User guide

13-14
SDF Backannotation
Using the Shorter Delay in IOPATH Entries
It is valid syntax in an SDF file to have two IOPATH entries for the
same pair of ports but one entry for a rising edge on the input or inout
port and another entry for a falling edge on the input or inout port. For
example:
(IOPATH (posedge inport) outport (3) (6))
(IOPATH (negedge inport) outport (5) (4))
These entries specify backannotating the following delay values to
the module path delay between the port named inport and the port
named outport:
• If a rising edge on inport results in a rising edge on outport, then
the module path delay is three.
• If a rising edge on inport results in a falling edge on outport, then
the module path delay is six.
• If a falling edge on inport results in a rising edge on outport, then
the module path delay is five.
• If a falling edge on inport results in a falling edge on outport, then
the module path delay is four.