The XML format for connecting Open Curves to a real-time data source is described below. The root element is "connection" and contains either a "serial" or "network" child element.

connection

Children - serial, network

The root document element.

serial

Parent - connection
Children - buffer, time, comms

The serial element specifies the use of a serial data connection. It is mutually exclusive of the network element.

Attribute	Description
port	Identifies the serial comm port to connect on ("COM3", "/dev/ttyUSB0").
baud	Specifies the serial baud rate.

network

Parent - connection
Children - buffer, time, comms

The network element specifies the use of a TCP or UDP connection. It is mutually exclusive of the serial element.

Attribute	Description
address	The connection address.
port	The target connection port.
protocol	Either "tcp" or "udp".

buffer

Optional: Determines the size of the ring buffer Open Curves uses to store data samples.

Attribute	Description
size	The number of data elements to store in the ring buffer. This number of elements is stored for each "column". Zero size results in the default size being used.

time

Optional: The time element can be used to identify the index of the timestamp column in the incoming data, and/or to adjust the timescale. The timestamp column is used to timestamp each incoming data value. The index is specified by the column attribute. The scale attribute is used to scale the read time stamps into seconds. The default is 1.

Attribute	Description
column	Optional, one based index identifying the timestamp column index (default zero, for no column).
scale	Optional time scale multiplier used to convert the time column into seconds. The default is 1.

comms

Parent - serial or network
Children - onconnect, headings, receive, ondisconnect

Identifies how to communicate over the selected protocol. Communication may be binary or text-based as indicated by the binary attribute. The binary selection affects how descendants of this element are formatted.

Attribute	Description
binary	Optional, "true" to use binary communications, "false" for text based communication. The default is "false".

onconnect and ondisconnect

Parent - comms The onconnect element the message to send when a connection is established, while ondisconnect specifies the message to send just prior to disconnecting. These are intended to be used as handshaking messages, to request the start and end of data transmission. The content of these elements depends on the binary attribute of its parent. In binary mode, elements require a struct child element. In text mode, the element text is used for the message (the text between the start and end tag).

In either communication mode both onconenct and ondisconnect elements are optional and may be omitted.

headings and receive

Parent - comms
Children - heading for headings, or struct for receive Optional: The headings and receive elements specify details about the incoming data, but are mutually exclusive. Use headings when the comms mode is text based and receive in binary mode.

The headings element specifies a list of headings to attribute to incoming data as well as identifying the expected number of incoming data items per message. Incoming messages are parsed in the same was as each line in a text input file. The headings element has a number of heading child elements, one per "column" as defined in the supported formats. Each heading element has a single name attribute which is used as the name for that column.

When omitted, the number of text based samples per line is inferred from the first line, and headings are labelled "Column 1", "Column 2", ...

The receive element defines a binary structure to read and has exactly one struct child.

struct

Parent - onconnect, receive, ondisconnect
Children - field The struct element identifies the binary structure of a message. It is used to define both incoming and outgoing messages, though some attributes of field elements change for each use case.

A struct has any number of field elements, each of which identify a data member of the structure, including type, name and value for outgoing messages. The order of the fields controls the order of serialisation.

The struct has the following attributes:

Attribute	Description
endian	"network", "little" or "big". Network Endian is an alias for "big" as this is commonly used for network transmission. The default is "network".

A field element has the following attributes.

Attribute	Description
type	The attribute data type. Also used for structure alignment and padding. See below.
name	The display name for the field.
heading	Optional, used with `receive` only. Only fields with `heading` set to "true" are plotted. All other fields are ignored. The default is "false".

A field may also have a text value (between the start and end tags), which sets the value for that field. The text must be a valid string for the selected type. Fields with values are only used for onconnect and ondisconnect structures or receive structure fields with a padding type (see below).

The following field types are supported:

Type	Description
int8	8-bit, signed integer
int16	16-bit, signed integer
int32	32-bit, signed integer
int64	64-bit, signed integer
uint8	8-bit, unsigned integer
uint16	16-bit, unsigned integer
uint32	32-bit, unsigned integer
uint64	64-bit, unsigned integer
float	Single precision, 32-bit floating point number.
double	Double precision, 64-bit floating point number.

Additionally, the type may be set to one of the following padding types. A padding type must have a value specified in the element text, which controls how much padding to apply (always in bytes).

Padding Type	Description
`pad`	Pads the structure by skipping the specified number of bytes (relative padding).
`padto`	Pads the structure out to the given byte value (absolute padding). No effect if already beyond this byte.
`padbyfield`	Like `pad`, but but the number of padding bytes is read from a preceding field. The element text matches the name of the field, which must appear before this field.
`padtofield`	Like `padto`, but but the padding byte is read from a preceding field. The element text matches the name of the field, which must appear before this field.

The padtofield may be used as a skip value for variable sized messages; e.g., skip to the end of the message by using a "messagesize" member field for the padding byte position.