Hardware Reference
In-Depth Information
Due to the distributed nature of this architecture, the split connections can be
customized to reflect the turns allowed by the routing algorithm. For example, in a
5-port router for a 2D mesh employing XY dimensioned-ordered routing, splitting
from the Y
output is not necessary since this turn is prohibited.
Several other deterministic and partially-adaptive routing algorithms can be defined
via turn prohibits (Flich et al. 2007 ; Flich and Duato 2008 ). When this customization
is utilized, significant area savings are expected, due to the removal of both buffering
and logic resources. This modular router construction enables packet flow to be
pipelined in a fine-grained manner, implementing all necessary steps of buffering,
port allocation, and multiplexing in a distributed way inside each merging unit, or
across merging units. Also, the placement of merge units does not need to follow
the floor-plan of the chosen NoC topology. Instead, merge units can be freely placed
in space, provided that they are appropriately connected.
C
input to the X
C
3.8
Take-Away Points
Switching packets of flits from many inputs to one or multiple outputs is a combined
operation that merges link-level flow control with arbitration in order to resolve
contention for the same output and guaranteeing that there are available buffer
slots to host the selected flits. The implementation of flow control and arbitration
requires the addition of per-input and per-output state variables that guide all the
intermediate steps that a packet should complete before being able to move to the
selected output port. The addition of a routing computation module transforms a
switch to a network router that can participate in an arbitrary network topology
allowing incoming packets to find their path towards their destination.
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