Raises a custom compile-time error. void __error(string format, ...); The __error() function called from a process or a function that is being executed during compile-time or converted to VHDL will stop the compilation and produce a user-defined error. You can use .Net composite format strings to make your error messages more specific.

template <int _Size> entity Inner
{
	port in logic clk;
	
	process dummy ()
	{
		if (pow2(log2(_Size)) != _Size)
			__error("_Size = {1} is not a multiple of 2", _Size);
	}
}

entity Test
{
	Inner<3> uut(
		clk = auto
	);
}

The compilation will fail with an error message: _Size = 3 is not a multiple of 2