vector event

[Matt North]

Does anyone know of a neat way of knowing when an event has occurred in a
vector I.e. changed value.
Their are attributes for this in signals i.e. S'EVENT, S'TRANSACTION etc,
but these cant be used on arrays. (that's what Leonardo tells me!)

I basically want to reset a counter when a vector changes its value.
I am now looking at writing a procedure which periodically compares a
registered form of the vector with its current state.
Messy!!

Thanks,
Matt

 

[VhdlCohen]

Does anyone know of a neat way of knowing when an event has occurred in a
vector I.e. changed value.
Their are attributes for this in signals i.e. S'EVENT, S'TRANSACTION etc,
but these cant be used on arrays. (that's what Leonardo tells me!)

I basically want to reset a counter when a vector changes its value.
I am now looking at writing a procedure which periodically compares a
registered form of the vector with its current state.
Messy!!

S'event SHOULD work on a vector when any bit of a vector canges value.
if S'event then ...

S'transaction should also work on a vector, and the s'transaction is a signal
of type "bit" that would toggle when an assignment is made.
wait on S'transaction.

S'active is like the 'event, except it works on an assignment, even if same
value is reassigned.
if s'active.
So far, this is good for testbench design.

For synthesis, this is another issue.
s'event is for a clock, and I don't believe that it would work for synthesis.
For your counter example, you can do this in a cloked process:
if (In_vector_reg /= In_vector) then
counter <= (others => '0');
----------------------------------------------------------------------------
Ben Cohen Publisher, Trainer, Consultant (310) 721-4830
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Author of following textbooks:
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0-9705394-2-8
* Component Design by Example ", 2001 isbn 0-9705394-0-1
* VHDL Coding Styles and Methodologies, 2nd Edition, 1999 isbn 0-7923-8474-1
* VHDL Answers to Frequently Asked Questions, 2nd Edition, isbn 0-7923-8115
------------------------------------------------------------------------------

 

[Mike Treseler]

Matt North wrote:

I basically want to reset a counter when a vector changes its value.
I am now looking at writing a procedure which periodically compares a
registered form of the vector with its current state.

Something like this?

library ieee;
use ieee.std_logic_1164.all;

entity watch is
port (clk :in std_ulogic;
reset :in std_ulogic;
watch_this :in std_logic_vector(7 downto 0);
change_strobe ut std_ulogic
);
end entity watch;

architecture synth of watch is --Thu Nov 6 09:56:14 2003 treseler
begin
this: process (clk, reset) is
variable last_watch : std_logic_vector(watch_this'range);
constant init : std_logic_vector := (watch_this'range => '0');
begin -- process
if reset = '1' then
change_strobe <= '0';
last_watch := init;
elsif rising_edge(clk) then
if watch_this /= last_watch then
change_strobe <= '1';
last_watch := watch_this;
else
change_strobe <= '0';
end if;
end if;
end process this;

end architecture synth;

-- Mike Treseler

 

[Matt North]

Thanks for your help.

Matt