Initialize all values of timeinfo in make_time_info. This prevents
the field 'tm_isdst' from getting inadvertently set to 1 causing
time to be off by 1 hour.
The use of mktime was causing a fault when called in interrupt handler because on GCC it lock the mutex protecting the environment, To overcome this issue, this patch add dedicated routine to convert a time_t into a tm and vice versa.
In the process mktime has been optimized and is now an order of magnitude faster than the routines present in the C library.
Russ Butler
Vincent Coubard