<!DOCTYPE HTML> <html> <head> <meta http-equiv="Content-Type" content="text/html;charset=US-ASCII"> <meta name="generator" content="ZealOS V1.01"> <style type="text/css"> body {background-color:#fef1f0;} .cF0{color:#000000;background-color:#fef1f0;} .cF1{color:#0148a4;background-color:#fef1f0;} .cF2{color:#3b7901;background-color:#fef1f0;} .cF3{color:#057c7e;background-color:#fef1f0;} .cF4{color:#bb2020;background-color:#fef1f0;} .cF5{color:#9e42ae;background-color:#fef1f0;} .cF6{color:#b57901;background-color:#fef1f0;} .cF7{color:#b2b6af;background-color:#fef1f0;} .cF8{color:#555753;background-color:#fef1f0;} .cF9{color:#678fbb;background-color:#fef1f0;} .cFA{color:#82bc49;background-color:#fef1f0;} .cFB{color:#0097a2;background-color:#fef1f0;} .cFC{color:#e26a6a;background-color:#fef1f0;} .cFD{color:#c671bc;background-color:#fef1f0;} .cFE{color:#c7ab00;background-color:#fef1f0;} .cFF{color:#fef1f0;background-color:#fef1f0;} </style> </head> <body> <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Channel 1 was used historically to refresh the DRAM, but now it is obsolete as the hardware does this itself.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> </html>