User guide

13-31
SDF Backannotation
To handle I/O ports, use the INTERCONNECT construct instead of
the DEVICE construct.
Using the INTERCONNECT Construct
The INTERCONNECT construct represents the actual or estimated
delay in the wire between devices.
The following SDF specifies the loading for Figure 13-4:
(INSTANCE CELLTYPE)
(DELAY
(ABSOLUTE
(INTERCONNECT U1/B A (2:3:4))))
In the above statements, the interconnect must be reflected at the
input of the next stage (which is actually the load or tester in this case).
Since this is not available for simulation purposes, this interconnect
is added to the output of the previous stage.
But the intent of the SDF entry was to backannotate to all generics
that use B as an output port. In this case, the following SDF entry
yields correct backannotation:
(DEVICE B (1:2:3))
Multiple Backannotations to Same Delay Site
VCS backannotates source to load delays onto the delay site
associated with the load port. Therefore, there are multiple delay
entries, from different source ports to the same load port. In such
cases, you can specify the delay value that you want to backannotate.