TcMenu - TagVal protocol documentation

embedCONTROL local area transmissions use a protocol called TagVal. TagVal is a simple and lightweight protocol that has implementations on device for Arduino and mbed, Java as an API and there is also a .NET implementation. As its name suggests TagVal is a Tag to Value protocol, somewhat like a Map in most high level languages.

If you are working in a language where an API is provided, you don’t need to understand the protocol as the API deals with the protocol.

Before reading this, I recommend that you’ve tried generating a menu, read through at least the quick start documentation and the reference material (see getting the code section on the right).

The basics of a TagVal message

In tcMenu a message always starts with the byte 0x01 followed by the protocol; which in the case of TagVal is 0x01. Following the protocol ID is the protocol specific block, here we discuss TagVal protocol. Finally all messages end with a <0x02> regardless of protocol.

Let us take a look at the simplest possible message in wire format:

<0x01><0x01>HBHI=3000|<0x02>

Now lets breakdown that message into parts:

Byte	Data	Meaning
0	<0x01>	Start of msg
1	<0x01>	Protocol (tag val is 1)
2	HB	Message type field
4	HI=3000	Heartbeat interval field
11	|	Field separator
12	<0x02>	End of msg

We can see from the above table that messages start with 0x01 and are followed immediately by the protocol, following this for TagVal messages the two character field will be followed by an equals sign and the value. Field keys must be exactly two characters and the values must be shorter than the definition MAX_VALUE_LEN on the Arduino side (default 40). Every field must be terminated with a pipe symbol, after the last pipe symbol there must be a <0x02> which marks the end of message.

Types supported within messages

String fields are free-form and can contain the pipe character by escaping it the same way as C a string.

Version fields in TagVal are packed into an integer, where major version is multiplied by 100 and the minor version added to it. For example 1.2 would be (100 * 1) + 2 or 102. The most minor version is not presented, as it’s assumed that breaking changes would never occur in a patch release.

MenuIDs are integer values that represent a menu item uniquely.

Boolean values are 0 for false and 1 for true.

The platforms and types are defined within RemoteTypes.h within the embedded library and also in the APIs.

Messages and their contents

In TagVal protocol, every message has a message type which is the first two characters of the message, and there must be a processor on both sides that can convert this message into something appropriate. Message types, like fields are restricted to two bytes in length. It again makes them very easy to process on the embedded side. There is a list of message types and fields in RemoteTypes.h.

Below, we go through the format of each message type.

All connections start by sending a heartbeat with mode set to START to the remote. The remote wil respond to this by sending back a join message. Next, we send either a join or pairing request to either start a connection or in the case of pairing, to store our ID with the device.

In the case of pairing, the device sends back an Acknowledgement, indicating if the pairing succeeded. This is the end of the connection and a hearbeat of type END should be sent and the connection closed.

In the case of a regular connection, the device also sends an acknowledgement, and if unsuccessful that is the end of the connection, a heartbeat of type END should be sent and the connection closed. Otherwise, we proceed to bootstrapping, where the menu structure on the device is communicated to the client. This starts with a bootstrap start, followed by the boot items then a bootstrap end. Once the bootstrap end is received the connection is ready.

Pairing message (type: PR)

Authentication can be enabled on to the embedded side, and when it’s enabled before the first connection the application will need to pair it’s UUID with the server. UUID’s are a 36 character string that universally uniquely identifies that client. In most cases the UI or other connecting component would generate a UUID on installation or first run and keep that ID for subsequent connections. Any connection that is used for pairing should be closed after receiving an acknowledgement from the server.

Example:

PRNM=Lighting|UU=575d327e-fe76-4e68-b0b8-45eea154a126|

Field definitions:

Field	Type	Description
NM	String	The name of your UI
UU	String	UUID of your UI

Join Message (type: NJ)

Join message is used when a new connection is made, to indicate the details about that connection. It MUST be sent on a connection before any other message. It contains the name and UUID key for a given client which will be checked with the authenticator. If you receive an acknowledgement indicating an error immediately after joining, then the join attempt failed.

