I'm not familiar with FPGA.
I want to build a frequency counter, and below is my RTL code:
module Edge_counter(
input fin,
input clk,
input rst_n,
output reg [15:0] cnt_out
);
assign gate_n = ~gate;
////sub module////
edge_detector edge_detector(
.clk(clk),
.rst_n(rst_n),
.pulse(fin),
.pos_edge(pos_edge),
);
gate gate1(
.clock(clk),
.rst_n(rst_n),
.gate(gate)
);
memory_store memory_store1(
.clock(gate_n),
.rst_n(rst_n),
.signal_in(cnt_out)
);
////code////
always @(posedge clk or negedge rst_n)begin
if(!rst_n)
cnt_out <= 0;
else if(gate == 1'b1 && pos_edge == 1'b1) //gate 1, pos_edge 1
cnt_out <= cnt_out + 1'b1;
else if(gate == 1'b1 && pos_edge == 1'b0) //gate 1, pos_edge 0
cnt_out <= cnt_out;
else if(gate == 1'b0)
cnt_out <= 0;
end
endmodule
The gate time is 1ms. (0.5ms gate = 1, and 0.5ms gate = 0)
And I use Function Generator to output a FM square wave, the carrier frequency is 60kHz, modulation frequency is 50Hz, and the frequency deviation is 10kHz.
The experiment result looks like this:
I don't think the output value = 29 or 31 is correct, but I have no idea why have these values.
Will the problem comes from Timing analysis? Because I don't know how to correctly constrain all the signal in my design.
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