author | Graeme Price <GRAEME.PRICE@NOKIA.COM> |
Fri, 15 Oct 2010 14:32:18 +0100 | |
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<?xml version="1.0" encoding="utf-8"?> |
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<!-- Copyright (c) 2007-2010 Nokia Corporation and/or its subsidiary(-ies) All rights reserved. --> |
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<!-- This component and the accompanying materials are made available under the terms of the License |
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"Eclipse Public License v1.0" which accompanies this distribution, |
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and is available at the URL "http://www.eclipse.org/legal/epl-v10.html". --> |
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<!-- Initial Contributors: |
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Nokia Corporation - initial contribution. |
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Contributors: |
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--> |
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<!DOCTYPE concept |
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PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd"> |
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<concept id="GUID-95BD3650-08CB-407D-969E-DFDB39B2FEFC" xml:lang="en"><title>What is a Platform Service?</title><shortdesc>A platform service is an interface designed to make it |
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quick, easy and inexpensive to integrate hardware into a mobile device.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody> |
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<section id="GUID-F3ACE06A-E619-416A-BC4B-4AA4771404D2"><title>Platform |
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Service</title> <p>A platform service is a set of defined functionality, |
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usually providing an abstraction or encapsulation for functionality |
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provided by hardware.</p><p>For example, a platform service may provide |
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a standard interface for using a serial bus to send commands and data |
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between integrated circuits on the base board. Another example would |
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be providing a standard interface for Direct Memory Access (DMA) hardware |
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for moving blocks of data from one block of memory locations to another |
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or from a block of memory to a hardware device.</p><p>The platform |
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service separates the functionality required by kernel, device driver |
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and application processes from the specific hardware implementation. |
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This means, for example, that a device driver can be written for a |
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platform service that uses the published APIs, without needing to |
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know the specifics of the actual hardware device/chipset.</p><fig id="GUID-D1D306BB-EFDD-4365-8259-39A4F4EB6AE3"> |
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<title>Platform service</title> |
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<image href="GUID-99637158-DE86-4BB4-98D4-3A3E64AB768F_d0e87314_href.png" placement="inline"/> |
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</fig><p>The platform service is a consistent hardware interface at |
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the bottom of the operating system platform software stack. In the |
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past much of the logic and configuration required to enable a new |
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piece of hardware was higher up in the operating system stack and |
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that made it difficult to support new or variant hardware. The platform |
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service architecture separates out the hardware specific interfaces |
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and encapsulates them behind a standard set of platform service (client |
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interface) APIs. </p><p>The platform service consists of :</p><ul> |
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<li><p>Client Interface/Platform service APIs </p></li> |
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<li><p>Implementation of the APIs:</p><ul> |
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<li><p>Platform Independent Layer (PIL)/Framework/Generic implementation</p></li> |
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<li><p>SHAI interface</p></li> |
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<li><p>Platform Specific Layer (PSL)/SHAI Implementation/Hardware |
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implementation</p></li> |
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</ul></li> |
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</ul><p>The PIL contains all the common functionality code such as |
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maintaining a list of available channels for communication or holding |
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the pending list of memory transfers to be processed by DMA when the |
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hardware becomes available. Usually the PIL provides the implementation |
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of the Client Interface APIs. This is sometimes referred to as the |
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Framework.</p><p>The interface between the framework code and the |
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PSL code is known as the Symbian Hardware Adaptation Interface (SHAI). |
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The SHAI interface specifies how the PIL and PSL talk to each other |
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(APIs, shared memory areas etc.)</p><p>The PSL consists of the specific |
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code required to work with a particular piece of hardware. This means |
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that supporting a new or variant chipset only requires the PSL to |
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be amended or to have detection code to handle a particular piece |
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of hardware. </p><p>Some Platform Services, such as GPIO, provide |
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APIs that directly address the hardware, and so the PSL provides the |
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client interface API implementation directly. For example, there is |
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no GPIO PIL/framework.</p></section> |
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<section id="GUID-15BD58D5-12D7-4871-9A98-940F39B95182"><title>Variations |
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on platform service</title><p>Not all platform services are as simple |
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as the diagram above suggests. Some platform services do not talk |
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to hardware directly or at all, but provide a higher-level abstraction, |
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often with further low-level platform services below them in the OS |
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stack. For example, the Power Manager Policy platform service, provides |
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APIs to control power management policy, but does not interface with |
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any hardware directly. In these cases there is either no PSL, or the |
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PSL provides configuration specific responses to a generic PIL. For |
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example, if a handset can be built in two variants, one with a hardware |
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graphics accelerator and one without but with a software emulated |
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graphics accelerator, then the PSL would be responsible for directing |
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graphics requests either to the hardware, or to the software and returning |
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the results back through the PIL to the client.</p><p>Some plaftorm |
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services, for example TV-Out, may use additional platform services |
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to output sound as well as providing hardware support for the TV-Out |
