The Symbian OS (779886), страница 60
Текст из файла (страница 60)
See Figure 10.6.• The Cryptography Library implements (since Symbian OS v7) nonRSA-based cryptographic support for symmetric and asymmetricciphers, hash functions, random number generation, and passwordencryption.• The Zip Compression Library is a port of the zlib compression library(see relevant RFCs e.g. RFC1950) used to support compression anddecompression of SIS files (the native Symbian OS installable application format) and Java Archive (JAR) files, and for PNG decompression.Low Level Libraries and FrameworksCrypto.LibraryFeatureReg.ZIPCompressionLibraryPluginFrmwk.Pw. &ShutdownMgmt.ApplicationUtilitiesFigure 10.6 Low-level libraries and frameworks274THE BASE SERVICES LAYER• The Plug-in Framework is a framework and server for plug-in interfaceimplementations.
It defines the standard base classes used by conforming plug-ins and a client-side API used by framework clients tolocate and load plug-ins on demand. It manages a registry of availableplug-ins and implements security policy mechanisms (e.g. capabilitypolicing).• The Power, Memory and Disk Management component is a customizable user-side power manager supporting policy-driven powermanagement via power domain ‘profiles’ at device switch-on andswitch-off. It includes a notification service (the so-called ‘ShutdownServer’) to clients to provide ‘save data’ and ‘release resources’ notifications in case of switch-off, low memory and similar events.• The Application Utilities component, known to developers as BAFL,provides an assortment of utilities organized as a single library DLLincluding utility classes for resource-file handling and file finding, andimplementations of string pools and descriptor arrays.• The Feature Registry (introduced in Symbian OS v9.2) provides an APIenabling run-time queries to discover whether known but optionalfeatures are supported on the run-time platform.Character Conversion CollectionThis collection provides a character-code conversion framework andplug-ins.
See Figure 10.7.Table 10.5 Character Conversion ComponentsComponent NameDevelopment NameCharacter Encodingand ConversionFrameworkCHARCONV ONGOINGCharacter Encodingand ConversionPlug-insCHARCONVCharacter ConversionChar.Encode.Conv.Frmwk.Char.Encode.Conv.PluginsFigure 10.7 Character Conversion componentsCOMPONENT COLLECTIONS275• The Character Encoding and Conversion Framework supports conversion of text between Unicode and non-Unicode character sets.Symbian OS native text formats are Unicode.• The Character Encoding and Conversion Plug-ins provide conversionbetween a variety of ASCII and UTF-7 and UTF-8 text formats. TheUnicode text format is UTF-8.Persistent Data Storage CollectionThe persistence model, plus the DBMS abstraction implemented as alayer around it, provides an SQL-interface for database applications.
Italso includes the Central Repository that provides a uniform approach topersistent settings management. See Figure 10.8.Table 10.6 Persistent Data Storage ComponentsComponent NameDevelopment NameStoreSTOREDBMSDBMSCentral RepositoryCENTRALREPOSITORY• The Store component defines the Symbian OS persistence modelbased on the two abstractions of streams and stores, providing anapplication data-storage model which shields applications from theunderlying File Server implementation.• The DBMS component defines a general relational database accessAPI and implementations for fast client-side-only exclusive access andslower client–server-based shared-access databases. Databases canbe manipulated either through a native API or a subset of SQL.• The Central Repository component provides a single persistent storefor global settings as well as a notification mechanism allowing clientsto register interest when settings change.
The Central Repository wasintroduced in Symbian OS v8.Persistent StorageStoreFigure 10.8DBMSCentralRepositoryPersistent Data Storage components276THE BASE SERVICES LAYERXMLXMLFrmwk.XMLParserWBXMLParserFigure 10.9 XML componentsTable 10.7 XML ComponentsComponent NameDevelopment NameXML FrameworkXMLXML ParserXMLPARSERPLUGINWBXML ParserWBXMLPARSERXML CollectionXML support includes an extensible framework and parser plug-ins forparsing and validating XML documents (see Figure 10.9).• The XML Framework provides an extensible framework for XML parsing based on a parser model similar to SAX-2.0 and supporting DTDand processing plug-ins (for example, validators and auto correctors)as well as parser plug-ins.• The XML Parser component is a non-validating parser plug-in for XML1.0.• The WBXML Parser component is a parser plug-in for WAP BinaryXML (WBXML).Media Device Framework CollectionThe Media Device Framework (see Figure 10.10) defines standard hardware acceleration APIs which are used by the Multimedia Frameworkand its clients, enabling multimedia controller plug-ins to communicatewith hardware accelerator adaptors through standard interfaces.• The Media Device Framework contains standard acceleration APIs foraudio, video, MIDI, and Automatic Speech Recognition (ASR).• Media Device Framework Plug-ins is an ASR Client Utility API thatprovides speaker-independent speech recognition to the MultimediaCOMPONENT COLLECTIONS277Framework and directly to other clients wanting to interface to speechrecognition hardware (or software emulations).Media Device FrameworkMediaDeviceFrmwk.MediaDeviceFrmwk.PluginsFigure 10.10 Media Device FrameworkTable 10.8 Media Device Framework ComponentsComponent NameDevelopment NameMedia DeviceFrameworkMDFMedia DeviceFramework Plug-insAUDIODEVICE,MDFAUDIOHWDEVICEADAPTER,VORBISDECODERPROCESSINGUNIT,VORBISENCODERPROCESSINGUNIT,MDFVIDEODECODEHWDEVICEADAPTER,MDFVIDEOENCODEHWDEVICEADAPTER11The Kernel Services and HardwareInterface Layer11.1 IntroductionThe Kernel Services and Hardware Interface layer (see Figure 11.1) isthe lowest layer of Symbian OS.
