set_max_delay SDC
set_max_delay (SDC)
Specifies the maximum delay for the timing paths.
set_max_delay delay_value [-from from_list] [-to to_list]
Arguments
delay_value
Specifies a floating point number in nanoseconds that represents the required maximum delay value for specified paths.
-
If the ending point has an output delay specified, the tool adds that delay to the path delay.
-
If the path ending point is on a sequential device, the tool includes clock skew and library setup time in the computed delay.
-
If the path starting point has an input delay specified, the tool adds that delay value to the path delay.
-
If the path starting point is on a sequential device, the tool includes clock skew in the computed delay.
-from from_list
Specifies a list of timing path starting points. A valid timing starting point is a clock, a primary input, an inout port, or a clock pin of a sequential cell.
-to to_list
Specifies a list of timing path ending points. A valid timing ending point is a clock, a primary output, an inout port, or a data pin of a sequential cell.
Supported Families
Fusion, ProASIC3/E, ProASICPLUS, Axcelerator, ProASIC (for analysis), eX (-through option), SX-A (-through option)
Description
This command specifies the required maximum delay for timing paths in the current design. The path length for any startpoint in from_list to any endpoint in to_list must be less than delay_value.
The tool automatically derives the individual maximum delay targets from clock waveforms and port input or output delays. For more information, refer to the create_clock, set_input_delay, and set_output_delay commands.
The maximum delay constraint is a timing exception. This constraint overrides the default single cycle timing relationship for one or more timing paths. This constraint also overrides a multicycle path constraint.
Examples
The following example sets a maximum delay by constraining all paths from ff1a:CLK or ff1b:CLK to ff2e:D with a delay less than 5 ns:
set_max_delay 5 -from {ff1a:CLK ff1b:CLK} -to {ff2e:D}
The following example sets a maximum delay by constraining all paths to output ports whose names start by “out” with a delay less than 3.8 ns:
set_max_delay 3.8 -to [get_ports out*]