Grass Valley Switcher Products - Manual (Page 112)

112 Switcher Products — Protocols Manual
Section 4 — DPM CPL Protocol
The value which the DPM returns is unimportant. However, if multiple
DPMs exist in a facility it is a good idea to report different values from each
one to allow the switcher to detect a change in DPM connections.
The activity check is optional. The interface behaves normally even if the
DPM never responds to the switcher’s query. However, the switcher will
not be able to recover from link failures, patching or routing without a reset
from one of the two devices.
The switcher queries the DPM approximately every 20 seconds.
Running Effects
During initialization, the switcher subscribes for the DPM’s current effect
number. When a switcher effect is learned, the DPM’s current effect
number is stored as part of the effect.
When that effect is recalled at the switcher (DPM 1 level enabled), the
switcher will send out a command to recall the DPM effect. (SET,
PID_CURRENT_EFFECT).
At the time of the recall, the switcher also issues a SET,
PID_EFFECT_POSITION. The time value sent is zero if REVERSE on the
switcher E-MEM effect memory system is turned off; or to the ending time
of the switcher’s effect if REVERSE is on.
As an effect is running, the switcher sends out commands every field to the
DPM to SET the effect position (PID_EFFECT_POSITION). This same
mechanism supports runs via the RUN button as well as the switcher’s run
lever arm. Other time positioning controls on the switcher panel (PREV KF,
NEXT KF, REWIND, etc. also result in the sending of a new effect position
to the DPM. In this way, the DPM exactly follows the timeline of the
switcher’s effect.
Subscription
Status information is gathered indirectly as a result of a “subscription”
request. The request tells the other device where to send changes to the
specified parameter. The changes are delivered to the requestor in an
“issue” message which may contain several parameter “articles”. Many
articles may be contained in one subscription. Consider a magazine sub-
scription: The reader subscribes to the magazine and whenever new infor-
mation is available, a new issue is delivered to the readers home. The
reader does not have to specifically request each new issue of the magazine.
The “subscribe immediate” mechanism is like requesting a trial magazine
issue - you only get one. Subscriptions may be canceled at any time. The
requestor can also modify the terms of delivery at will.