[Gems-users] Variable Latency DRAM memory system

["David T. Wang" <davewang@xxxxxxxxxxx>]

Hi,

    	I just subscribed to the user list, but I am trying to follow up on 
Nazanin's post.

	Basically, what Nazanin is asking for is if GEMS has the facility 
to support a callback function to allow the memory system to return a 
latency value at a later time, after the memory system simulation code 
has had time to wait around a bit, not at request time. We don't want to 
"call a function to find out what the latency is". To do that implies 
that the function has to return right away with the latency of the 
access. What we really want is the ability to issue a memory request into 
a buffer/queue, and then simulate the request through the memory 
subsystem hierarchy. If that request hits a bank conflict, a later 
request may be able to complete earlier, and re-ordering can occur in the 
memory system, but that re-ordering may have effects on the 
deferred/re-ordered request that occured semantically at an earlier time. 
We'd like to be able to simulate all those interactions, re-ordering 
policies and mechanisms.

	What we need is to support a mechanism where a callback function 
can be used to tell the processor(s) that a memory reference has 
completed, not just an external function call to return latency value.

	We're still stumbling around the GEMS code, looking at the slicc, 
but can't quite make heads or tails of it right now. Your help is 
appreciated.  Thank you.

							David