Using the -add_delay switch

Hello,

I'm setting an output delays on DDR interface for a signal named "valid" relative to a clock named "clock" as follows:

set_output_delay -clock clock -max -0.9 [get_ports {valid}]

set_output_delay -clock clock -min -2.7 [get_ports {valid}]

set_output_delay -clock clock -clock_fall -max -0.9 [get_ports {valid}] -add_delay

set_output_delay -clock clock -clock_fall -min -2.7 [get_ports {valid}] -add_delay

As far as I understand - a port can have only one -max and one -min delay assinged to it. If more then one is used, the first will be overwritten - UNLESS -add_delay is used.

This is why -add_delay was added when setting the relationship for the falling edge of edge of the clock.

Is this correct ?

Or should I use -add_delay also for the first set ? As follows :

set_output_delay -clock clock -max -0.9 [get_ports {valid}] -add_delay

set_output_delay -clock clock -min -2.7 [get_ports {valid}] -add_delay

set_output_delay -clock clock -clock_fall -max -0.9 [get_ports {valid}] -add_delay

set_output_delay -clock clock -clock_fall -min -2.7 [get_ports {valid}] -add_delay