User's Manual

Status Updates
When any route, label, or lock is changed on the Videohub Server by any client, the Videohub
Server resends the applicable status block, containing only the items that have changed. For
example, if serial port 6 has been unlocked, the following block will be sent:
SERIAL PORT LOCKS:
↵
5 U
↵
↵
If multiple items are changed, multiple items may be present in
the update:
OUTPUT LABELS:
↵
7 New output 8 label
↵
10 New output 11 label
↵
↵
If a card is plugged into or removed from the Universal Videohub, it will send hardware status
blocks for the video inputs, video outputs, and serial ports on that card.
Requesting Changes
To update a label, lock or route, the client should send a block of the same form the Videohub
Server sends when its status changes. For example, to change the route of output port 8 to
input port 3, the client should send the following block:
VIDEO OUTPUT ROUTING:
↵
7 2
↵
↵
The block must be terminated by a blank line. On receipt of a blank line, the Videohub Server
will either acknowledge the request by responding:
ACK
↵
↵
or indicate that the request was not understood by responding:
NAK
↵
↵
After a positive response, the client should expect to see a status update from the Videohub
Server showing the status change. This is likely to be the same as the command that was sent,
but if the request could not be performed, or other changes were made simultaneously by
other clients, there may be more updates in the block, or more blocks. Simultaneous updates
could cancel each other out, leading to a response that is different to that expected.
In the absence of simultaneous updates, the dialog expected for a simple label change is
as follows:
OUTPUT LABELS:
↵
6 new output label seven
↵
↵
ACK
↵
↵
OUTPUT LABELS:
↵
6 new output label seven
↵
↵
The asynchronous nature of the responses means that a client should never rely on the desired
update actually occurring and must simply watch for status updates from the Videohub Server
and use only these to update its local representation of the server state.
920Developer Information