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<a href='https://github.com/akkartik/mu/blob/main/baremetal/boot.hex'>https://github.com/akkartik/mu/blob/main/baremetal/boot.hex</a>
<pre id='vimCodeElement'>
<span id="L1" class="LineNr"> 1 </span><span class="subxComment"># Code for the first few disk sectors that all programs in this directory need:</span>
<span id="L2" class="LineNr"> 2 </span><span class="subxComment"># - load sectors past the first (using BIOS primitives) since only the first is available by default</span>
<span id="L3" class="LineNr"> 3 </span><span class="subxComment"># - if this fails, print 'D' at top-left of screen and halt</span>
<span id="L4" class="LineNr"> 4 </span><span class="subxComment"># - initialize a minimal graphics mode</span>
<span id="L5" class="LineNr"> 5 </span><span class="subxComment"># - switch to 32-bit mode (giving up access to BIOS primitives)</span>
<span id="L6" class="LineNr"> 6 </span><span class="subxComment"># - set up a handler for keyboard events</span>
<span id="L7" class="LineNr"> 7 </span><span class="subxComment"># - jump to start of program</span>
<span id="L8" class="LineNr"> 8 </span><span class="subxComment">#</span>
<span id="L9" class="LineNr"> 9 </span><span class="subxComment"># To convert to a disk image, first prepare a realistically sized disk image:</span>
<span id="L10" class="LineNr"> 10 </span><span class="subxComment"># dd if=/dev/zero of=disk.img count=20160 # 512-byte sectors, so 10MB</span>
<span id="L11" class="LineNr"> 11 </span><span class="subxComment"># Create initial sectors from this file:</span>
<span id="L12" class="LineNr"> 12 </span><span class="subxComment"># ./bootstrap run apps/hex < baremetal/boot.hex > boot.bin</span>
<span id="L13" class="LineNr"> 13 </span><span class="subxComment"># Translate other sectors into a file called a.img</span>
<span id="L14" class="LineNr"> 14 </span><span class="subxComment"># Load all sectors into the disk image:</span>
<span id="L15" class="LineNr"> 15 </span><span class="subxComment"># cat boot.bin a.img > disk.bin</span>
<span id="L16" class="LineNr"> 16 </span><span class="subxComment"># dd if=disk.bin of=disk.img conv=notrunc</span>
<span id="L17" class="LineNr"> 17 </span><span class="subxComment"># To run:</span>
<span id="L18" class="LineNr"> 18 </span><span class="subxComment"># qemu-system-i386 disk.img</span>
<span id="L19" class="LineNr"> 19 </span><span class="subxComment"># Or:</span>
<span id="L20" class="LineNr"> 20 </span><span class="subxComment"># bochs -f baremetal/boot.bochsrc # boot.bochsrc loads disk.img</span>
<span id="L21" class="LineNr"> 21 </span><span class="subxComment">#</span>
<span id="L22" class="LineNr"> 22 </span><span class="subxComment"># Since we start out in 16-bit mode, we need instructions SubX doesn't</span>
<span id="L23" class="LineNr"> 23 </span><span class="subxComment"># support.</span>
<span id="L24" class="LineNr"> 24 </span><span class="subxComment"># This file contains just lowercase hex bytes and comments. Programming it</span>
<span id="L25" class="LineNr"> 25 </span><span class="subxComment"># requires liberal use of:</span>
<span id="L26" class="LineNr"> 26 </span><span class="subxComment"># - comments documenting expected offsets</span>
<span id="L27" class="LineNr"> 27 </span><span class="subxComment"># - size checks on the emitted file (currently: 6144 bytes)</span>
<span id="L28" class="LineNr"> 28 </span><span class="subxComment"># - xxd to spot-check contents of specific offsets in the generated output</span>
<span id="L29" class="LineNr"> 29 </span><span class="subxComment">#</span>
<span id="L30" class="LineNr"> 30 </span><span class="subxComment"># Programs using this initialization:</span>
