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Address: 127.127.28.u
Reference ID: SHM
Driver ID: SHM
This driver receives its reference clock info from a shared memory-segment. The shared memory-segment is created with owner-only access for unit 0 and 1, and world access for unit 2 and 3
struct shmTime {
int mode; /* 0 - if valid set
* use values,
* clear valid
* 1 - if valid set
* if count before and after read of
* values is equal,
* use values
* clear valid
*/
int count;
time_t clockTimeStampSec; /* external clock */
int clockTimeStampUSec; /* external clock */
time_t receiveTimeStampSec; /* internal clock, when external value was received */
int receiveTimeStampUSec; /* internal clock, when external value was received */
int leap;
int precision;
int nsamples;
int valid;
int dummy[10];
};
When the poll-method of the driver is called, the valid-flag of the shared memory-segment is checked:
If set, the values in the record (clockTimeStampSec, clockTimeStampUSec, receiveTimeStampSec, receiveTimeStampUSec, leap, precision) are passed to ntp, and the valid-flag is cleared.
If not set, a timeout is reported to ntp, nothing else happend
When the poll-method of the driver is called, the valid-flag of the shared memory-segment is checked:
If set, the count-field of the record is remembered, and the values in the record (clockTimeStampSec, clockTimeStampUSec, receiveTimeStampSec, receiveTimeStampUSec, leap, precision) are read. Then, the remembered count is compared to the count now in the record. If both are equal, the values read from the record are passed to ntp. If they differ, another process has modified the record while it was read out (was not able to produce this case), and failure is reported to ntp. The valid flag is cleared.
If not set, a timeout is reported to ntp, nothing else happend