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<pre style="font-family:monospace;font-size:12pt">
<a name="l1"></a><span class=cF0>The </span><span class=cF2>Programmable Interval Timer</span><span class=cF0> has two purposes: Generate interrupts, and control the </span><span class=cF2>PC speaker</span><span class=cF0>.
<a name="l2"></a>
<a name="l3"></a>It has 3 channels:
<a name="l4"></a></span><span class=cF4>
<a name="l5"></a></span><a href="https://zeal-operating-system.github.io/ZealOS/Kernel/KernelA.HH.html#l686"><span class=cF4>Channel 0</span></a><span class=cF0> can generate an interrupt, IRQ 0, at a defined frequency. We set it up in </span><a href="https://zeal-operating-system.github.io/ZealOS/Kernel/KMain.CC.html#l116"><span class=cF4>TimerInit</span></a><span class=cF0>(), and use it in </span><a href="https://zeal-operating-system.github.io/ZealOS/Kernel/KMisc.CC.html#l22"><span class=cF4>SysTimerRead</span></a><span class=cF0>().
<a name="l6"></a>
<a name="l7"></a>Channel 1 was used historically to refresh the DRAM, but now it is obsolete as the hardware does this itself. Channel 1 is
<a name="l8"></a>useless and might not even be implemented anymore on modern machines.
<a name="l9"></a></span><span class=cF4>
<a name="l10"></a></span><a href="https://zeal-operating-system.github.io/ZealOS/Kernel/KernelA.HH.html#l687"><span class=cF4>Channel 2</span></a><span class=cF0>'s output is connected to the PC speaker.
<a name="l11"></a>
<a name="l12"></a>The Command port is used to control each of these 3 channels. The relevant </span><a href="https://zeal-operating-system.github.io/ZealOS/Kernel/KernelA.HH.html#l690"><span class=cF4>flags</span></a><span class=cF0> are defined.
<a name="l13"></a>
<a name="l14"></a>See </span><a href="https://zeal-operating-system.github.io/ZealOS/Kernel/KMisc.CC.html#l129"><span class=cF4>Sound</span></a><span class=cF0>() for how the PC speaker frequency is changed.</span></pre></body>
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