Civil Engineering Reference
In-Depth Information
the FF's can be merged or shared as shown in Figure 10.10(b), resulting in a
total cost of only three FF's.
To model the maximal FF sharing, the work in [LS91] introduces a mirror
vertex for each gate that has more than one fanout, as shown in Fig-
u r e 10.11, t h e details of which can be found in [Sax85]. Each edge in addi-
tion to having a weight now also has a width In Figure 10.11, the
edge weights are shown above the edges while the edge widths are shown below
the edges. Consider a gate with fanouts to gates To model
the maximum sharing of FF's, an extra edge is added from each fanout gate,
to the mirror vertex,
with a weight of
Here,
is the maximum weight on any fanout
edge of gate
Each of the edges from the gate to its fanouts
and from the
fanouts to the mirror vertex has a width of
i.e.,
The original LP in (10.15) is modified to include the effect of register sharing
as follows:
