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Do constants need to be in anon-clk'd process's sensitivity list if they are i/ps

 
 
neilmac neilmac is offline
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Join Date: Jan 2008
Posts: 5
 
      02-07-2008
If Ive got a proces like this, which is basically combitorial, do constants need to be in the sensitivity list?

I think not.

In my case the constant is defined in another package, not within the architecture.

Ive put a much simplified examle below where:

inq_addr is an input and REGISTERS_BASE_VALID is a constant.

-------------------------------------------------
-- address decode process
---------------------------------------------------

p_addr_decode: process(inq_addr)


begin

access_type_selected <= NODEV;


if ((inq_addr AND REGISTERS_BASE_VALID) then

access_type_selected <= REGISTER_ACCESS;

end if;


end process p_addr_decode;

Any help appreciated..
 
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mcdjnaja mcdjnaja is offline
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      02-07-2008
Hello,

I think a constant must not be in the sensitivity list because it is constant and a process is evaluated when a signal of the sensitivity list is modified, although a constant will never be modifed.
Moreover, at the synthesis time, synthesis tool will detect the constant and remove it.

Mathieu
 
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mcdjnaja mcdjnaja is offline
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      02-07-2008
More, a signal in the sensitivity list of a process can be replaced by a "wait on" instruction in concurrent statement, so you can wait a long time the modification of a constant...
 
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