Warning (14130): Reduced register with stuck data_in port to GND

Hi,

I am getting the warning of Reduced register with stuck data_in port to GND for both "rx_start" and rx_stop" registers. How to work around this. what is the issue ?

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always@ (posedge clk)

begin

if(~reset )

begin

rx_start <= 1'b0;

rx_stop <= 1'b0;

end

else

begin

rx_start <= (scl_in && pre_scl && ~sda_in && pre_sda);

rx_stop <= (scl_in && pre_scl && sda_in && ~pre_sda);

end

end

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