Grass Valley Performer SD - Manual (Page 174)

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Section 3 — Operation & Service
The SMPTE standard document, on page 37, shows in Figure 11c
that a BLOCK keyword can surround a group of messages, and
that additional messages can both precede and follow the block of
data in the same supervisory-level message block. The SMPTE
Supplement 1 to 3245-E says, on page 15 under the description of
the BLOCK command, that the command shall be used on every
occasion where message concatenation is employed. These two
seem to conflict with each other. At any rate, Performer sends
outgoing messages without a BLOCK command, and parses
incoming messages with or without BLOCK commands.
The SPECIFIC MUTE message definition does not explicitly say
that more than one information field can be supplied, wrapped in
a BEGIN/END construct. However, since this is the usual
definition in other parts of the standard, Performer allows that
construct.
Likewise, the PRESET message definition does not explicitly say
that more than one information field name/value pair can be
supplied, wrapped in a BEGIN/END construct. Again, this
construct is allowed by Performer.
The following I/F names can be used in a PRESET message:
MATRIX, LEVEL, SOURCE, and DESTINATION pointers. In
particular, note that sources-to-destination and destinations-to-
source may NOT be used.
The PRESET message will not allow the MATRIX, LEVEL,
SOURCE, or DESTINATION pointers to be set to values that are
invalid for this matrix. The SMPTE standard does not say whether
invalid I/F values can be set or not.
The SMPTE standard does not say what should be returned for the
LEVEL CONFIGURATION information field if the matrix pointer
or level pointer is set to an invalid value. Since Performer does not
allow invalid values to be set, this is not a problem.
The LEVEL CONFIGURATION information is of limited
usefulness because there is no message for determining the
allowed limits of the matrix pointer and the level pointer. This
router requires the matrix pointer to be 0 and the level pointer to
be between 0 and 2 (wildcard values are allowed too).