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<concept id="GUID-2700AAC8-A034-5E7D-B0E0-26B49E68BB18" xml:lang="en"><title>Personality Layer for Real Time Applications</title><shortdesc>A base port can add a software layer called a personality

layer to the Kernel to provide an emulation of a real time operating

system (RTOS)</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

<p>. You can provide a personality layer so that a phone can run existing

protocol stacks, for example, mobile telephony signalling stacks,

or Bluetooth stacks, on the same CPU that runs the Symbian platform

applications. </p>

<p>Such protocol stacks, often referred to as Real Time Applications

(RTA), almost always run on an RTOS, and the aim of the personality

layer is to provide the same API as the RTOS, or at least as much

of it as is required by the RTA. The RTA can then run, using the Kernel

Architecture 2 Nanokernel layer as the underlying real time kernel. </p>

<p>The following diagram illustrates the point simply. </p>

<fig id="GUID-AA5502A3-37BE-5A73-A8D9-1B18DDCC8C96">

<image href="GUID-058FAE44-DF72-53E2-BE62-EDC840A7C87F_d0e25110_href.png" placement="inline"/>

</fig>

<p>There is sample code at <filepath>...\e32\personality\...</filepath> that you should refer to while reading this. </p>

<section id="GUID-D1217729-E0E4-5A02-A02F-524EA9F1D679"><title>RTOS

environment features</title> <p>As a basis for emulating an RTOS,

the RTOS is assumed to provide the following features: </p> <ul>

<li id="GUID-107CEB20-80DA-5AF8-A116-C5FA5E437993"><p>Threads </p> </li>

<li id="GUID-496701DC-E711-5509-B593-5B5A51A7DFC2"><p>Thread synchronisation/communication </p> </li>

<li id="GUID-5ADDB09E-7528-50E0-8661-C64C91AF32CA"><p>Thread scheduling

following a hardware interrupt </p> </li>

<li id="GUID-4856FE5E-95E6-5455-B226-9314071F948E"><p>Timer management

functionality </p> </li>

<li id="GUID-C721F13B-14F9-5E01-9721-19E9475A421B"><p>Memory management. </p> </li>

</ul> <p><b>Threads</b> </p> <p>Threads are independent units of execution,

usually scheduled on a strict highest-priority-first basis. There

are generally a fixed number of priorities. Round robin scheduling

of equal priority threads may be available but is usually not used

in real time applications. Dynamic creation and destruction of threads

may or may not be possible. </p> <p><b>Thread synchronisation/communication</b> </p> <p>Typical examples

of such thread synchronisation and communication mechanisms are semaphores,

message queues and event flags. </p> <p>There is wide variation between

systems as to which primitives are provided and what features they

support. Again, dynamic creation and destruction of such synchronisation

and communication objects may or may not be supported. Mutual exclusion

protection is often achieved by simply disabling interrupts, or occasionally

by disabling rescheduling. </p> <p><b>Thread scheduling following a hardware interrupt</b> </p> <p>This

is usually achieved by allowing interrupt service routines (ISRs)

to make system calls which perform operations such as signalling a

semaphore, posting a message to a queue or setting event flags, which

would cause a thread waiting on the semaphore, message queue or event

flag to run. </p> <p>Some systems don't allow ISRs to perform these

operations directly but require them to queue some kind of deferred

function call. This is a function which runs at a lower priority than

hardware interrupts (i.e. with interrupts enabled) but at a higher

priority than any thread - for example a Nucleus Plus HISR. The deferred

function call then performs the operation which causes thread rescheduling. </p> <p><b>Timer management functionality</b> </p> <p>A timer management

function is usually also provided, allowing several software timers

to be driven from a single hardware timer. On expiry, a software timer

may call a supplied timer handler, post a message to a queue or set

an event flag. </p> <p><b>Memory management</b> </p> <p>An RTOS often provides memory management,

usually in the form of fixed size block management as that allows

real time allocation and deallocation. Some RTOSs may also support

full variable size block management. However most RTOSs do not support

use of a hardware MMU and, even if the RTOS supports it (for example

OSE does), the real time applications under consideration do not make

use of such support since they are generally written to run on hardware

without an MMU. </p> </section>

</conbody></concept>