Rivendell Netcatcher Communication Protocol

This defines the IP protocol used for communication between different
modules of Rivendell and the 'rdcatchd' daemon.

Connection to ripcd is by means of a TCP SOCK_STREAM connection to TCP
port 6006.  The format of a message is as follows:

     <cmd>[<arg>][...]!

where:

<cmd> is a two-letter code indicating the nature of the message.
<arg> is zero or more arguments.
! is an ASCII character 0x21.


UNPRIVILEDGED COMMANDS -- no authentication is required to execute these.

DC! -- DROP CONNECTION
End the session and drop the TCP connection.

PW <passwd>! -- SEND PASSWORD
Send a password to authenticate the connection.  Ripcd will respond
with 'PW +!' or 'PW -!', indicating the success or failure of the
authentication.


PRIVILEDGED - a connection must be authenticated before these can be
executed.

DE <deck> <number>! -- Deck Event Processed
Sent by RDCatchd whenever a deck event is processed.

RD! -- Reload Deck List
Reload the record/play deck configuration.  Rdcatchd will respond with RD
+!.

RS! -- Reload Event List
Reload the list of scheduled events.  Rdcatchd will respond with
RS +!.

RA <id>! -- Add Event
Add event number <id> to the event list.  Rdcatchd will respond with
RA <id> +!

RR <id>! -- Remove Event
Remove event number <id> from the event list.  Rdcatchd will respond with
RR <id> +!

RU <id>! -- Update Event
Refresh event number <id> in the event list.  Rdcatchd will respond with
RU <id> +!

RE <channel>! -- Request Status
<channel> = Channel number

If <channel> is greater than zero, rdcatchd will respond with 
RE <channel> <status> <id> <cutname>!
<channel> = Channel number

<status> = 0 - Deck is offline
           1 - Deck is Idle
           2 - Deck is Ready
           3 - Deck is active (playing or recording)
           4 - Deck is waiting for GPI

<id> = ID number of current event (from RECORDINGS table)

<cutname> = The cutname of the event (present only for <status>==3).

If <channel> is zero, rdcatchd will respond for every event whose
status is non-idle.

An RE packet will also be sent automatically to all active connections 
upon any change of deck status.


RM <state>! -- Enable/Disable Metering
<state> = 0 - Turn metering off
          1 - Turn metering on

When metering is active, meter data packets will be periodically sent,
as follows:

RM <deck> <chan> <level>!
<deck> = Deck number

<chan> = Channel, 0 = Left, 1 = Right

<level> = Left audio level, in 1/100 of dbFS


SR <deck>! -- Stop
<deck> = Deck Number


PE <id>! -- Purge Event
Received from the daemon upon completion of an event with the ONE_SHOT
flag set, meaning that the event has been removed from the database.


RO! -- Reload Time Offset


RH! -- Reload Heartbeat Configuration


HB! -- Heartbeat Pulse


MN <deck> <state>! -- Monitor State
Turn the input monitor for deck <deck> on or off.


RX! -- Restart dropbox instances


SC <id> <code> <msg>!
Set exit code of event <id> to <code>.