MicroNova Mercury 2 with SymbiFlow counter_test attempt

--------- Makefile changes ---------

else ifeq ($(TARGET),mercury2)
  PARTNAME:= xc7a35tftg256-1
  XDC:=${current_dir}/mercury2.xdc
  BOARD_BUILDDIR := ${BUILDDIR}/mercury2

--------- mercury2.xdc  ---------

set_property BITSTREAM.GENERAL.COMPRESS TRUE [current_design}]

# Clock pin
set_property PACKAGE_PIN N14 [get_ports {clk}]
set_property IOSTANDARD LVCMOS33 [get_ports {clk}]

# LEDs
set_property PACKAGE_PIN M1 [get_ports {led[0]}]
set_property PACKAGE_PIN A14 [get_ports {led[1]}]
set_property PACKAGE_PIN A13 [get_ports {led[2]}]
set_property IOSTANDARD LVCMOS33 [get_ports {led[0]}]
set_property IOSTANDARD LVCMOS33 [get_ports {led[1]}]
set_property IOSTANDARD LVCMOS33 [get_ports {led[2]}]

# Clock constraints
create_clock -period 20.0 [get_ports {clk}]

--------- counter.v ---------

module top (
    input  clk,
    output [2:0] led
);

    localparam BITS = 3;
    localparam LOG2DELAY = 22;

    wire bufg;
    BUFG bufgctrl(.I(clk), .O(bufg));

    reg [BITS+LOG2DELAY-1:0] counter = 0;

    always @(posedge bufg) begin
        counter <= counter + 1;
    end

    assign led[2:0] = counter >> LOG2DELAY;
endmodule