Functions:-This puts time information into a shared memory segment for the ntp daemon to use. static struct shmTime *getShmTime(int unit) This requests a block of shared memory to communicate to the ntp daemon. It returns a pointer to the memory on success or NULL on failure. void ntpshm_init(struct gps_context_t *context, bool enablepps) Attaches all ntp shared memeory segments. int ntpshm_alloc(struct gps_context_t *context) This allocates a free ntp shared memory segment.If one is available, initialise it for use and flag it as in use.Returns the segment number on success or -1 on failure. bool ntpshm_free(struct gps_context_t *context, int segment) This releases a previously allocated ntp shared memory segment. Indicates the outcome by returning true (success) or false. int ntpshm_put(struct gps_device_t *session, double fixtime) If the shared memory index allocated to the session is valid and the shmTime structure of the session is valid, store the time of the fix.Success is indicated by a return value of 1 and errors are indicated by a return value of 0. int ntpshm_pps(struct gps_device_t *session, struct timeval *tv) Only available if the 1PPS function is compiled in.Checks if the shared memory structures are valid. If so, it validates that the time received is within the locking range.If good, the time is stored in the shared memory.A return value of 1 indicates successful update; 0 indicates there is a problem with the shared memory structures and -1 indicates that the time could not be locked to. Notes based on $Id: ntpshm.c 3771 2006-11-02 05:15:20Z esr $