AR# 47815

Vivado Constraints - How do I convert an ISE FROM:TO: value constraint to XDC?

Description

How do I convert the following ISE FROM:TO constraint to XDC?

NET "clk_rx" TNM_NET = "TNM_clk_rx";
NET "clk_tx" TNM_NET = "TNM_clk_tx";
TIMESPEC TS_clk_rx_to_clk_tx = FROM "TNM_clk_rx" TO "TNM_clk_tx" 5 ns;
TIMESPEC TS_clk_tx_to_clk_rx = FROM "TNM_clk_tx" TO "TNM_clk_rx" 5 ns;

Solution

If this FROM:TO is to be a multi-cycle (for example, 2x the period) constraint, then use the following:

set_multicycle_path -from [all_fanout -from [get_nets clk_rx] -flat -endpoints_only] -to [all_fanout -from [get_nets clk_tx] -flat -endpoints_only] -setup 2
set_multicycle_path -from [all_fanout -from [get_nets clk_rx] -flat -endpoints_only] -to [all_fanout -from [get_nets clk_tx] -flat -endpoints_only] -hold 1
set_multicycle_path -from [all_fanout -from [get_nets clk_tx] -flat -endpoints_only] -to [all_fanout -from [get_nets clk_rx] -flat -endpoints_only] -setup 2
set_multicycle_path -from [all_fanout -from [get_nets clk_rx] -flat -endpoints_only] -to [all_fanout -from [get_nets clk_tx] -flat -endpoints_only] -hold 1

If clk_rx and clk_tx are clocks and have period constraints (for example, create_clock constraints with -name clk_rx/clk_tx), the set_multicycle_path constraints can also be:

set_multicycle_path -from [get_clocks clk_rx] -to [get_clocks clk_tx] -setup 2
set_multicycle_path -from [get_clocks clk_rx] -to [get_clocks clk_tx] -hold 1
set_multicycle_path -from [get_clocks clk_tx] -to [get_clocks clk_rx] -setup 2
set_multicycle_path -from [get_clocks clk_tx] -to [get_clocks clk_rx] -hold 1

If this FROM:TO is to be an explicit requirement, then use the following:

set_max_delay -from [all_fanout -from [get_nets clk_rx] -flat -endpoints_only] -to [all_fanout -from [get_nets clk_tx] -flat -endpoints_only] 5
set_max_delay -from [all_fanout -from [get_nets clk_tx] -flat -endpoints_only] -to [all_fanout -from [get_nets clk_rx] -flat -endpoints_only] 5

If clk_rx and clk_tx are clocks and have period constraints (for example, create_clock constraints with -name clk_rx/clk_tx), the set_max_delay constraints can also be:

set_max_delay -from [get_clocks clk_rx] -to [get_clocks clk_tx] 5
set_max_delay -from [get_clocks clk_tx] -to [get_clocks clk_rx] 5

Note: the example in this Answer Record is not applicable for all designs.

Users are responsible for validating their design constraints.

For more information on the ISE FROM-TO Constraint, please refer to UG625 and UG612.

For more information on Vivado set_multicycle_path and set_max_delay constraints, please refer to UG903.

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AR# 47815
Date	10/15/2014
Status	Active
Type	General Article
Tools	Vivado Design Suite

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