GRASS VALLEY PERFORMER, Instruction Manual

Page: 173 / 182

3-55
Serial Protocol Descriptions
Notes About SMPTE Message Processing
Message processing uses a buffer that can contain up to 200 bytes
to hold outgoing messages. All messages waiting to be sent are
concatenated together into a single message block NOT
surrounded by a BLOCK command (see below), which is placed
in the message buffer and sent at the next message send time. The
controlling machine must therefore be careful not to request too
much information at one time, lest it overflow the buffer. If this
buffer does overflow before the bus controller polls and responds
to the router service request to send the data, the entire buffer
contents are cleared and replaced with a system service error
(SERR) message indicating buffer overflow.
SERR (08, System Service Error) is also sent when a system service
message is encountered (byte code between 00 and 1F) that
Performer cannot handle, or when a message that it can handle
contains a bad data item.
CERR (29, Common Error) is sent when a common message is
encountered (byte code between 20 and 3F) that Performer cannot
handle, or when a message that it can handle contains a bad data
item.
Any SERR and CERR that is generated as a result of a bad value
in the message or inability to perform the message function
contains all data bytes of the message, from the command
keyword up to the data byte at which the error was detected.
Since the type-specific messages do not have an error response
message, CERR is sent when a type-specific message is received
that has an error in it.
IFRE (32, Information Field Item Response) is sent in response to
a READ message or a previous UPDATE request.
STUR (40, Startup Response) is sent when the router is powered
up or reset.