<?xml version="1.0" encoding="utf-8"?>

<!-- Copyright (c) 2007-2010 Nokia Corporation and/or its subsidiary(-ies) All rights reserved. -->

<!-- This component and the accompanying materials are made available under the terms of the License 

"Eclipse Public License v1.0" which accompanies this distribution, 

and is available at the URL "http://www.eclipse.org/legal/epl-v10.html". -->

<!-- Initial Contributors:

    Nokia Corporation - initial contribution.

Contributors: 

-->

<!DOCTYPE concept

  PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">

<concept id="GUID-4E5B1276-07D1-562A-8EE8-21DDE78D2CE5" xml:lang="en"><title>System

State Management Policy</title><prolog><metadata><keywords/></metadata></prolog><conbody>

<p>The System State Management (SSM) policy determines the set of permissible

states, state transitions, and the tasks that are performed while changing

the system state. This policy is associated with a transition in system state

or a system-wide property. </p>

<p>This policy is defined by a system state policy plug-in and an associated <codeph>CommandList</codeph> resource

file. The policy in SSM is contained in policy DLLs and resource files. The

policy DLLs are identified using the requested system state or system-wide

property (example <codeph>SysStatePolicy&lt;stateIdentifier&gt;</codeph> and <codeph>SysPropertyPolicy&lt;propertyIdentifier&gt;</codeph>). </p>

<p>In addition to defining an interface for this framework, some command tasks,

such as reading <codeph>commandList</codeph> s of a resource file format into

memory, is also provided. This is implemented as a 'C' class which provides

implementation of this common functionality. But, it still contains some pure

virtual functions, similar to the <xref href="GUID-067293BF-B28C-3CEC-92F4-1351A795EA7F.dita"><apiname>CActive</apiname></xref> class for active

objects. </p>

<p>When implementing a new policy DLL, choose to start from scratch and extend

from the framework’s 'M' Class, or to use the 'C' class which provides the

basic functionality and is expected to be commonly used in policy DLLs. The

policy DLL is dynamically loaded and an object is instantiated that implements

one of the following interfaces (M Class): </p>

<p>The policy DLLs are customizable by licensees. The framework for the policy

DLLs are described by the APIs detailed in the following table. </p>

<table id="GUID-3E8474F9-9D83-5995-B98E-29CDC3B74516">

<tgroup cols="3"><colspec colname="col0"/><colspec colname="col1"/><colspec colname="col2"/>

<thead>

<row>

<entry><p><b>Interfaces (M Class) :</b> </p></entry>

<entry><p><b>API</b></p></entry>

<entry><p><b>Description</b></p></entry>

</row>

</thead>

<tbody>

<row>

<entry><p>For system state </p> </entry>

<entry><p> <xref href="GUID-A86FEEA6-7602-34A9-A200-E2521CB66BD4.dita"><apiname>MSsmStatePolicy</apiname></xref>  </p> </entry>

<entry><p>This is an Session Initiation Protocol (SPI) which allows customization

of the behavior of state changes. </p> </entry>

</row>

<row>

<entry><p>For system-wide property </p> </entry>

<entry><p> <xref href="GUID-31FB0BC8-83FC-3581-A7A3-C1781CAE7187.dita"><apiname>MSsmSwpPolicy</apiname></xref>  </p> </entry>

<entry><p>This is an SPI which allows customization of the behavior of the

system-wide property changes. </p> </entry>

</row>

</tbody>

</tgroup>

</table>

<section><title>Transition of a system state</title> <p>The system state (and

its sub-states) is distributed through the Domain Manager (DM). A specific

command in a <codeph>commandList</codeph> is used to set a new value for the

system state (that is SysCLE interfaces with the DM to change the system state).

The new value of a system state is distributed through the DM and the appropriate

Domain Hierarchy. For more information on SysCLE, see <xref href="GUID-1F2911DC-7D71-573D-AFD2-1EA4BBA88A57.dita#GUID-1F2911DC-7D71-573D-AFD2-1EA4BBA88A57/GUID-E2D75D7D-98A5-5419-8B0E-0A995D3EFEC9">System Command List Executer</xref>. </p> <p>When a change of a system state

is requested: </p> <ol id="GUID-7B67F54E-91A7-52FF-91E6-93E66B7B3654">

<li id="GUID-3DCB2900-E1DE-5A01-9C42-794E49CD0903"><p>SysStateMgr calls <codeph>TransitionAllowed(..)</codeph> to

ascertain if the requested system state transition is allowed. </p> </li>

<li id="GUID-C76D73C1-24D5-575E-A014-13629DAF2B3B"><p>If the requested transition

is allowed, the SSM policy loads the policy plug-in, <codeph>GetNextCommandList(..)</codeph>. </p> </li>

<li id="GUID-533853A3-4950-5067-B5F8-46B30E1A7AEA"><p> <codeph>GetNextCommandList(..)</codeph> obtains

the initial <codeph>commandList</codeph> for this system state. </p> </li>

<li id="GUID-B9D92285-0D0F-5B99-8B40-F1C66CE53593"><p>The new system sub-state

is returned by the policy plug-in. The returned commandList object is passed

to SysCLE. </p> </li>

<li id="GUID-31463C2B-0531-52C7-A524-56A75A5C3280"><p>SysCLE runs the <codeph>commandList</codeph>,

and provides a return code to indicate if the <codeph>commandList</codeph> is

run successfully. </p> </li>

<li id="GUID-9BBA2C2D-02C8-5059-88C8-3A7AA08C7ABD"><p>This return code and

the system sub-state is used in a call to <codeph>GetNextCommandList(..)</codeph>.