Example:

NJNM=Lighting|UU=575d327e-fe76-4e68-b0b8-45eea154a126|VE=100|PF=0|

Field definitions:

Field	Type	Description
NM	String	Name for connection
IC	UUID	UUID Key for UI
NE	Version	The version of the sender
PF	Platform	The platform of the sender
UU	UUID	The UUID of the remote app

Heartbeat Message (Type HB)

Used when there are no messages going to or from the host to keep the connection open. Without these being sent and received at regular intervals, the connection will close at both sides. The server (embedded) side determines the interval by sending it in the first heartbeat. The server must pick up and then use this as the heartbeat interval. The timestamp if set, is for purely informational purposes.

Example:

HBHI=3000|HM=1948119|

HbType:

• 0 - NORMAL a normal heartbeat
• 1 - START indicates the start of a connection
• 2 - END indicates we should close the connection now

Field definitions:

Field	Type	Description
HI	Integer	Duration between heartbeats
HM	Integer	Timestamp when sent
HR	HbType	One of the above enum values

Bootstrap Message (type: BS)

Used to indicate the start and end of a bootstrap. This is normally used to send the contents of the menu tree to the remote side. Usually when items are being sent to the remote, a boot start will occur before, and a boot end after.

Example:

BSBT=START|

Field definitions:

Field	Type	Description
BT	String	Either START or END

AnalogItem boot Message (type: BA)

Represents an AnalogMenuItem that belongs to the menu tree being remotely controlled. Analog items are generally smaller integer values (up to 65355 unique values) that can be controlled by a rotary encoder. The value can be divided to make a fixed point value and an offset can be provided. Any unit name is shown after the value.

Example:

BAPI=0|ID=1|RO=0|NM=Hall|AU=%|AM=100|AO=0|AD=1|VC=0|

Field definitions:

Field	Type	Description
PI	MenuID	The parent ID (or 0 for ROOT)
ID	MenuID	The menu ID
RO	Boolean	Readonly field. True: readonly
NM	String	Name of the menu item
VI	Boolean	True if item is visibile
VC	Integer	The current value
AU	String	The unit name, EG: dB
AM	Integer	The maximum value
AO	Integer	The offset for the value
AD	Integer	The divisor for the value

EnumItem boot Message (type: BE)

Represents an EnumMenuItem that belongs to the menu tree being remotely controlled. These items generally represent a series of choices similar to a combo box.

Examples:

BEPI=0|ID=4|RO=0|NM=On Alm|VC=0|NC=2|CA=All On|CB=Silient|

Field definitions:

Field	Type	Description
PI	MenuID	The parent ID (or 0 for ROOT)
ID	MenuID	The menu ID
RO	Boolean	Readonly field. True: readonly
NM	String	Name of the menu item
VI	Boolean	True if item is visibile
VC	Integer	The current value
NC	Integer	Number of choices to follow

Each choice starts at field CA onwards so choice 2 would be CB:

Field	Type	Description
Cn	String	String value for a choice

BooleanItem boot Message (type: BB)

Represents a BooleanMenuItem that belongs to the menu tree being remotely controlled. These items generally represent yes/no choices. The naming can be set to:

• 0 - TRUE / FALSE
• 1 - YES / NO
• 2 - ON / OFF

Field	Type	Description
PI	MenuID	The parent ID (or 0 for ROOT)
ID	MenuID	The menu ID
RO	Boolean	Readonly field. True: readonly
NM	String	Name of the menu item
VI	Boolean	True if item is visibile
VC	Boolean	The current value
BN	Integer	The naming used see above

TextItem boot Message (type: BT)

Represents any type of menu item that extends from EditableMultiPartMenuItem that belongs to the menu tree being remotely controlled. These items generally represent some text that can be changed in accordance with the type of value the item can hold.

enum EditType { PLAIN_TEXT = 0, IP_ADDRESS = 1 }

Field	Type	Description
PI	MenuID	The parent ID (or 0 for ROOT)
ID	MenuID	The menu ID
RO	Boolean	Readonly field. True: readonly
EM	EditType	The type of data supported
NM	String	Name of the menu item
VI	Boolean	True if item is visibile
VC	String	The current value
ML	Integer	The maximum length

FloatMenuItem boot Message (type: BF)

Represents a FloatMenuItem that belongs to the menu tree being remotely controlled. These items hold a floating point representation up to a given number of decimal places.

