Specifications

Software Interface 43
3.3.3 Commands and Messages
This section describes the formats of commands and messages. The
host uses the command ring in shared memory to send commands to
the module. The module uses the message ring in shared memory to
send messages to the host. A message is a reply to a previous command.
Typically, a command can cause DECvoice to return many messages. The
module processes the commands in the order they enter the ring. Also,
the module sends messages to the host in the order that the messages
occur.
All command and message entries in the rings are prefixed with a
message tag. The message tag is a 32-bit longword at the top of each
command and message entry. The software driving DECvoice uses the
message tag to track messages and commands. Many commands cause
DECvoice to return a corresponding message to the host. The message
tag informs the driving software which message belongs with which
command. DECvoice does not interpret the message tag. The message
tag is only significant to the driving software.
3.3.3.1 Command Format
A command consists of a fixed-size command header, followed by a block
of command-specific data. Figure 3-5 shows the command format.
MA-0559-88
Figure 3–5 Command Format
MSGTAG
The message tag informs the driving software which messages belong
with which commands. DECvoice does not interpret the message tag. The
message tag is only significant to the driving software.