LBS System Clock Synchronisation Overview

Introduction

The GPS signal contains accurate time data. LBS can use this data to synchronise the system clock with GPS. The system clock is synchronised with GPS at regular intervals if the difference between GPS time and the system clock time exceeds a threshold time difference.

Key concepts

System clock

The mobile device clock that keeps system time.

Set clock plug-in DLL

An optional licensee ECom plug-in DLL used by LBS to set the system clock. Symbian provides a default class that sets the system clock by calling User::SetUTCTime().

It is only necessary to implement a set clock plug-in DLL if a licensee requires to set the system clock by some means other than by calling User::SetUTCTime().

Whether LBS uses a plug-in DLL or the Symbian default class is configured through the LBS administration service.

UTC

Co-ordinated Universal Time. A worldwide time standard. UTC is derived from the GPS signal and is the time standard used to set the system clock.

API Summary

There are two separate APIs involved with LBS system clock adjustment:

• The LBS Set Clock Plug-in Interface

  Licensees can derive from the interface to create an implementation class. The class is packaged as an ECom plug-in DLL which is loaded at startup and used to set the system clock.

• Automatic clock synchronisation

The LBS Set Clock Plug-in Interface

LBS defines an interface class that is used to create a set clock plug-in DLL.

The interface CGPSSetClockBase is shown in figure 2.

Figure 1. Figure 2. CGPSSetClockBase is the interface for LBS set clock plug-in classes.

To create a set clock plug-in, licensees create a class that derives from CGPSSetClockBase and package it as an ECom DLL.

See How to implement a LBS set clock plug-in DLL for more information.

Automatic clock synchronisation

LBS can perform automatic synchronisation of the system clock. LBS administration settings configure automatic clock synchronisation. The settings define the frequency of automatic clock synchronisation and by how much the system clock and UTC can differ before the clock is synchronised.

LBS system clock settings

LBS administration describes how to configure LBS system clock synchronisation settings using either the LBS Administration API or a repository initialisation file.