Re: [Gems-users] Simics-Ruby wakeup interface

[divya ramakrishnan <tickly2002192@xxxxxxxxxxx>]

Thanks Dan, That cleared up a lot of things. 

Divya

Dan Gibson <degibson@xxxxxxxx> wrote:

The Simics/Ruby interface operates as follows.

Simics Issues a Request to Ruby
Case 1: Fast-Path Hit: Ruby return a stall time of zero.
Case 2: Fast-Path disabled: Ruby enqueues one or more events, depending
on the protocol, to handle the access. Ruby returns a stall time of two
billion cycles.

As simulation continues, the Simics processor is stalled. For
(approximately) each SIMICS_RUBY_MULTIPLIER cycles /observed by Simics/,
Simics makes one call into Ruby's event queue, nominally RunEventQueue().

Each run of the event queue increments the local time (Ruby_cycles), and
processes events for the current Ruby_cycle. Eventually, the processing
of these events handles the request, and Ruby un-stalls the affected
Simics processor with an explicit API call.

Lastly, Simics re-issues the request to Ruby, a peculiarity of the
interface. This re-issue is captured in SimicsDriver as I recall, and is
not observed by higher levels of Ruby in normal operation.

Regards,
Dan


divya ramakrishnan wrote:
> Hi,
>
> I have a very basic question about the flow of control in the
> interface between Simics and Ruby.
> I understand that for every memory access, Simics wakes up Ruby and
> adds the transaction to the event queue. How exactly is this event
> queue triggered [using triggerevents(time)] after the Simics processor
> is stalled?
>
> Is Ruby triggered for every cycle after that till it returns a latency
> and unstalls the processor? Is this triggering done by Simics by
> waking up Ruby every cycle?
>
> It would be great if I could understand this basic flow because I am
> really confused about the network simulation.
>
> Thank you,
> Divya
> University of Cincinnati
>
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