def _total_microsec(t1, t2):
td = t1 - t2<EOL>return (td.seconds + td.days * <NUM_LIT> * <NUM_LIT>) * <NUM_LIT:10> ** <NUM_LIT:6> + td.microseconds<EOL>
Calculate difference between two datetime stamps in microseconds.

:type t1: :class: `datetime.datetime`
:type t2: :class: `datetime.datetime`
:return: int

.. rubric:: Example

>>> print(_total_microsec(UTCDateTime(2013, 1, 1).datetime,
...                       UTCDateTime(2014, 1, 1).datetime))
-31536000000000