Grass Valley Switcher Products - Manual (Page 116)

116 Switcher Products — Protocols Manual
Section 4 — DPM CPL Protocol
The request address field specifies where the requested information is to be
delivered. This field is only used when subscribing to information via
Krystal’s ethernet interface and is unused for HDLC communications.
The request ID is a user-defined subscription request identifier. It is used in
conjunction with the request address to uniquely identify a subscription.
Because the request ID is sent back as part of the subscription issue, it is
commonly used for subscription issue routing within a control point. The
serial number is also sent back to a control point as part of a subscription
issue. A control point can use this field to qualify a subscription issue. For
example, when a control point changes a subscription, it should modify the
serial number from its previous state. If a subscription issue is received that
contains the old serial number, then that issue should be discarded.
The service ID identifies the desired subscription service. Only parameter
service is supported for the switcher/DPM interface. The parameter
service is used to obtain and/or monitor the present value of one or more
parameters.
The flags field modifies the behavior of the Subscribe command. When the
subscribe immediate flag is set, the requested information is returned
immediately. In essence, the information is returned once upon request
without further updates. The replace service flag is used to replace a
current service subscription (identified by request address, request ID, and
service ID) with a new request. For example, one could replace an existing
parameter service subscription with a new group of parameters.
Note Subscribe immediate results in only one issue with the current value(s).
A subscription for changes is not activated.
Parameter Service
The parameter ID field identifies the parameter of interest 1 . This is followed by a pad field which 32-bit aligns the Device field.
The Device field further qualifies the parameter or group of parameters being requested. In some instances, the device field con-
tains a mask which may be used to request the parameter value of each device specified in the mask. For other parameters, a sep-
arate parameter service request is necessary 2 .
Unsubscribe
The unsubscribe command cancels all or part of a subscription. As one
might expect, the same command data necessary to subscribe to a service,
Table 108. Parameter Service Data
Field Size Value
Parameter ID 2 bytes refer to Appendix B
alignment pad 2 bytes any
Device 4 bytes refer to Appendix B
1. Refer to Parameters on page 121 for a complete list of parameters used for this interface.
2. Refer to Parameters on page 121 for the device types associated with each parameter.