questions related to asynchronous design?

[verylsi]

Hi all,

Recently I was into an asyncronous design..
I have some question in mind..

What will happen if I write rising_edge(some_signal) to capture the transition?
I know the synthesizer will consider this signal as a clock .. and this design is completely asyncronous.
What effect will that make in implementing such designs?

also
If I assign a signal asynchronously for eg.-

signal temp_storage : std_logic_vector(3 downto 0) ;
begin

temp_storage <= input_signal( 3 downto 0);

end;

will this temp_storage stores a value.. as it is not inside a clocked process , it cannot be a flipflop.
Then what it will be? a latch ?
or i wont store anything at all.

I checked in simulation , it stores the value, but I am not sure in terms of hardware.

Please dnt mind the syntax error , I just wanted to explain my question.

Thanks in advance.

 

[syedshan]

Hi all,

Recently I was into an asyncronous design..
I have some question in mind..

What will happen if I write rising_edge(some_signal) to capture the transition?
I know the synthesizer will consider this signal as a clock .. and this design is completely asyncronous.
What effect will that make in implementing such designs?

also
If I assign a signal asynchronously for eg.-

signal temp_storage : std_logic_vector(3 downto 0) ;
begin

temp_storage <= input_signal( 3 downto 0);

end;

will this temp_storage stores a value.. as it is not inside a clocked process , it cannot be a flipflop.
Then what it will be? a latch ?
or i wont store anything at all.

I checked in simulation , it stores the value, but I am not sure in terms of hardware.

Please dnt mind the syntax error , I just wanted to explain my question.

Thanks in advance.

fthe temp_storage does not store the value in your case, it will follow what input_signal(3:0) will be, as soon as inp*** (3:0) change the temp_*** will change.

What will happen if I write rising_edge(some_signal) to capture the transition?

It will induce a FF. Being synchronous and asunchrouns is a relative term. This things inside the rising_ege(some_signal) is synchronous to some_signal, but can be asynch to for example rising_ege(some_signal_2) and and viceversa

hope this helps