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chipset.</p><p>Some platform services may share a piece of hardware, |
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such as a radio chip. The chip may provide cellular telephony, WiFi, |
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FM radio transmission and other features all on one chip, but there |
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may be several separate platform services, each exposing an API for |
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one particular technology.</p><p>Both the PIL and PSL may make calls |
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to other OS components, including other platform services, for information |
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such as Hardware Configuration, power status, and the availability |
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of other services.</p></section> |
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<section id="GUID-1D50AC84-89A3-4BA3-BB7F-032FF499E56D"><title>Why |
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have a platform service</title><p>Platform services |
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benefit both device creators and third party hardware/chipset developers |
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since they specify a standard software interface between the operating |
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system and standard functionality provided by hardware.</p><p>This |
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means that it is possible for a device creator to easily integrate |
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the best hardware for their device, and allows hardware creators to |
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work to a standard interface that can be used across multiple devices |
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and multiple customers.</p><p>As the platform service interface provides |
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a consistent interface to functionality, it allows the device creator |
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to concentrate on the core functionality and not worry about how the |
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hardware will provide it. And since the interface is standard for |
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each type of hardware component, each manufacturer can provide the |
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information or code for the PSL comparatively easily for each additional |
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variant they produce. So this means less code required from hardware |
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manufacturers per hardware component, and a larger market as each |
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new mobile device, from any device creator, can use that compliant |
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hardware.</p><p>The platform services abstraction for hardware adaptation |
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also means more common code that can be shared across the Symbian |
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Foundation member community. This includes sharing PSL code with other |
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hardware providers, and sharing code for device drivers and other |
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higher-level components that need to use the platform services APIs. |
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For example, if a device driver for a particular piece of hardware |
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also needs to use a serial inter-IC bus (IIC) to send commands to |
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that hardware, then it can use the IIC platform service APIs and re-use |
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code that other components have already tested for using the IIC client |
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interface APIs.</p><p>Platform services also allow the use of standardized |
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test tools and test suites. Each new piece of hardware in a particular |
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category (for example, camera, Bluetooth radio) has to comply with |
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the SHAI interface (PIL/PSL interface). This means that an existing |
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test suite that works with another camera module can be used to test |
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that this new piece of hardware works. This reduces the time taken |
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for testing and increases speed to market.</p></section> |
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<section id="GUID-173DF644-98BC-415C-8DA5-5428FF560622"><title>Who |
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uses the Platform Service?</title><ul> |
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<li><p>Application developers, who need to use the functionality of |
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a hardware device, but do not need to know the specific details of |
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the hardware/hardware implementation. They use the client interface |
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and need to know what the APIs are, and what order they must be called |
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in and so on.</p></li> |
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<li><p>Framework developers, who need to know how to implement each |
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of the client interface APIs , and a description of the functionality |
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required within the framework.</p></li> |
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<li><p>Hardware Developers, who need to understand the hardware interface, |
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and have to write or update the hardware implementation (PSL) to support |
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their particular chipset/hardware.</p></li> |
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</ul></section> |
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<section id="GUID-84DAC762-23F9-4756-8D3A-EB03280E93CA"><title>Platform |
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service client interface APIs</title><p>In general these are function |
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calls, and associated enumerations. There are two main types of function |
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call:<ul> |
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<li><p>Synchronous</p></li> |
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<li><p>Asynchronous</p></li> |
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</ul></p><p>A synchronous function call from the client/device-driver |
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waits for the platform service to process it and make any return value. |
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The client thread waits for the synchronous call to complete.</p><p>An asynchronous function call asks the platform service to do something, |
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but then execution of the client continues immediately. For example, |
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this would be the case of any function that starts a long data transmission |
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or receive process, such as streaming video. One of the standard components |
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of an asynchronous function call is a way for the result to be communicated |
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back to the client. Often this is done by a “callback function” where |
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the client specifies a pointer to a function (and parameters) during |
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the original call, and the platform service puts the callback on the |
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Delayed Function Call (DFC) queue for the client when the platform |
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service has completed the request. This may indicate “transfer completed” |
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or “transfer failed, error code 123”, it may release a lock or other |
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functionality defined by the author of the client.</p></section> |
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</conbody><related-links> |
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<link href="http://developer.symbian.org/wiki/index.php/Prop/SHAI.dita"> |
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<linktext>Symbian Foundation SHAI page</linktext></link> |
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</related-links></concept> |