In this way, defective clocks can be detected and removed from the peer population. As no packets are exchanged with a reference clock, however, we replace the transmit, receive and packet procedures with separate code to simulate them. Radio and modem reference clocks by convention have addresses in the form 127.127. Most clocks require a serial port or special bus peripheral. A set of utility routines is included to open serial devices, process sample data, edit input lines to extract embedded timestamps and to perform various debugging functions.
Additional information includes the receive timestamp, exception report, statistics tallies, etc.
In addition, there may be a driver-specific unit structure used for local control of the device. The support routines are passed a pointer to the peer structure, which is used for all peer- specific processing and contains a pointer to the refclockproc structure, which in turn contains a pointer to the unit structure, if used. The ppsclock module is an interface for the PPS signal provided by some radios. The existing assignments are in the Reference Clock Drivers page and its dependencies. The standard clock driver interface includes a set of common support routines some of which do such things as start and stop the device, open the serial port, and establish special functions such as PPS signal support.