This returns the next <codeph>commandList</codeph> or NULL (indicating that

there are no more <codeph>commandLists</codeph> for this system state). </p> </li>

</ol> <p>Command lists stored in resource files can be implemented in one

of the two ways: </p> <ul>

<li id="GUID-FBE223B7-EA0E-579B-B3B4-EECA95B31FD0"><p>Single resource file

containing multiple commandLists - </p> <p>This option leads to only a single

file being opened at a system state transition. </p> <p>For example, on instantiation

of the system state policy object, the associated resource file is opened,

and this contains an array of commandLists which are used in specific system

sub-states). This reduces any impact on device start-up time because of opening

multiple resource files. </p> <p> <b>Note:</b> A single resource file containing

multiple commandLists for a particular system state is currently the preferred

solution. </p> </li>

<li id="GUID-FCD34DF4-8B38-5039-A026-10DEAAFAE16B"><p>Many resource files,

each containing a single <codeph>commandList</codeph> - </p> <p>Multiple resource

files make distinction between different commandLists very clear. This increases

maintainability and eases debugging of commandLists. </p> </li>

</ul> <p><b>Example of system state transition from ‘Normal’ to ‘Shutdown’</b> </p> <p>The

following image illustrates an example of the policy actions performed when

the system state is transitioned from ‘Normal’ to ‘Shutdown’. </p> <fig id="GUID-C6D2D6B9-FE2D-5265-94EC-DF1D6128ACA9">

<title>                 System state transition from 'Normal' to 'Shutdown'

              </title>

<image href="GUID-1686AFA7-F0FA-5B3D-9E2F-EE2D7CDC338B_d0e165699_href.png" placement="inline"/>

</fig> <p><b>Symbian defined system state transitions</b> </p> <p>The following

events cause transitions in Symbian defined system state: </p> <ol id="GUID-D8F4E705-1C48-5222-956E-0D74835EEDD6">

<li id="GUID-9BFC161B-D1CE-5BB4-868A-F86E432E12BC"><p> <b>Undefined -&gt; Start-up:</b>  </p> <p>In

this transition, <filepath>SysStateMgr</filepath> is created by <codeph>EStart()</codeph>,

the start-up system state is assumed. The start-up policy plug-in is used

to select the correct ‘activities list’ for start-up. For example by reading

the start-up Mode. </p> </li>

<li id="GUID-5F43C1F2-57F1-5341-914C-DA389037627A"><p> <b>Start-up -&gt; Normal

:</b>  </p> <p>In this transition, when the start-up state is finished, the

last item in the commandList indicates to <filepath>SysStateMgr</filepath> that

the Normal state should be entered. </p> </li>

<li id="GUID-A5E578ED-06D0-5FD5-B268-9CA7EF4E4DB1"><p> <b>Normal -&gt; Shutdown:</b>  </p> <p>This

transition is generated by the Look and Feel (LaF) Shutdown manager or another

component in the device responsible for handling device shutdown, after detection

of a shutdown event. </p> </li>

<li id="GUID-B526B171-5654-50AA-9482-D20D4D549D28"><p> <b>Start-up/Normal/Shutdown

-&gt; Fail:</b>  </p> <p>This transition can occur at any time, and it involves

immediate interruption of the current commandList and immediate emergency

shutdown of the device. </p> </li>

</ol> <p>When distributing the system state, the domains existing in the Domain

Manager hierarchy to be traversed in different directions, based on which

state is being handled. Components higher up in the system model requires

shutdown notification before components below them. Similarly components lower

down in the system model need to be notified of start-up before components

above them. The two possible options for accomplishing this using the domain

hierarchy is to: </p> <ul>

<li id="GUID-C2FDB7E4-CFC0-5C5D-A473-791268AE59DC"><p> <b>Have a separate

domain hierarchy for each system state</b> - </p> <p>This option would have

four separate domain hierarchies, one for each of the system states. The current

system state is defined by the domain hierarchy which is currently in a defined

state, or by a separate system state indication. </p> </li>

<li id="GUID-ABC31988-39BD-5F11-AD8B-87F26B89001D"><p> <b> Traverse the same

domain hierarchy in different directions, depending on the system state</b> - </p> <p>This

option has one domain hierarchy with the current system state that is defined

by the state of the domain hierarchy. This is the preferred option because

of the simplicity in changing state and registering for notification of state

transitions. </p> </li>

</ul> </section>