21.8.62 set_max_delay
(Ask a Question)Description
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 the delay_value. The
timing engine 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
multi-cycle path constraint.
You must specify at least one of the -from , -to, or -through arguments for this constraint to be valid.
set_max_delay delay_value [-from from_list ] [-to to_list ] [-through through_list ]Arguments
| Parameter | Type | Description |
|---|---|---|
delay_value | floating point | Specifies a floating point number in nanoseconds that represents the required maximum delay value for specified paths.
|
from | list of strings | 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 | list of strings | 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. |
through | list of strings | Specifies a list of pins, ports, nets, or instances (cells) through which the timing paths must pass. |
| Return Type | Description |
|---|---|
integer | Returns the ID of the clock maximum delay constraint. |
Error Codes
| Error Code | Description |
|---|---|
| Error: SDC0021 | Invalid max delay constraint: the -from value is incorrect. |
| Error: SDC0022 | Invalid max delay constraint: the -from is empty. |
| Error: SDC0023 | Invalid max delay constraint: the -to value is incorrect. |
| Error: SDC0024 | Invalid max delay constraint: the -to is empty. |
| Error: SDC0026 | Invalid max delay constraint: the -through is empty |
| Error: SDC0061 | Invalid max delay constraint: Missing or Illegal parameter/value. |
| Warning | cell (get_cells) is incorrect type;"-through" objects must be of type net (get_nets), or pin (get_pins).Note: Constraint will be disabled. |
| Warning | port (get_ports) is incorrect type;"-through" objects must be of type net (get_nets), or pin (get_pins). Note: Constraint will be disabled. |
Supported Families
| PolarFire® |
| PolarFire SoC |
| SmartFusion® 2 |
| IGLOO® 2 |
| RTG4™ |
Example
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*]