Grass Valley Switcher Products - Manual (Page 111)

Switcher Products — Protocols Manual 111
Activity Check
Note The parameter ID used for on screen information is the same as the one used
to communicate on air information from the switcher to the DPM. This can
easily lead to confusion since the same PID is used for different meanings.
In determining on/off screen, the following information should take into
consideration:
• location relative to the output raster of the DPM (e.g., off screen)
• image size (e.g., reduced to zero size)
• rotation (e.g., exactly on edge)
• transparency
• any other processing or transform which may affect visibility
Additional factors include actual use of the incoming signal.
If the video signal is replaced by a matte fill, its incoming video is not on
screen.
If the key input is not used it is not on screen.
If instead, the video signal is used in a self key, then the video is on screen
even if the video is a matte.
Other factors may exist depending on the functionality of the DPM.
In addition, the DPM may subscribe to the DPM’s on air status. This infor-
mation tells the DPM whether or not the switcher has the DPM video or key
on air. The DPM should not incorporate this information in the on screen
status it sends to the switcher.
Activity Check
The activity check provides a mechanism for the switcher to detect a link
failure (disconnected cable, etc.) or a patching/routing a different DPM to
the switcher.
The switcher periodically tests for link activity by sending out a Subscribe
Immediate command for the DPM’s ethernet address. If no response is
received, the switcher notes the time-out. When a response is received after
a timeout, the switcher assumes that subscription issues or other updates
could have been missed and reestablishes communications as if the
switcher had been reset.
If link activity is present, the switcher looks at the value returned from the
DPM. If it is different than the last response, the switcher assumes a dif-
ferent DPM is now connected and reestablishes communications as if it had
been reset.