Clock Synchronization To An External Time Reference (Etr) - Novell LINUX ENTERPRISE SERVER 11 - ADMINISTRATION Administration Manual

work. For this purpose, they are assigned special IP addresses in the form
127.127.t.u. Here, t stands for the type of the clock and determines which driver
is used and u for the unit, which determines the interface used.
Normally, the individual drivers have special parameters that describe configuration
details. The file /usr/share/doc/packages/ntp-doc/drivers/driverNN
.html (where NN is the number of the driver) provides information about the particular
type of clock. For example, the "type 8" clock (radio clock over serial interface) requires
an additional mode that specifies the clock more precisely. The Conrad DCF77 receiver
module, for example, has mode 5. To use this clock as a preferred reference, specify
the keyword prefer. The complete server line for a Conrad DCF77 receiver
module would be:
server 127.127.8.0 mode 5 prefer
Other clocks follow the same pattern. Following the installation of the ntp-doc
package, the documentation for ntp is available in the directory /usr/share/doc/
packages/ntp-doc. The file /usr/share/doc/packages/ntp-doc/
refclock.html provides links to the driver pages describing the driver parameters.
20.4 Clock Synchronization to an
External Time Reference (ETR)
Support for clock synchronization to an external time reference (ETR) is available. The
external time reference sends an oscillator signal and a synchronization signal every
2**20 (2 to the power of 20) microseconds to keep TOD clocks of all connected servers
in sync.
For availability two ETR units can be connected to a machine. If the clock deviates for
more than the sync-check tolerance all CPUs get a machine check that indicates that
the clock is out of sync. If this happens all DASD I/O to XRC enabled devices is stopped
until the clock is synchronized again.
The ETR support is activated via two sysfs attributes; as root enter:
echo 1 > /sys/devices/system/etr/etr0/online
echo 1 > /sys/devices/system/etr/etr1/online
278 Administration Guide