Is it possible to define a VHDL function with no parameters?
I'm trying to compute the number of bits in a record type, but to do so it is necessary to create an instance of that type. Therefore, since I can't just define const BITS = t_rec.a'length + t_rec.b'length, I would like to define a function function BITS() return natural that instantiates a record rec : t_rec and returns rec.a'length + rec.b'length. However, the compiler fails with unexpected '(') at the function declaration, before it even reaches the definition.
I would just include an unused, dummy parameter, but I suspect that the lint tools would complain.
Defining subtypes for each record field in advance of the record would be too verbose.
Complete example:
package pack is function BITS() return natural; end package pack; package body pack is function BITS() return natural is begin return 0; end function; end package body pack;
Error message:
pack.vhd:1:30: empty interface list not allowed
You should leave out the parentheses when defining a function with no inputs, eg:
function BITS return natural is
variable rec : rec_t;
begin
return rec.a'length + rec.b'length;
end function;
You should not include the parentheses when you call the function, either. eg:
report integer'image( BITS );
not
report integer'image( BITS() );