<span id="L31" class="LineNr"> 31 </span><span class="subxComment"># - can't use any syscalls</span>
<span id="L32" class="LineNr"> 32 </span><span class="subxComment"># - can't print text to video memory (past these boot sectors)</span>
<span id="L33" class="LineNr"> 33 </span><span class="subxComment"># - must only print raw pixels (256 colors) to video memory (resolution 1024x768)</span>
<span id="L34" class="LineNr"> 34 </span><span class="subxComment"># - must start executing immediately after this file (see outline below)</span>
<span id="L35" class="LineNr"> 35 </span><span class="subxComment">#</span>
<span id="L36" class="LineNr"> 36 </span><span class="subxComment"># Don't panic! This file doesn't contain any loops or function calls. 80% of</span>
<span id="L37" class="LineNr"> 37 </span><span class="subxComment"># it is data. One pass through less than 1KB of code (there's lots of</span>
<span id="L38" class="LineNr"> 38 </span><span class="subxComment"># padding), and then we jump into a better notation. The rest of the stack</span>
<span id="L39" class="LineNr"> 39 </span><span class="subxComment"># (really only in a couple of slightly higher-level places) needs to know just</span>
<span id="L40" class="LineNr"> 40 </span><span class="subxComment"># a few magic constants:</span>
<span id="L41" class="LineNr"> 41 </span><span class="subxComment"># Video memory: start is stored at 0x8128</span>
<span id="L42" class="LineNr"> 42 </span><span class="subxComment"># Keyboard buffer: starts at 0x8028</span>
<span id="L43" class="LineNr"> 43 </span><span class="subxComment">#</span>
<span id="L44" class="LineNr"> 44 </span><span class="subxComment"># No mouse support. _That_ would require panicking.</span>
<span id="L45" class="LineNr"> 45 </span>
<span id="L46" class="LineNr"> 46 </span><span class="subxComment"># Outline of this file with offsets and the addresses they map to at run-time:</span>
<span id="L47" class="LineNr"> 47 </span><span class="subxComment"># -- 16-bit mode code</span>
<span id="L48" class="LineNr"> 48 </span><span class="subxComment"># offset 0 (address 7c00): boot code</span>
<span id="L49" class="LineNr"> 49 </span><span class="subxComment"># -- 16-bit mode data</span>
<span id="L50" class="LineNr"> 50 </span><span class="subxComment"># e0 (address 7c80) global descriptor table</span>
<span id="L51" class="LineNr"> 51 </span><span class="subxComment"># f8 (address 7ca0) <== gdt_descriptor</span>
<span id="L52" class="LineNr"> 52 </span><span class="subxComment"># -- 32-bit mode code</span>
<span id="L53" class="LineNr"> 53 </span><span class="subxComment"># offset 100 (address 7d00): boot code</span>
<span id="L54" class="LineNr"> 54 </span><span class="subxComment"># 1fe (address 7dfe) boot sector marker (2 bytes)</span>
<span id="L55" class="LineNr"> 55 </span><span class="subxComment"># offset 200 (address 7e00): interrupt handler code</span>
<span id="L56" class="LineNr"> 56 </span><span class="subxComment"># -- 32-bit mode data</span>
<span id="L57" class="LineNr"> 57 </span><span class="subxComment"># offset 400 (address 8000): handler data</span>
<span id="L58" class="LineNr"> 58 </span><span class="subxComment"># 410 (address 8010): keyboard handler data</span>
<span id="L59" class="LineNr"> 59 </span><span class="subxComment"># 428 (address 8028) <== keyboard buffer</span>
<span id="L60" class="LineNr"> 60 </span><span class="subxComment"># offset 500 (address 8100): video mode data (256 bytes)</span>
<span id="L61" class="LineNr"> 61 </span><span class="subxComment"># 528 (address 8128) <== start of video RAM stored here</span>
<span id="L62" class="LineNr"> 62 </span><span class="subxComment"># offset 600 (address 8200): interrupt descriptor table (1KB)</span>
