  Energy is a primary constraint in processor design, and much of that energy
is consumed in on-chip communication. Communication can be intra-core (e.g.,
from a register file to an ALU) or inter-core (e.g., over the on-chip network).
In this paper, we use the on-chip network (OCN) as a case study for saving
on-chip communication energy. We have identified a new way to reduce the OCN's
link energy consumption by using line coding, a longstanding technique in
information theory. Our line codes, called Low-Energy Line Codes (LELCs),
reduce energy by reducing the frequency of voltage transitions of the links,
and they achieve a range of energy/performance trade-offs.
