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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-107AE89E-901E-535F-8D1A-EE347D7822B1" xml:lang="en"><title>Architecture</title><shortdesc>This topic describes the architecture of the Serial Communications+
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Server. </shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>+
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<p>The Serial Communications Server uses the Symbian platform client/server+
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framework. Clients use <codeph>R</codeph> classes that send requests to the+
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Serial Communications Server. The server in turn passes requests to an appropriate+
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plug-in module that handles the particular communication protocol. These plug-in+
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modules are known as <i>Serial Protocol Modules</i> or <i>CSYs</i>. The Serial+
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Protocol Modules are loaded by the Serial Communications server, and are not+
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directly accessed by client applications. A Symbian platform phone may include+
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a number of Serial Protocol Modules as standard, such as for handling RS232+
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and infra-red serial communications. The Serial Protocol Module API allows+
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new Serial Protocol Modules modules to be developed. </p>+
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<p>The Serial Communications Server provides a publishedAll API to access+
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the serial ports of the device. The Serial Communications Server provides+
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functionality such as timeouts and port sharing for all Serial Protocol Modules.+
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The Serial Protocol Modules provide the specific protocol and communicate+
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with the serial device driver. To communicate with the serial device driver,+
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the Serial Protocol Modules use publishedPartner APIs such as <xref href="GUID-3B4E8ED5-72F7-3E51-B188-3C1045526DDF.dita"><apiname>RBusDevComm</apiname></xref>.+
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The <codeph>RBusDevComm</codeph> API provides a handle to a channel to the+
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serial device driver. This device driver only implements the basic data transfer+
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and break operations, and is not intended for use directly by client applications.+
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The device driver is implemented using a Physical Device Driver (PDD) and+
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a Logical Device Driver (LDD). The PDD and LDD must be loaded before a Serial+
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Protocol Module can be used. For a device being tested, the application client+
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may need to load the PDD and LDD. For a device that is shipped, the boot sequence+
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normally loads the LDDs and PDDs. Figure 1 below shows the architecture and+
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the appropriate APIs at each level. Figure 2 below shows the architecture+
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with three Serial Protocol Modules loaded. </p>+
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<fig id="GUID-4F316E33-41C6-5BF4-AAE1-2750C58CC1AA">+
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<title>           Figure 1 - The architecture and the appropriate APIs at+
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each level         </title>+
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<image href="GUID-44ADB485-69C2-5557-AB95-3B6D20870F73_d0e148309_href.png" placement="inline"/>+
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</fig>+
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<fig id="GUID-5B17051E-C4E7-5657-BB62-26072FB13D83">+
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<title>           Figure 2 - The architecture with three CSYs loaded     +
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   </title>+
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<image href="GUID-45DD08DB-FCB3-5546-91B4-25868C8ABAE4_d0e148317_href.png" placement="inline"/>+
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</fig>+
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<p>Each serial port has a limited availability when multiple clients attempt+
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to use the port. The Serial Communications Server provides some functionality+
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to mediate between competing clients. This mediation is provided by the <xref href="GUID-3B4E8ED5-72F7-3E51-B188-3C1045526DDF.dita"><apiname>RComm::Open()</apiname></xref> and <xref href="GUID-3B4E8ED5-72F7-3E51-B188-3C1045526DDF.dita"><apiname>RComm::OpenWithAvailable()</apiname></xref> APIs.+
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However, the first client to access a port has control. If a client must get+
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access to a serial port, then that client must ensure it connects to the serial+
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port before other clients. The reliable method of ensuring access to a serial+
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port is for a client to connect as part of the device boot procedure. If a+
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client must have access to a serial port, then the device manufacturer should+
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specify which clients access ports during device boot. </p>+
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<section id="GUID-39D0A44F-3E6D-486F-BC72-A4260374419C"><title>Historical Notes</title> <ol id="GUID-920828D6-9304-5E44-B82D-671097029B21">+
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<li id="GUID-EE61E2E6-EABB-58D1-AE5A-E452589F5D3C"><p>The framework supplied+
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by the Serial Communications Server for Serial Protocol Modules has a narrower+
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set of capabilities compared to the Socket Server for protocol developers. </p> </li>+
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<li id="GUID-DB979584-6BBE-56AA-8068-FC5650D40A46"><p>In Symbian platform,+
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the Serial Communications Server was converted into a multi-threaded server.+
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The Serial Protocol Modules can be run in separate threads. This change did+
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not change the behaviour of the Serial Communications Server except for three+
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changes: </p> <ol id="GUID-0BCD64C0-448E-5ACA-9928-AC30E42A59CF">+
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<li id="GUID-5EFB6685-D6E8-53D9-B3B6-5E1A944F4247"><p>A serial protocol module+
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which blocks does not stop other Serial Protocol Modules from running </p> </li>+
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<li id="GUID-71E76203-BA35-5854-AC89-E105BEBDB6B3"><p>A serial protocol module+
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can run faster than other modules by changing the configured thread priority </p> </li>+
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<li id="GUID-B844EEB9-B241-553B-8631-622BDA0B7A84"><p>A serial protocol module+
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can use the Serial Communications Server API and request services of another+
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serial protocol module </p> </li>+
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</ol> </li>+
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</ol> </section>+
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</conbody><related-links>+
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<link href="GUID-D0D27AEA-FDDB-5F6F-94F6-ADDF5910DC47.dita"><linktext>        +
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        Client/Server Overview</linktext></link>+
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</related-links></concept>+
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