<span id="L63" class="LineNr"> 63 </span><span class="subxComment"># offset a00 (address 8600): keyboard mappings (1.5KB)</span>
<span id="L64" class="LineNr"> 64 </span><span class="subxComment"># offset 1000 (address 8c00): bitmap font (2KB)</span>
<span id="L65" class="LineNr"> 65 </span><span class="subxComment"># offset 1800 (address 9400): entrypoint for applications (don't forget to adjust survey_baremetal if this changes)</span>
<span id="L66" class="LineNr"> 66 </span>
<span id="L67" class="LineNr"> 67 </span><span class="subxComment"># Other details of the current memory map:</span>
<span id="L68" class="LineNr"> 68 </span><span class="subxComment"># code: 4 tracks of disk to [0x00007c00, 0x00027400)</span>
<span id="L69" class="LineNr"> 69 </span><span class="subxComment"># stack grows down from 0x00070000</span>
<span id="L70" class="LineNr"> 70 </span><span class="subxComment"># see below</span>
<span id="L71" class="LineNr"> 71 </span><span class="subxComment"># heap: [0x01000000, 0x02000000)</span>
<span id="L72" class="LineNr"> 72 </span><span class="subxComment"># see baremetal/120allocate.subx</span>
<span id="L73" class="LineNr"> 73 </span><span class="subxComment"># Consult <a href="https://wiki.osdev.org/Memory_Map_(x86)">https://wiki.osdev.org/Memory_Map_(x86)</a> before modifying any of this.</span>
<span id="L74" class="LineNr"> 74 </span>
<span id="L75" class="LineNr"> 75 </span><span class="subxComment">## 16-bit entry point</span>
<span id="L76" class="LineNr"> 76 </span>
<span id="L77" class="LineNr"> 77 </span><span class="subxComment"># Upon reset, the IBM PC:</span>
<span id="L78" class="LineNr"> 78 </span><span class="subxComment"># - loads the first sector (512 bytes)</span>
<span id="L79" class="LineNr"> 79 </span><span class="subxComment"># from some bootable image (see the boot sector marker at the end of this file)</span>
<span id="L80" class="LineNr"> 80 </span><span class="subxComment"># to the address range [0x7c00, 0x7e00)</span>
<span id="L81" class="LineNr"> 81 </span><span class="subxComment"># - starts executing code at address 0x7c00</span>
<span id="L82" class="LineNr"> 82 </span>
<span id="L83" class="LineNr"> 83 </span><span class="subxComment"># offset 00 (address 0x7c00):</span>
<span id="L84" class="LineNr"> 84 </span> <span class="subxComment"># disable interrupts for this initialization</span>
<span id="L85" class="LineNr"> 85 </span> fa <span class="subxComment"># cli</span>
<span id="L86" class="LineNr"> 86 </span>
<span id="L87" class="LineNr"> 87 </span> <span class="subxComment"># initialize segment registers</span>
<span id="L88" class="LineNr"> 88 </span> <span class="subxComment"># this isn't always needed, but the recommendation is to not make assumptions</span>
<span id="L89" class="LineNr"> 89 </span> b8 00 00 <span class="subxComment"># ax <- 0</span>
<span id="L90" class="LineNr"> 90 </span> 8e d8 <span class="subxComment"># ds <- ax</span>
<span id="L91" class="LineNr"> 91 </span> 8e c0 <span class="subxComment"># es <- ax</span>
<span id="L92" class="LineNr"> 92 </span> 8e e0 <span class="subxComment"># fs <- ax</span>
<span id="L93" class="LineNr"> 93 </span> 8e e8 <span class="subxComment"># gs <- ax</span>
<span id="L94" class="LineNr"> 94 </span>
<span id="L95" class="LineNr"> 95 </span> <span class="subxComment"># initialize stack to 0x00070000</span>
<span id="L96" class="LineNr"> 96 </span> <span class="subxComment"># We don't read or write the stack before we get to 32-bit mode, but BIOS</span>
<span id="L97" class="LineNr"> 97 </span> <span class="subxComment"># calls do. We need to move the stack in case BIOS initializes it to some</span>
