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<a href='https://github.com/akkartik/mu/blob/main/baremetal/ex3.hex'>https://github.com/akkartik/mu/blob/main/baremetal/ex3.hex</a>
<pre id='vimCodeElement'>
<span id="L1" class="LineNr"> 1 </span><span class="subxComment"># Draw pixels in response to keyboard events, starting from the top-left</span>
<span id="L2" class="LineNr"> 2 </span><span class="subxComment"># and in raster order.</span>
<span id="L3" class="LineNr"> 3 </span><span class="subxComment">#</span>
<span id="L4" class="LineNr"> 4 </span><span class="subxComment"># To run, first prepare a realistically sized disk image:</span>
<span id="L5" class="LineNr"> 5 </span><span class="subxComment"># dd if=/dev/zero of=disk.img count=20160 # 512-byte sectors, so 10MB</span>
<span id="L6" class="LineNr"> 6 </span><span class="subxComment"># Load the program on the disk image:</span>
<span id="L7" class="LineNr"> 7 </span><span class="subxComment"># cat baremetal/boot.hex baremetal/ex3.hex |./bootstrap run apps/hex > a.bin</span>
<span id="L8" class="LineNr"> 8 </span><span class="subxComment"># dd if=a.bin of=disk.img conv=notrunc</span>
<span id="L9" class="LineNr"> 9 </span><span class="subxComment"># To run:</span>
<span id="L10" class="LineNr">10 </span><span class="subxComment"># qemu-system-i386 disk.img</span>
<span id="L11" class="LineNr">11 </span><span class="subxComment"># Or:</span>
<span id="L12" class="LineNr">12 </span><span class="subxComment"># bochs -f baremetal/boot.bochsrc # boot.bochsrc loads disk.img</span>
<span id="L13" class="LineNr">13 </span>
<span id="L14" class="LineNr">14 </span><span class="subxComment"># main: (address 0x9000)</span>
<span id="L15" class="LineNr">15 </span>
<span id="L16" class="LineNr">16 </span><span class="subxComment"># eax <- LFB</span>
<span id="L17" class="LineNr">17 </span>8b <span class="subxComment"># copy *rm32 to r32</span>
<span id="L18" class="LineNr">18 </span> 05 <span class="subxComment"># 00/mod/indirect 000/r32/eax 101/rm32/use-disp32</span>
<span id="L19" class="LineNr">19 </span> 28 7f 00 00 <span class="subxComment"># disp32 [label]</span>
<span id="L20" class="LineNr">20 </span>
<span id="L21" class="LineNr">21 </span><span class="subxComment"># var read index/ecx: byte = 0</span>
<span id="L22" class="LineNr">22 </span>31 c9 <span class="subxComment"># ecx <- xor ecx; 11/direct 001/r32/ecx 001/rm32/ecx</span>
<span id="L23" class="LineNr">23 </span>
<span id="L24" class="LineNr">24 </span><span class="subxComment"># $loop:</span>
<span id="L25" class="LineNr">25 </span> <span class="subxComment"># CL = *read index</span>
<span id="L26" class="LineNr">26 </span> 8a <span class="subxComment"># copy m8 at r32 to r8</span>
<span id="L27" class="LineNr">27 </span> 0d <span class="subxComment"># 00/mod/indirect 001/r8/cl 101/rm32/use-disp32</span>
<span id="L28" class="LineNr">28 </span> cc 7d 00 00 <span class="subxComment"># disp32 [label]</span>
<span id="L29" class="LineNr">29 </span> <span class="subxComment"># CL = *(keyboard buffer + ecx)</span>
<span id="L30" class="LineNr">30 </span> 8a <span class="subxComment"># copy m8 at r32 to r8</span>
<span id="L31" class="LineNr">31 </span> 89 <span class="subxComment"># 10/mod/*+disp32 001/r8/cl 001/rm32/ecx</span>
<span id="L32" class="LineNr">32 </span> d0 7d 00 00 <span class="subxComment"># disp32 [label]</span>
<span id="L33" class="LineNr">33 </span> <span class="subxComment"># if (CL == 0) loop (spin loop)</span>
<span id="L34" class="LineNr">34 </span> 80
<span id="L35" class="LineNr">35 </span> f9 <span class="subxComment"># 11/mod/direct 111/subop/compare 001/rm8/CL</span>
<span id="L36" class="LineNr">36 </span> 00 <span class="subxComment"># imm8</span>
<span id="L37" class="LineNr">37 </span> 74 ef <span class="subxComment"># loop -17 [label]</span>
<span id="L38" class="LineNr">38 </span><span class="subxComment"># offset 0x19:</span>
<span id="L39" class="LineNr">39 </span> <span class="subxComment"># otherwise increment read index</span>
<span id="L40" class="LineNr">40 </span> fe <span class="subxComment"># increment byte</span>
<span id="L41" class="LineNr">41 </span> 05 <span class="subxComment"># 00/mod/indirect 000/subop/increment 101/rm32/use-disp32</span>
<span id="L42" class="LineNr">42 </span> cc 7d 00 00 <span class="subxComment"># disp32 [label]</span>
<span id="L43" class="LineNr">43 </span> <span class="subxComment"># clear top nibble of index (keyboard buffer is circular)</span>
<span id="L44" class="LineNr">44 </span> 80 <span class="subxComment"># and byte</span>
<span id="L45" class="LineNr">45 </span> 25 <span class="subxComment"># 00/mod/indirect 100/subop/and 101/rm32/use-disp32</span>
<span id="L46" class="LineNr">46 </span> cc 7d 00 00 <span class="subxComment"># disp32 [label]</span>
<span id="L47" class="LineNr">47 </span> 0f <span class="subxComment"># imm8</span>
<span id="L48" class="LineNr">48 </span> <span class="subxComment"># print a pixel in fluorescent green</span>
<span id="L49" class="LineNr">49 </span> c6 <span class="subxComment"># copy imm8 to m8 at rm32</span>
<span id="L50" class="LineNr">50 </span> 00 <span class="subxComment"># 00/mod/indirect 000/subop 000/rm32/eax</span>
<span id="L51" class="LineNr">51 </span> 31 <span class="subxComment"># imm32</span>
<span id="L52" class="LineNr">52 </span> 40 <span class="subxComment"># increment eax</span>
<span id="L53" class="LineNr">53 </span> eb dc <span class="subxComment"># loop -36 [label]</span>
<span id="L54" class="LineNr">54 </span>
<span id="L55" class="LineNr">55 </span><span class="subxComment"># $break:</span>
<span id="L56" class="LineNr">56 </span>e9 fb ff ff ff <span class="subxComment"># hang indefinitely</span>
<span id="L57" class="LineNr">57 </span>
<span id="L58" class="LineNr">58 </span><span class="subxComment"># vim:ft=subx</span>
</pre>
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