error 10559 VHDL

[Altera_Forum]

Hi,  

 I was wondering if anyone can shed some light on this error that I managed to obtain.  Error (10559): VHDL Subprogram Call error at user_functions.vhd(100): actual for formal parameter "s" must be a "signal" This is the chunk of code where the error occurs it is a function designed to count the rising edges on a signal. and this is to be implemented in main body of the code 4 times, as I need a counter for four signals.  FUNCTION COUNTER(Z:std_logic; Reset:std_logic) RETURN natural IS   variable count: natural range 0 to 65535;  variable Q: natural range 0 to 65535;   begin (line 100) if (rising_edge(Z)) then  if Reset = '0' then  count := 0;  else  count := count + 1;  end if;  end if;    Return count;    end; END user_functions;    Is it that I cannot use a subprogram within a new function description?  Let me know if you require more information.

[Altera_Forum]

The rising edge function requires the input to be a signal because it uses various attributes that only exist on a signal. The problem is that Z is a constant.  

 But I don't really understand this function. The variables will be re initialised every time the function is called, so it will only ever return 0 or 1. Why are you using a function and not a process?

[Altera_Forum]

--- Quote Start ---  Hi,   I was wondering if anyone can shed some light on this error that I managed to obtain.  Error (10559): VHDL Subprogram Call error at user_functions.vhd(100): actual for formal parameter "s" must be a "signal" This is the chunk of code where the error occurs it is a function designed to count the rising edges on a signal. and this is to be implemented in main body of the code 4 times, as I need a counter for four signals.  FUNCTION COUNTER(Z:std_logic; Reset:std_logic) RETURN natural IS   variable count: natural range 0 to 65535;  variable Q: natural range 0 to 65535;   begin (line 100) if (rising_edge(Z)) then  if Reset = '0' then  count := 0;  else  count := count + 1;  end if;  end if;    Return count;    end; END user_functions;    Is it that I cannot use a subprogram within a new function description?  Let me know if you require more information.  --- Quote End ---   --------------------------------------------------------------------   Hi ,   I dont where "s" is defined as a signal for variable :  actual for formal parameter "s" must be a "signal"  Also this should be put in a process , functions are mostly used for mathematical or data conversion tasks .  Would help if i could see how is it called within the main architecture .  Regards ,  Ahmed Asim Ghouri Embedded Strings inc Website : www.emstrings.com Email : support@emstrings.com

[Altera_Forum]

You are trying to describe registers (a counter) in a subprogram. That's not possible. Functions must be memoryless and can't respectively use edge sensitive expressions.

[Altera_Forum]

To elaborate a bit about the problem, the only case where a register in a subprogram can be synthesized is a construct like below. But it won't work for a counter because the out port can't be read inside the procedure. 

 procedure ff ( signal clk: in std_logic; signal d : in std_logic; signal q : out std_logic) is begin if rising_edge(clk) then q <= d; end if; end;