Field	Type	Description
PI	MenuID	The parent ID (or 0 for ROOT)
ID	MenuID	The menu ID
RO	Boolean	Readonly field. True: readonly
NM	String	Name of the menu item
VI	Boolean	True if item is visibile
VC	Float	The current value
FD	Integer	Decimal places of precision

RuntimeListMenuItem boot Message (type: BL)

Represents a RuntimeListMenuItem that belongs to the menu tree being remotely controlled. These menu items hold more a list of items. List items are sent as a series of values similar to an enum item, where the value items start with C followed by A onwards for the second char. Where CA would be the first value and CB would be next. Likewise the names for each value use keys starting with cA.

Example:

BLPI=0|ID=4|RO=1|NM=list item|NC=2|cA=N0|cB=N1|CA=0|CB=1|

Field	Type	Description
MT	MsgType	Must be BL
PI	MenuID	The parent ID (or 0 for ROOT)
ID	MenuID	The menu ID
RO	Boolean	Readonly field. True: readonly
NM	String	Name of the menu item
VI	Boolean	True if item is visibile
NC	Integer	Number of list items
cn	String	Name of item N
Cn	String	Value of item N

ActionMenuItem boot Message (type: BC)

Represents an ActionMenuItem that belongs to the menu tree being remotely controlled. These items can only be triggered, and don’t really have a state. When triggered then immediately run the associated callback.

Field	Type	Description
PI	MenuID	The parent ID (or 0 for ROOT)
ID	MenuID	The menu ID
RO	Boolean	Readonly field. True: readonly
NM	String	Name of the menu item
VI	Boolean	True if item is visibile

SubMenuItem (type: BS)

Represents a nested menu in the remote menu.

Field	Type	Description
PI	MenuID	The parent ID (or 0 for ROOT)
ID	MenuID	The menu ID
RO	Boolean	Readonly field. True: readonly
NM	String	Name of the menu item
VI	Boolean	True if item is visibile

Large Integer Boot Message (type: BN)

Field	Type	Description
PI	MenuID	The parent ID (or 0 for ROOT)
ID	MenuID	The menu ID
RO	Boolean	Readonly field. True: readonly
NM	String	Name of the menu item
VI	Boolean	True if item is visibile
ML	String	Maximum length of the number
FD	String	The number of decimal places
VC	Decimal	The latest value

Scroll choice Boot Message (type: BZ)

Field	Type	Description
PI	MenuID	The parent ID (or 0 for ROOT)
ID	MenuID	The menu ID
RO	Boolean	Readonly field. True: readonly
NM	String	Name of the menu item
VI	Boolean	True if item is visibile
NC	String	Number of choices
WI	Integer	For array mode, the item width
EM	Mode	0:Ram, 1:EEPROM 2:Custom
VC	String	Text for choice - see note

Note the text for the current choice also contains the current index, it is in the form index-text so for example index 10 with value “Pizza” would be 10-Pizza. Unlike enum all the values are not known, and there may be many, and they could change.

RGBA8 or RGB8 color Boot Message (type: BK)

Field	Type	Description
PI	MenuID	The parent ID (or 0 for ROOT)
ID	MenuID	The menu ID
RO	Boolean	Readonly field. True: readonly
NM	String	Name of the menu item
VI	Boolean	True if item is visibile
RA	Boolean	True if alpha is included
VC	RGBColor	Html color string - see note

We send the value as a color string in HTML hex format, depending on if alpha is present, it will be either 7 or 9 characters long. EG: #FF55AA or #FF55AADD.

