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SPECIFICATIONS.md

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Specifications

Resource description

The remote sensors that the programmer wants to access are specified in the resource.json file. It can contain the following fields:

  • gateway: specifies how to access the gateway sensor

    • url: the machine on which the gateway sensor is connected
    • connection: the connection between the machine and the gateway sensor (for now only usb is supported)

  • nodes: specifies the types of measurement

    • measurement type: temperature, humidity, light, ... as specified in [gatewayMote/popwin_messages.h]
    • direction: "IN" for sensor or "OUT" for actuators

    { "gateways":[ { "url": "localhost", "connection": "usb" } ], "wsns":{ "nodes":[ { "measurementType": "temperature", "direction": "IN" }, { "measurementType": "humidity", "direction": "IN" }, { "measurementType": "light", "direction": "IN" } ] } }

Examples of resource files can be found resources.json and multi_gw.json.

Messaging

In the low-level part of the system (that uses the publish/subscribe messaging model) the following types of models are implemented: notification, publication and subscription. Please note that unsubscriptions are not implemented yet but their structure is identical to subscription messages.

Messages structures

Messages can be contained into fixed-size C structures that contain the full data

  • struct SubscribeMessage
  • struct NotifyMessage
  • struct PublishMessage

The messages can contain the following fields:

  • MeasurementType: An enum that specifies the type of measurement: temperature, vibration, humidity, ...
  • MeasurementUnit: An enum that specifies the measurement unit: Celsius, seconds, meters, ...
  • PublicationType: An enum that specifies the type of publication: e.g. led
  • ID : The id of the sender
  • DataType : An enum that specifies the type of the data: double, int or string
  • data : A buffer of character (of size BUFFERDATASIZE=64) that contains the data. For compatibility between systems integers and floats are printed to this buffer and not stored as bit value.
  • DataSize : The size of the above data in characters

Notification message

struct NotifyMessage
{
	enum MeasurementType measurementType;
	enum DataType        dataType;
	unsigned short       id;
	enum MeasurementUnit unit;
	size_t               dataSize;
	char                 data[BUFFERDATASIZE];
};

Publication message

struct PublishMessage
{
	enum PublicationType publicationType;
	enum DataType        dataType;
	unsigned short       id;               // not mandatory, for convenience
	size_t               dataSize;
	char                 data[BUFFERDATASIZE];
};

Subscription message

struct SubscribeMessage
{
	unsigned short       id;               // Id is not mandatory. Only for convenience
	enum MeasurementType measurementType;
	enum DataType        dataType;
};

Print the messages to buffer

The message structures can be written to and read from a buffer of char. This is used when the message needs to be bufferized.

This can be done with the following functions (example for notification messages):

/// Print message to buffer
///
/// @param x_msg        Incoming message structure
/// @param xp_buffer    Output buffer
/// @param x_bufferSize Size of the buffer for safety
int bufferizeNotifyMessage(const struct NotifyMessage* x_msg, char* xp_buffer, size_t x_bufferSize);

// Read message from buffer
/// 
/// @param xp_msg        Output: message structure
/// @param x_buffer      Input:  message is read from here
/// @param x_maxDataSize Size of the data buffer for safety
int unbufferizeNotifyMessage(struct NotifyMessage* x_msg, const char* x_buffer, size_t x_dataSize);

The full specification of interface can be read from gatewayMote/popwin_messages.h