Blackboard communication protocol

Direction --->> means a transmission from the client to a server. Direction <<--- means messages which are sent from the server to a client. The messages are:

Command	Direction	Description
c	--->>	Create component message
d	<<---	Create reply
s	--->>	Subscribe message
z	--->>	Unsubscribe message
p	--->>	Push data message
u	<<---	Update client message
r	--->>	Request data message
l	--->>	List components message
m	<<---	Component list message
a	<<---	ACK / Error message
x	--->>	Delete component message
k	--->>	Command message

Create component message - C

1	4	4	4	n
CMD	TYPE ID	USER ID	USER NAME LENGTH	USER NAME

CMD - command byte
TYPE ID - the type of the component
USER ID - the id number associated with the user name
USER NAME LENGTH - length of the user name field
USER NAME - the user name of the user

Create response - d

1	4	4	4
CMD	TYPE ID	USER ID	COMPONENT ID

CMD - command byte
TYPE ID - the type of the component
USER ID - the id number associated with the user name
COMPONENT ID - identification number assigned to the component

Subscribe message - s

1	4	4	4
CMD	TYPE ID	USER ID	COMPONENT ID

CMD - command byte
TYPE ID - the type of the component
USER ID - the id number associated with the user name
COMPONENT ID - identification number assigned to the component

Unsubscribe message - z

1	4	4	4
CMD	TYPE ID	USER ID	COMPONENT ID

CMD - command byte
TYPE ID - the type of the component
USER ID - the id number associated with the user name
COMPONENT ID - identification number assigned to the component

Push data - p

1	4	4	n
CMD	COMPONENT ID	DATA LENGTH	DATA

CMD - command byte
COMPONENT ID - the intended receiver of this data inside the blackboard. Set to 0xFFFFFFFF to send to all subscribers, and to 0 to send to any one subscriber.
DATA LENGTH - length of the data field
DATA - data to be pushed to the blackboard

Update client message - u

1	4	4	4	4	n
CMD	TYPE ID	USER ID	COMPONENT ID	DATA LENGTH	DATA

CMD - command byte
TYPE ID - the type of the component
USER ID - the id number associated with the user name
COMPONENT ID - identification number assigned to the component
DATA LENGTH - length of the data field
DATA - data message

Request data message - r

1	4	4	4
CMD	TYPE ID	USER ID	COMPONENT ID

CMD - command byte
TYPE ID - the type of the component
USER ID - the id number associated with the user name
COMPONENT ID - identification number assigned to the component

List components message - l

1	4	4	4
CMD	TYPE ID	USER ID	COMPONENT ID

CMD - command byte
TYPE ID - the type of the component
USER ID - the id number associated with the user name
COMPONENT ID - identification number assigned to the component

Component list message - m

1	4
CMD	NUMBER OF COMPONENTS

CMD - command byte
NUMBER OF COMPONENTS - the number of components in the message

The following sequense is repeated NUMBER OF COMPONENTS times in the message:

4	4	4
TYPE ID	USER ID	COMPONENT ID

CMD - command byte
TYPE ID - the type of the component
USER ID - the id number associated with the user name
COMPONENT ID - identification number assigned to the component

ACK / Error message - a

1	1	1	4	n
CMD	ACK MESSAGE COMMAND	STATUS	MESSAGE LENGTH	MESSAGE

CMD - command byte
ACK MESSAGE COMMAND - command byte of the message being acknowledged
STATUS - status byte (error / ok / fail / etc)
MESSAGE LENGTH - length of the message field
MESSAGE - message (if any) associated with the ack / error

Delete component - x

1	4	4	4
CMD	TYPE ID	USER ID	COMPONENT ID

CMD - command byte
TYPE ID - the type of the component
USER ID - the id number associated with the user name
COMPONENT ID - identification number assigned to the component

Command message - k

1	4	4	4	4	1	1
CMD	TYPE ID	USER ID	COMPONENT ID	SENDER CID	SIGNAL	NUMBER OF PARAMETERS

CMD - command byte. Always k for this message.
TYPE ID - the type of the target component(s).
USER ID - the id number associated with the user name sending the message.
COMPONENT ID - identification number assigned to the target component(s).
SENDER CID - identification number assigned to the sender component.
SIGNAL - the signal or command sent to the component.
```
q
```
quits a component,
```
r
```
restarts,
```
m
```
sets a component to manual read mode and requests a single data read (if possible),
```
s
```
sets the component to streaming mode. Upon reception of a m message to a component that does not support single data read, an AckOrError message with code 2 and message "Single data read unsupported" should be returned.
```
p
```
pauses the streaming, if sent to a paused component restarts it.
```
d
```
deletes data items. The parameter in this case must be a data field name used in the component, such as
```
"XAcc Byte"
```
or
```
"Signal Strength"
```
. For identified fields, the current data values should be removed from the Blackboard.
```
g
```
gets data of a component. The reply to it should be a returnData message, targeted to the component identified by SENDERCID. If any parameters are given, they must be valid data field names, such as in the case of deleting data items.
```
t
```
allows setting the read frequency for a component. The parameter in this case is a string representation of the frequency, such as
```
"1200"
```
(parameter length would be 4 in this example). The command message will be acknowledged with an ack message describing the status of the operation.
```
x
```
signifies a component-specific signal. In this case, the parameters are interpreted by the component, and it will act accordingly. The command message will be acknowledged with an ack message describing the status of the operation.
NUMBER OF PARAMETERS - Number of parameters to the SIGNAL. Depends on the SIGNAL used.

The following sequense is repeated NUMBER OF PARAMETERS times in the message:

1	n
PARAMETER LENGTH	PARAMETER DATA

PARAMETER LENGTH - length of parameter data.
PARAMETER DATA - the data of the parameter.

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