System timing
Data processor unit System Clock
The unit maintains a realtime clock which tracks the current date and precise time. An internal 40 MHz oscillator, which is characterized and calibrated on each unit manufactured, advances the system clock at a precise rate. Optionally, the unit can use a GPS signal from an attached GPS receiver to regulate the internal oscillator, so that the system clock advances at the same rate as GPS time. This option can be enabled or disabled by the user under System > Preferences > GPS sample clock regulation. In this mode, the system date and time are still independent: the time is not set to GPS time, but the clock advances at the same rate as GPS time.
Setting the Date/Time
The system date and time can be set by the user from the System > Date and time page:
- Set manually: The date and time are specified manually by the user.
- Use local time of PC: The date and time are transferred from the PC.
- Use system's internal GPS: The date and time are transferred from an attached GPS receiver.
Each of these options are "one-shot" actions. After the date and time are set, the system clock advances independently using the internal oscillator, which may optionally be regulated by an attached GPS receiver as described above.
The current state of the oscillator regulation is displayed on the Setup > Hardware page. The unit will display Clock regulation: GPS if a GPS signal is currently being used to regulate the rate of the system clock, or Clock regulation: Internal if the internal oscillator is not being regulated.
Synchronization of Attached MX Modules
In all modes, attached MX devices are always synchronized to and regulated by, the parent unit's system clock. The status of this synchronization is displayed in the Setup > Hardware page. The MX module will display one of the following synchronization states:
- Synchronization: PTPv2: The MX module's clock is synchronized to and regulated by its parent unit using PTPv2. Use of a PTPv2 grandmaster clock (any device that is intended to be used as a PTP master with a data processor unit) needs to be configured so its "priority1" setting is "126" or lower (higher priority). On the MX devices "priority1" is set to 128 and is built into the MX firmware.
- Synchronization: Firewire: The MX module's clock is synchronized to and regulated by another attached MX module (which in turn must be synchronized to the data processor unit using PTPv2) using a Firewire cable.
- Synchronization: Unsynchronized: The MX module's clock is not yet synchronized. This indication will appear for a short time after the data processor unit's power-up, or after an MX module is attached or power cycled. The module status should change to PTPv2 or Firewire after a short delay. The data processor unit always configures attached MX modules for synchronization. An MX module that does not synchronize indicates a problem and tests cannot be run until the problem is corrected.