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  → /design/trunk/src/ch_time.xml @ 130

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Ignore whitespace Rev 130 → Rev 131

/design/trunk/src/ch_time.xml
2,7 → 2,7
<chapter id="time">
<?dbhtml filename="time.html"?>
<title>Time management</title>
<title>Time Management</title>
<para>Time is one of the dimensions in which kernel, as well as the whole
system, operates. It is of special importance to many kernel subsytems.
13,7 → 13,7
to implement timeouting versions of synchronization primitives.</para>
<section>
<title>System clock</title>
<title>System Clock</title>
<para>Every hardware architecture supported by HelenOS must support some
kind of a device that can be programmed to yield periodic time signals
84,7 → 84,7
<para>Kernel subsystems can register a callback function to be executed
with a specified delay. Such a registration is represented by a kernel
structure called <classname>timeout</classname>. Timeouts are registered
via <code>timeout_register()</code> function. This function takes a pointer
via <code>timeout_register</code> function. This function takes a pointer
to a timeout structure, a callback function, a parameter of the callback
function and a delay in microseconds as parameters. After the structure is
initialized with all these values, it is sorted into the processor's list
91,8 → 91,8
of active timeouts, according to the number of clock interrupts remaining
to their expiration and relatively to already listed timeouts.</para>
<para>Timeouts can be unregistered via <code>timeout_unregister()</code>.
This function can, as opposed to <code>timeout_register()</code>, fail when
<para>Timeouts can be unregistered via <code>timeout_unregister</code>.
This function can, as opposed to <code>timeout_register</code>, fail when
it is too late to remove the timeout from the list of active
timeouts.</para>
107,11 → 107,11
</section>
<section>
<title>Generic clock interrupt handler</title>
<title>Generic Clock Interrupt Handler</title>
<para>On each clock interrupt, the architecture specific part of the clock
interrupt handler makes a call to the generic clock interrupt handler
implemented by the <code>clock()</code> function. The generic handler takes
implemented by the <code>clock</code> function. The generic handler takes
care of several mission critical goals:</para>
<itemizedlist>
128,7 → 128,7
</listitem>
</itemizedlist>
<para>The <code>clock()</code> function checks for expired timeouts and
<para>The <code>clock</code> function checks for expired timeouts and
decrements unexpired timeout expiration counters exactly one more times
than is the number of missed clock signals (i.e. at least once and
possibly more times, depending on the missed clock signals counter). The
141,7 → 141,7
</section>
<section>
<title>Time source for userspace</title>
<title>Time Source for Userspace</title>
<para>In HelenOS, userspace tasks don't communicate with the kernel in
order to read the system time. Instead, a mechanism that shares kernel