Re: attribute 'event usage within procedure

Altera_Forum · ‎10-21-2015

Hi,

I'm having a procedure (non-synthesizable code) and I am trying to use the 'event attribute on a signal declared as input to the procedure:

   procedure priority_req(signal   tb_control : in  t_tb_control) is
   begin
         while (tb_control.command /= priority_grant) loop
            wait for tb_control.cycle_time;
            wait until tb_control.command'event;
         end loop;
   end priority_req;

tb_control is a signal (although mode 'in' within procedure) of type t_command

where t_command is a record.

From the compiler I am getting the error:

Error, attribute event is only defined for signals.

I have tried all language syntaxes from '87 to '2008, all see it as an error.

Does anyone have an ideea how I can fix/rewrite it so it gets compiled?

Altera_Forum · ‎10-21-2015

thats because the 'event attribute is not a signal, and hence cannot be waited on.

instead, use:

wait on tb_control.command;

Altera_Forum · ‎10-21-2015

@Tricky

thank you, the compiler is happy with "wait on".

Is "wait on signal" accomplished on assignment of signal or value change?

Altera_Forum · ‎10-21-2015

Wait on waits until an event occurs on the signals in the list, so you can list multiple signals.

Altera_Forum · ‎10-21-2015

If you want to wait until the the assignment of a signal, you can use:

wait on my_signal'transaction;

So in this case it is every time a signal is assigned, even if it is from the same state, eg:


my_signal <= '1';
wait for 10 ns;
my_signal <= '1';

creates 2 'transactions.

Altera_Forum · ‎10-21-2015

I am using HDL Designer flow and the error I initially mentioned occurs in the "Generation step" of the ModelSim TCL flow.

With the proposed 'transaction attribute the tool passes the generation step but triggeres a compile error in ModelSim:

wait on tb_control.command'transaction;

tb_control is a record containing a signal "command"

ModelSim error:
Attribute "transaction" may not be read from formal signal parameter "tb_control".
VHDL Compiler exiting

It seems that various tools interpret these attributes differently:

1. ModelSim accepts 'event, HDL Designer doesn't

2. HDL Designer accepts 'transaction, ModelSim doesn't