User guide

13-2
SDF Backannotation
Using SDF Files
The OVI Standard Delay File (SDF) specification provides a standard
ASCII file format for representing and applying delay information.
VCS supports the OVI versions 1.0, 1.1, 2.0, 2.1, and 3.0 of this
specification.
In the SDF format a tool can specify intrinsic delays, interconnect
delays, port delays, timing checks, timing constraints, and pulse
control (PATHPULSE).
When VCS reads an SDF file it “backannotates” delay values to the
design, that is, it adds delay values or changes the delay values
specified in the source files. You tell VCS to backannotate delay
values with the $sdf_annotate system task.
There are twomethods that you can use to backannotate delay values
from an SDF file:
• Compiling the SDF file at compile time.
This method is preferable in almost all cases and VCS does this
by default.
• Reading the ASCII SDF file at run time
This method remains chiefly for compatibility purposes.