It contains the Symbian OS kernel andsupporting components.These include the kernel-level components which must be customizedin order to bring up a minimal build of the operating system on new hardware (although a typical port entails customizing other components too).UIFrameworkApplicationServicesOSServicesBaseServicesKernelServices &HardwareInterfaceFigure 11.1Kernel Services and Hardware InterfacesKernel Services and Hardware Interface layer in the system model280THE KERNEL SERVICES AND HARDWARE INTERFACE LAYERThe layer boundary also marks the ‘kernel side’ boundary; all components which run in privileged mode in the runtime system are includedwithin the layer.11.2PurposeThe Kernel Services and Hardware Interface layer is the foundational layerof Symbian OS.
It includes the kernel and all the supporting infrastructureneeded to boot and run the kernel on the underlying hardware platform.It is responsible for fundamental operating system services:• bootstrapping the physical or emulated device to provide the basicinitialization of the hardware• creating and managing the fundamental operating system kernelabstractions, for example, threads, processes, memory address spaces,and other resources including timers, mutexes, and so on• scheduling, pre-emption and interrupt handling• access to devices, providing the device-driver framework and devicedrivers that abstract device hardware and implement the two-tierlogical and physical device driver model• encapsulating the kernel–user boundary; all processes which run inprivileged mode originate from this layer• encapsulating the lowest level of an operating system port (‘base port’)to new hardware• insulating all higher layers from actual hardware.The system model collects the kernel and kernel extensions, devicedrivers, and the other hardware abstraction components which arerequired for hardware porting, into a single Kernel Architecture block.(Versions of the system model for Symbian OS v8 have two KernelArchitecture blocks, for each of the EKA1 and EKA2 kernel versions.)Two small collections sit within the layer but outside the block.
Thesecollections each have a single component which is independent of thekernel version but which requires customization in a new port. Thesecomponents implement locale support, which is used by the kernel, andthe screen driver.From Symbian OS v9, the Kernel Architecture block is organizedto reflect the basic architecture of the kernel side of the system, aswell as the recommended structure of a base port.
The kernel includesextensions that implement the device-driver framework, providing a twolayer logical–physical device-driver model in which logical device driversabstract a generic device interface and physical device drivers drivethe actual hardware. Below the kernel, abstraction of device hardwareDESIGN GOALS281is divided between the Application-Specific Standard Part (ASSP), anoff-the-shelf integrated CPU, and the Variant components.
The ASSPcomponent contains ASSP-specific code that is otherwise hardwareagnostic (it supports the specific silicon package used in a product,typically a standard part containing the CPU core and custom chips). TheVariant components contain hardware-dependent code which is specificto a product, for example hardware-specific flash-memory translation.11.3 Design GoalsReleases up to and including Symbian OS v8 shipped with the original kernel, EPOC Kernel Architecture 1 (EKA1). Symbian OS v9 and later releasesship with the new kernel architecture of the EKA2 ‘real-time’ kernel.At the highest level, the design goals of the kernel layer of SymbianOS are common to both kernel versions:• provide an operating system kernel optimized for its device class –palmtop and smaller• optimize for ROM-based execution – XIP- or RAM-shadowed execution• optimize for mobile – no fixed wires• optimize for battery operation – anything from the two ‘AA’ batteriesof the original Psion Series 5 to the latest mobile phone rechargeablebattery• target consumer-oriented devices – for ‘ordinary’ non-technical users.Immediate performance goals follow:• meet the requirements of the device class – in terms of the operatingsystem image size, start-up time, task-loading and task-switchingtimes, its ability to run forever, and overall robustness• meet consumer-device goals – robustness in the face of typical failurescenarios, for example out-of-memory, no signal, low battery orsudden battery removal, media card removed in mid-write, disk fullbut camcorder still running, and so on• provide a highly portable operating system kernel – to enable portingto multiple hardware architectures in as pain-free a way as possible• support typical licensee product models, that is, the product line orproduct family principle – multiple minor hardware revisions followfrom an initial ‘lead product’ and porting effort should scale downsignificantly between a first port and subsequent incremental ports.Compared with the original kernel, EKA2 is explicitly designed tomake porting easier by improving the modularity of the kernel and the282THE KERNEL SERVICES AND HARDWARE INTERFACE LAYERstructuring (and packaging) of its supporting components.
![](https://s.studizba.com/z.php?f=/templates/si/i/noavatar.png&w=100&h=100&t=1"){kind=avatar}
