The following rules distinguish tasks from functions:

A function shall execute in one simulation time unit;

a task can contain time-controlling statements.

A function cannot enable a task;

a task can enable other tasks or functions.

A function shall have at least one input type argument and shall not have an output or inout type argument;

a task can have zero or more arguments of any type.

A function shall return a single value; a task shall not return a value.