Dialog message (type: DM)

Represents a dialog update in either direction. A dialog is a simple informational message or question that needs to be dismissed in order to proceed. The remote can send an action message in response to a dialog in order to simulate the equivalent of pressing a button. The only type of dialog message that is valid from the remote to the embedded device is ACTION (IE simulating a button press).

enum DialogMode { SHOW = 'S', HIDE = 'H', ACTION = 'A'}

enum ButtonType: byte { BTNTYPE_NONE = 0, BTNTYPE_OK, BTNTYPE_ACCEPT, BTNTYPE_CANCEL, BTNTYPE_CLOSE }

Field	Type	Description
MO	DlgMode	One of the dialog mode values
B1	BtnType	One of the button types
B2	BtnType	One of the button types
HF	String	Free form text of the header
BU	String	Free form text of the buffer

Change value Message (type: VC)

Represents a remote change to a menu item. Depending on the type of menu item that sent the change request the value itself will differ. When you send this type of message, the ordering of fields is important, as the remote cannot store the value. Stick to the order of fields shown in the list below. Correlation ID should be 8 characters long in the form of a 32 bit unsigned hex value. It will be returned to you in the ACK message.

There are three types of change: absolute, relative and list.

• Absolute changes are supported for all types, the present value is overwritten with the new one.
• Relative changes are only supported for Analog and Enum items. The change value is added to the existing value.
• List items are sent as a series of values similar to an enum item, where the value items start with C followed by A onwards for the second char. Where CA would be the first value and CB would be next. Likewise, the names for each value use keys starting with cA.

Example for all except lists:

VCPI=0|ID=4|TC=1|VC=0|

Example for lists.

VCPI=0|ID=4|TC=1|CA=0|CB=1|cA=K0|cB=K1|

Field definitions:

Field	Type	Description
MT	MsgType	Must be VC
ID	MenuID	The menu ID
IC	Correlation	Will be returned in the ACK
TC	Integer	Relative: 0, Absolute: 1, List: 2
VC	Depends	The change value - see above
Cn	Optional	The values for a list
cn	Optional	The keys for a list

Server Acknowledgement Response Message (type: AK)

This message indicates the success or failure of a change sent to the server. It will contain the correlation ID you sent in the request.

The status codes are generally defined below, 0 indicates success, negative values are soft errors that can still be treated as success; whereas positive values indicate hard errors.

Status	Meaning
-1	Value out of range
0	Successful
1	ID lookup failed

Field definitions:

Field	Type	Value
IC	Correlation	Same as the request
ST	Integer	Status code as above

Message processing on the remote side

On the embedded side of the protocol, (eg Arduino device) the messages are managed by a TagValueRemoteConnector. There is a remote connector for each client connecting remotely. It has methods to encode messages onto the wire, take a look at the encode<MsgToSend> methods on the object. Incoming messages are handled by CombinedMessageProcessor of which there is a default implementation that handles everything needed for TcMenu in MessageProcessors.h.

Regular Bluetooth connections

You can establish a Bluetooth connection using regular bluetooth serial, for the embedCONTROL UI and the C# API there is no need to map the device to a COM port (although it may be easier to do so). However, for the Java API you do need to do this step on at least Windows (there should be no need on a Unix system).

The BLE protocol extensions

Bluetooth Low Energy connections (BLE connections) are supported using the UI or C# API only at the moment. If there is sufficient demand, we will look at adding to the Java API.

The protocol uses two characteristics, one for the incoming flow, and one for the outgoing flow:

Key purpose	Uuid	Data held
Service key	8589F957-1916-4B27-BA6D-B0AF36F317EF	The service name
API->Device Characteristic	7E7CA4D5-CF52-4918-BD60-6E98A810F0EB	bytes len = MAX_VALUE_LEN
Device->API Characteristic	D361F4F9-B13D-4118-A6C4-B54CF12EED3C	bytes len = MAX_VALUE_LEN

You must not put a message on the API -> Device channel until the channel is empty - signified by a 0 in the first byte. The device to API channel is a streaming channel, so it must be configured by the central as NOTIFY. (EG: pub-sub mode).

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