Litem requirements

This document defines the functional requirements for Litems. Read Concentrator requirements and Manager requirements for getting a full vision of the project requirements.

Assumptions

1. A Litem will always be accesible through a network, known as Litem network.

Definitions

1. Litem network: That network shared by a set of Litems.
2. Concentrator request: An operation from the concentrator to the Litem addressed to read/set data fields, invoke actions or subscribe to events
3. A byte corresponds to 8 bits
4. A word corresponds to 16 bits
5. A dword corresponds to 32 bits
6. Any referencie to UTF-8 must be interpreted as 16 bit fixed lenght
7. Event subscription: Action that allows a receiver getting notifications every time that a given event happens in a sender
8. Event unsubscription: Cancellation of a current event subscription
9. Request message: Inquiry that one entity sends another in order to ask for information, task execution or event subscription/unsubscription
10. Response message: Reaction to a request, in which an entity responds with informatio, task execution result or event subscription/unsubscription to a previos request
11. Push message: Reaction to an event triggered in an entity for witch another entity has previously subscribed. The reaction message contains information regarding the triggered event

Requirements

1. Every Litem will have a logical address, independent of the network address it had
2. Litem will allow the concentrator read/set single data fields
3. Litem will allow the concentrator read/set blocks of data fields
4. Litem will allow the concentrator invoke actions
5. Litem will allow the concentrator to subscribe/unsubscribe to Litem events
6. Litem will support byte, word, dword and UTF-8 character datafields
7. Litem will support arrays of the above defined types to be stored in data fields
8. The first byte of on array will contain the number of items stored in the array, therefore the maximum lenght of an array will be 255 items
9. Litem will respond to a concentrator request message with a return code (byte), indicating the request result
10. Depending on the concentrator request nature, the Litem response message will contain, additionally to the return code, data of the types defined in the requirement 6
11. During the time in which an event subscription was active, the Litem will send push messages to the concentrator every time the event was triggered
12. A push message will contain information regarding the event triggered in the Litem