Time and time segments

There are two major "kinds" of time in SmartCGMS architecture - a device time and a logical time.

Device time

Device time is a timestamp representing real, wall-clock time. This timestamp is represented in a measure we call a rat time. The time is encoded as the number of days since January 0, 1900 00:00 UTC, see http://en.wikipedia.org/wiki/January_0. Integral part stores the number of days, fractional part stores the time within the day. It could have been any fixed dates, but this one is compatible with FreePascal, Delphi and Microsoft Products such as Excel, Access and COM's variant in general.

For example, 01 Jan 1900 00:00 would be 1.0 and 01 Jan 1900 24:00 (02 Jan 1900 00:00) would be 2.0, and so on.

The SDK contains rattime.h and rattime.cpp files, which offers functions to convert UNIX timestamps to rat time and vice versa.

Current date and time: 09:26:59 8. 12. 2023
Current unix timestamp: 1702024019
Current rat time: 45268.352071759

Logical time

Logical time is an increasing sequence of numbers, assigned to device events as they are created. This helps us mark the logical sequence of device events, and sort them by the time of their creation.

Preferably just one global source of logical time should be present per single SmartCGMS-based simulation. However, since the SmartCGMS is partially ready for distributed applications, more logical time sources (and more logical time sequences) may be present. The synchronization between more logical clocks is currently unsupported.

Time segments

Time segments are a set of measured values, bounded by two markers - time segment start and end (device events). This functionality was introduced mainly due to the fact, that more parallel measurements may occur at one time, and so is their processing. In order to process all values from all running measurements independently, the concept of time segments was introduced.

A time segment is identified by its simulation-unique number, which may be persistent based on the configuration. If more time segments with the same segment identifier exist, the conflict must be resolved outside of SmartCGMS context (e.g. by an external script modifying the database, etc.), as the architecture itself is unable to resolve it.

Every time segment must start with the device event marked with Time_Segment_Start code. This device event contains a device time, that is less or equal to a value of the first level of such segment. Then, a set of levels, parameters and other data relevant to this segment may be sent through the filter chain. When the time segment reaches its end (e.g.; its last level from database was sent), a device event marked with Time_Segment_End code must occur. This marker allows for proper resource deallocation, and also marks the end of the time segment visually in drawings.

Any device event containing the time segment identifier sent outside of device time boundaries (marked with Time_Segment_Start and Time_Segment_End events) is ignored and will be discarded. It is also worth noting, that any relevant device event should also have its logical time within corresponding boundaries (logical times of given markers).

A time segment might also be seen as an entity implementing a certain interface. For more info, see the signal model page.