Grass Valley 2200 - Manual (Page 95)

5-5
General Protocol Notes
General Protocol Notes
The protocol used for this interface is designed around setting values and
receiving status (values). A subscription mechanism provides for status updates
when changes occur providing more timely delivery of information without
constant and frequent polling.
The interface is not designed as a pure master/slave relationship; both the
switcher and DPM have responsibility for part of the communications and
function more as peers: The switcher forwards source selection button presses to
the DPM and orchestrates running effects; the DPM sends video, key, and front/
back information to the switcher to control aux busses.
This protocol is derived from one used for internal communications between the
Grass Valley Krystalª Digital Picture Manipulator control panel and effect
manager via an ethernet connection. Much of the message structure is to support
communications between multiple panels and multiple effect managers but was
retained for consistency. The Krystal panel to effect manager communications is
not described in this document.
The format of messages is described in ÒMessage FormatÓ on page 5-11.
Message speciÞcs are described in ÒParametersÓ on page 5-19 and ÒOther
Command SpeciÞcsÓ on page 5-21.
Data communications speciÞcs are described in ÒTransmission Media and
ProtocolsÓ on page 5-21.
Communications examples are contained in ÒExamplesÓ on page 5-22.
Message Timing
The timing of some messages is critical in order for the switcher and DPM to
perform in lock step. These are considered real time messages.
The run control messages sent by the switcher to the DPM must be acted on in a
Þxed number of video Þelds from when they are sent by the switcher. A delay
adjustment is provided to compensate for variations in devices.
Source changes sent by the DPM to the switcher will be processed so that the
video will change at the beginning of the next Þeld.
All other messages do not have a deterministic requirement and are processed
differently within the switcher.
Transmission of real time messages should be given priority over the
nondeterministic ones. The maximum packet size was choosen to allow for
interleaving high priority messages when several low prioirty messages are
awaiting transmission.