calling a stored procedure with sqlsrv vs mssql driver needs "EXEC " prefix

Just posting this here for people scratching their head when moving from mssql driver to sqlsrv driver.

if you are calling a stored procedure e.g.

$this->db->query('get_data @parameter=?', $parameter)

this works under mssql driver
when using sql driver you should change it to

$this->db->query('EXEC get_data @parameter=?', $parameter)

otherwise you get num_rows=-1 and no results