#ELBREAD: Warning: Module '<module_name>' does not have a `timescale directive, but previous modules do.

Description:

When I run a top-level testbench file and include a file that has interfaces defined, I receive the above warning. Why do I need to have a timescale directive defined?

Solution:

The `timescale compiler directive specifies the default time unit and precision for all design elements that follow this directive and that do not have timeunit and timeprecision constructs specified within the design element. The `timescale directive remains in effect from when it is encountered in the source code until another `timescale compiler directive is read.