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<concept id="GUID-F84E18B8-5883-5A3A-A9DB-EC25BB86149F" xml:lang="en"><title>Timers</title><shortdesc>The Kernel implements timing functions using a 1 millisecond tick

timer.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

<p> The phone hardware must therefore provide a high-speed timer that can

provide regular 1 ms interrupts. The ASSP/Variant part of the base port must

use this timer hardware to call the Kernel every millisecond. </p>

<p>The base port provides the timer service in an interrupt-service routine

called a tick handler. The functions used for this are as follows: </p>

<ul>

<li id="GUID-6CFD0FFF-9D8D-5FBC-867C-88933476D896"><p>The tick handler must

be started by the Variant's implementation of the <xref href="GUID-A83A7C3C-7DC0-3B9C-842F-70FCC751365D.dita#GUID-A83A7C3C-7DC0-3B9C-842F-70FCC751365D/GUID-FE55E398-7F08-384F-9E74-2CC2E45002B6"><apiname>Asic::Init3()</apiname></xref> function. </p> </li>

<li id="GUID-9F148C98-2FA8-529D-A0E8-DB5A4705E063"><p>The tick handler calls

the Kernel's <xref href="GUID-C4EB9F55-9A40-3B4D-B90A-FD39A5E68AE1.dita#GUID-C4EB9F55-9A40-3B4D-B90A-FD39A5E68AE1/GUID-BC7CAC2D-97F2-3B82-AF80-7F8535315052"><apiname>NTImer::TickQ()</apiname></xref> function. </p> </li>

<li id="GUID-DC16C15E-221B-5945-9F5A-349FAD35921D"><p>The Variant reports

the exact number of microseconds between ticks in its implementation of <xref href="GUID-A83A7C3C-7DC0-3B9C-842F-70FCC751365D.dita#GUID-A83A7C3C-7DC0-3B9C-842F-70FCC751365D/GUID-6EAD3751-9F37-3C1B-9910-678A286D80E9"><apiname>Asic::MsTickPeriod()</apiname></xref>. </p> </li>

</ul>

<p>The ASSP/Variant must decide how to implement a repeating tick interrupt

for the hardware available. Typically this involves using either a free running

timer with a match register, which is reset on each match, or a self-reloading

countdown timer, to generate a periodic interrupt. </p>

<p>A base port can implement other timers that are required by peripherals

that have sub-millisecond timing requirements. This is optional, and depends

on the available hardware. </p>

</conbody><related-links>

<link href="GUID-E0DCBDCF-C056-53E5-A375-778327F848E4.dita#GUID-E0DCBDCF-C056-53E5-A375-778327F848E4/GUID-F5275882-BBD0-561F-B617-683AA2004BB9">

<linktext>Asic::Init3()                 implementation</linktext></link>

<link href="http://developer.symbian.org/wiki/index.php/Symbian_OS_Internals/5._Kernel_Services.dita">

<linktext>Symbian OS Internals - Chapter 5.5 Timers</linktext></link>