- a/verilog/rtl/fpga/fpga_top.v
+++ b/verilog/rtl/fpga/fpga_top.v
@@ -1,6 +1,5 @@
 module fpga_top (
    input  clk, // 16MHz Clock
-   output led, // User LED ON=1, OFF=0
    input  uart_rx, // uart in
    output uart_tx, // uart out
    inout  usb_p, // USB+
@@ -13,15 +12,12 @@
    localparam c_UART_SPEED      = 115200;
    localparam c_CLKS_PER_BYTE   = (c_CLOCK_MHZ*1000000+c_UART_SPEED*8-1)/(c_UART_SPEED*8);
 
-   wire             clk_pll;
-   wire             lock;
+   wire clk_pll;
+   pll pll48( .clock_in(clk), .clock_out(clk_pll) );
 
-   wire             dp_pu;
-   wire             dp_rx;
-   wire             dn_rx;
-   wire             dp_tx;
-   wire             dn_tx;
-   wire             tx_en;
+   reg [5:0] reset_cnt = 0;
+   wire rstn = &reset_cnt;
+   always @(posedge clk_pll) reset_cnt <= reset_cnt + !rstn;
 
    wire             in_ready;
    wire [7:0]       in_data;
@@ -30,21 +26,6 @@
    wire [7:0]       out_data;
    wire             out_valid;
 
-   pll pll48( .clock_in(clk), .clock_out(clk_pll), .locked( lock ) );
-
-   assign led = 1'b1;
-
-   reg [1:0]        rstn_sync;
-   wire             rstn;
-   assign rstn = rstn_sync[0];
-   always @(posedge clk_pll or negedge lock) begin
-      if (~lock) begin
-         rstn_sync <= 2'd0;
-      end else begin
-         rstn_sync <= {1'b1, rstn_sync[1]};
-      end
-   end
-
    uart # (
       .DATA_WIDTH(8)
    ) u_uart (
@@ -66,6 +47,21 @@
       .prescale(c_CLKS_PER_BYTE)
    );
 
+   wire             dp_pu;
+   wire             dp_rx;
+   wire             dn_rx;
+   wire             dp_tx;
+   wire             dn_tx;
+   wire             tx_en;
+
+   assign usb_p = tx_en ? dp_tx : 1'bz;
+   assign dp_rx = usb_p;
+
+   assign usb_n = tx_en ? dn_tx : 1'bz;
+   assign dn_rx = usb_n;
+
+   assign usb_pu = dp_pu;
+
    usb_cdc #(
       .VENDORID(16'h1D50),
       .PRODUCTID(16'h6130)
@@ -84,9 +80,6 @@
       .in_valid_i(in_valid),
       .in_ready_o(in_ready),
 
-      .frame_o(),
-      .configured_o(),
-
       .dp_pu_o(dp_pu),
       .tx_en_o(tx_en),
       .dp_tx_o(dp_tx),
@@ -95,50 +88,4 @@
       .dn_rx_i(dn_rx)
    );
 
-   SB_IO #(
-      .PIN_TYPE(6'b101001),
-      .PULLUP(1'b0)
-   ) u_usb_p (
-      .PACKAGE_PIN(usb_p),
-      .OUTPUT_ENABLE(tx_en),
-      .D_OUT_0(dp_tx),
-      .D_IN_0(dp_rx),
-      .D_OUT_1(1'b0),
-      .D_IN_1(),
-      .CLOCK_ENABLE(1'b0),
-      .LATCH_INPUT_VALUE(1'b0),
-      .INPUT_CLK(1'b0),
-      .OUTPUT_CLK(1'b0));
-
-   SB_IO #(
-      .PIN_TYPE(6'b101001),
-      .PULLUP(1'b0)
-   ) u_usb_n (
-      .PACKAGE_PIN(usb_n),
-      .OUTPUT_ENABLE(tx_en),
-      .D_OUT_0(dn_tx),
-      .D_IN_0(dn_rx),
-      .D_OUT_1(1'b0),
-      .D_IN_1(),
-      .CLOCK_ENABLE(1'b0),
-      .LATCH_INPUT_VALUE(1'b0),
-      .INPUT_CLK(1'b0),
-      .OUTPUT_CLK(1'b0));
-
-   // drive usb_pu to 3.3V or to high impedance
-   SB_IO #(
-      .PIN_TYPE(6'b101001),
-      .PULLUP(1'b0))
-   u_usb_pu (
-      .PACKAGE_PIN(usb_pu),
-      .OUTPUT_ENABLE(dp_pu),
-      .D_OUT_0(1'b1),
-      .D_IN_0(),
-      .D_OUT_1(1'b0),
-      .D_IN_1(),
-      .CLOCK_ENABLE(1'b0),
-      .LATCH_INPUT_VALUE(1'b0),
-      .INPUT_CLK(1'b0),
-      .OUTPUT_CLK(1'b0));
-
 endmodule