ModelSim Error: (vsim-3009) [TSCALE]

You can always try typing

verror 3009

to see if there is more information about the error you are getting. In this case, it produces

$ verror 3009

vsim Message# 3009:

A module without a `timescale directive in effect, and without

explicit timeunit and timeprecision declarations, uses the

simulator resolution limit for both its time unit and time

precision. This may result in incorrect delays and unintentional

behavior in the module. Beware of simulator performance impact,

and consider using the vlog -timescale or vopt -timescale options

as a workaround. This message can be downgraded to a warning with

-warning 3009, suppressed with -suppress 3009, or suppressed

with +nowarnTSCALE.

[DOC: QuestaSim User's Manual - Verilog Simulation Chapter]