set_clock_latency - 2023.2 English

Vivado Design Suite Tcl Command Reference Guide (UG835)

Document ID

UG835

Release Date

2023-10-18

Version

2023.2 English

Capture actual or predicted clock latency

Syntax

set_clock_latency [‑clock <args>] [‑rise] [‑fall] [‑min] [‑max] [‑source]
    [‑late] [‑early] [‑quiet] [‑verbose] <latency> <objects>

Usage

Name	Description
`[-clock]`	List of relative clocks
`[-rise]`	Specify clock rise latency
`[-fall]`	Specify clock fall latency
`[-min]`	Specify clock rise and fall min condition latency
`[-max]`	Specify clock rise and fall max condition latency
`[-source]`	Specify clock rise and fall source latency
`[-late]`	Specify clock rise and fall late source latency
`[-early]`	Specify clock rise and fall early source latency
`[-quiet]`	Ignore command errors
`[-verbose]`	Suspend message limits during command execution
`<latency>`	Latency value
`<objects>`	List of clocks, ports or pins

Description

This command defines a clock's source or network latency for specified clocks, ports, or pins.

Note: This command operates silently and does not return direct feedback of its operation.

Source latency is the time in nanoseconds that a clock signal takes to propagate from its waveform origin to the clock definition point in the design. For example, this would be the time delay for the clock to propagate from its source (oscillator) on the system board to the FPGA input port.

Network latency is the time a clock signal takes to propagate from its definition point in the design to a register clock pin on the timing path. The total clock latency at a register clock pin is the sum of a clock's source latency and network latency.

Arguments

-clock <args> - (Optional) Specifies a list of clocks associated with the <latency> assigned to the specified <objects>. If the -clock argument is not used, the clock <latency> will be applied to all clocks passing through the specified pins and ports.

-rise - (Optional) Defines the latency for the rising clock edge.

-fall - (Optional) Defines the latency for the falling clock edge.

-min - (Optional) Defines the minimum latency for the specified clocks for multi-corner analysis.

-max - (Optional) Defines the maximum latency for the specified clocks for multi-corner analysis.

Note: The -min and -max options are mutually exclusive.

-source - (Optional) Defines the specified <latency> as a source latency. Clock source latencies can only be specified for clock objects and clock source pins.

Note: Without the -source argument the <latency> is considered as network latency.

-late - (Optional) The time delay specified by <latency> is how late the clock edge arrives.

-early - (Optional) The time delay specified by <latency> is how early the clock edge arrives.

Note: The -early and -late options are mutually exclusive, and can only be specified when -source is also specified.

-quiet - (Optional) Execute the command quietly, returning no messages from the command. The command also returns TCL_OK regardless of any errors encountered during execution.

Note: Any errors encountered on the command-line, while launching the command, will be returned. Only errors occurring inside the command will be trapped.

-verbose - (Optional) Temporarily override any message limits and return all messages from this command.

Note: Message limits can be defined with the set_msg_config command.

<latency> - (Required) The amount of clock latency, specified as nanoseconds, to apply.

<objects> - (Required) The clock, port, or pin objects on which to apply the latency. Specifying pin or port objects assigns the latency to all register clock pins in the transitive fanout of the pins or ports. If -clock is used, the latency is applied to all register clock pins of the specified clocks.

Note: If <objects> specifies a clock, the -clock argument is unnecessary, and is ignored.

Examples

This example will set an early latency on the rising edge of CLK_A.

set_clock_latency -source -rise -early 0.4 [get_ports CLK_A]