wait for signal in process

[Xin Xiao]

I have two modules: one is a cache memory and the other is a RAM memory.

I have this piece of code inside a process with sensitivity list (in
cache.vhd):

Mem_address <= ...;
Mem_RW <= '0'; -- We want to read
Mem_enable <= '1';
Result := Mem_result;

....

Mem_result is a signal connected to the RAM module data output. I think this
is wrong because I can't expect the RAM to put the values in the output
instantly. Right? How could I "wait" for the RAM to put the output and then
storing it in variable "Result"?

What I thought is to put the line "Result := Mem_result;" inside another
state (cache.vhd is a FSM). I think this would work but I'm open to other
suggestions as well.

thanks

 

[KJ]

I have two modules: one is a cache memory and the other is a RAM memory.

I have this piece of code inside a process with sensitivity list (in
cache.vhd):

Mem_address <= ...;
Mem_RW <= '0'; -- We want to read
Mem_enable <= '1';
Result := Mem_result;

...

Mem_result is a signal connected to the RAM module data output. I think
this is wrong because I can't expect the RAM to put the values in the
output instantly. Right?

Depends on exactly what you're trying to model. In any case, 'instantly' in
simulation is still at least one simulation delta so 'Result' won't change
at the exact same time as whatever signal transition causes the process to
wake up if that's your concern.

How could I "wait" for the RAM to put the output and then storing it in
variable "Result"?

Result <= Mem_result after 5 ns; -- For a 5 ns delay

What I thought is to put the line "Result := Mem_result;" inside another
state (cache.vhd is a FSM). I think this would work but I'm open to other
suggestions as well.

Keep it simple.

KJ