User guide

13-34
SDF Backannotation
Note:
In delay value lists in delay definition entries in an SDF file, you
can list one, two, three, or six delay values. Lists of twelve values,
that also specify delays for transitions to and from X are not yet
implemented.
The +multisource_int_delays compile-time option tells VCS to
use a special algorithm for multisource INTERCONNECT delays.
This algorithm simulates different delays from each of the multisource
output or inout ports to the load input or inout port, or in other words,
true pin to pin delays.
Omitting the +multisource_int_delays Option
If you omit the +multisource_int_delays option, VCS uses an
older algorithm that creates an MIPD (Module Input Port Delay) to
model the INTERCONNECT delay. Omitting the option, therefore,
has the following drawbacks:
• If you specify multiple sources with multiple INTERCONNECT
entries for connecting more than one output or inout port instances
to a particular input or inout port instance, this algorithm uses the
longest delays in these INTERCONNECT entries for the delays
in the MIPD so the delay propagating from all sources will be the
same.
• MIPDs only take three delay values for transitions to 1, to 0, and
to Z. If your INTERCONNECT entry has six delay values, the
MIPD only uses the first three so the Z to 1 delay is the same as
the 0 to 1 delay, the 1 to Z delay is the same as the 0 t0 Z delay,
and the Z to 0 delay is the same as the 1 to 0 delay.