<span id="L98" class="LineNr"> 98 </span> <span class="subxComment"># low address that we want to write code into.</span>
<span id="L99" class="LineNr"> 99 </span> b8 00 70 <span class="subxComment"># ax <- 0x7000</span>
<span id="L100" class="LineNr"> 100 </span> 8e d0 <span class="subxComment"># ss <- ax</span>
<span id="L101" class="LineNr"> 101 </span> bc 00 00 <span class="subxComment"># sp <- 0x0000</span>
<span id="L102" class="LineNr"> 102 </span>
<span id="L103" class="LineNr"> 103 </span><span class="subxComment"># 14:</span>
<span id="L104" class="LineNr"> 104 </span> <span class="subxComment"># load remaining sectors from first two tracks of disk into addresses [0x7e00, 0x17800)</span>
<span id="L105" class="LineNr"> 105 </span> b4 02 <span class="subxComment"># ah <- 2 # read sectors from disk</span>
<span id="L106" class="LineNr"> 106 </span> <span class="subxComment"># dl comes conveniently initialized at boot time with the index of the device being booted</span>
<span id="L107" class="LineNr"> 107 </span> b5 00 <span class="subxComment"># ch <- 0 # cylinder 0</span>
<span id="L108" class="LineNr"> 108 </span> b6 00 <span class="subxComment"># dh <- 0 # track 0</span>
<span id="L109" class="LineNr"> 109 </span> b1 02 <span class="subxComment"># cl <- 2 # second sector, 1-based</span>
<span id="L110" class="LineNr"> 110 </span> b0 7d <span class="subxComment"># al <- 125 # number of sectors to read = 2*63 - 1</span>
<span id="L111" class="LineNr"> 111 </span> <span class="subxComment"># address to write sectors to = es:bx = 0x7e00, contiguous with boot segment</span>
<span id="L112" class="LineNr"> 112 </span> bb 00 00 <span class="subxComment"># bx <- 0</span>
<span id="L113" class="LineNr"> 113 </span> 8e c3 <span class="subxComment"># es <- bx</span>
<span id="L114" class="LineNr"> 114 </span> bb 00 7e <span class="subxComment"># bx <- 0x7e00 [label]</span>
<span id="L115" class="LineNr"> 115 </span> cd 13 <span class="subxComment"># int 13h, BIOS disk service</span>
<span id="L116" class="LineNr"> 116 </span> 0f 82 a3 00 <span class="subxComment"># jump-if-carry disk_error [label]</span>
<span id="L117" class="LineNr"> 117 </span>
<span id="L118" class="LineNr"> 118 </span><span class="subxComment"># 2c:</span>
<span id="L119" class="LineNr"> 119 </span> <span class="subxComment"># load two more tracks of disk into addresses [0x17800, 0x27400)</span>
<span id="L120" class="LineNr"> 120 </span> b4 02 <span class="subxComment"># ah <- 2 # read sectors from disk</span>
<span id="L121" class="LineNr"> 121 </span> <span class="subxComment"># dl comes conveniently initialized at boot time with the index of the device being booted</span>
<span id="L122" class="LineNr"> 122 </span> b5 00 <span class="subxComment"># ch <- 0 # cylinder 0</span>
<span id="L123" class="LineNr"> 123 </span> b6 02 <span class="subxComment"># dh <- 2 # track 0</span>
<span id="L124" class="LineNr"> 124 </span> b1 01 <span class="subxComment"># cl <- 1 # first sector, 1-based</span>
<span id="L125" class="LineNr"> 125 </span> b0 7e <span class="subxComment"># al <- 126 # number of sectors to read = 2*63</span>
<span id="L126" class="LineNr"> 126 </span> <span class="subxComment"># address to write sectors to = es:bx = 0x17800</span>
<span id="L127" class="LineNr"> 127 </span> bb 80 17 <span class="subxComment"># bx <- 0x1780 [label]</span>
<span id="L128" class="LineNr"> 128 </span> 8e c3 <span class="subxComment"># es <- bx</span>
<span id="L129" class="LineNr"> 129 </span> bb 00 00 <span class="subxComment"># bx <- 0</span>
<span id="L130" class="LineNr"> 130 </span> cd 13 <span class="subxComment"># int 13h, BIOS disk service</span>
<span id="L131" class="LineNr"> 131 </span> 0f 82 9b 00 <span class="subxComment"># jump-if-carry disk_error [label]</span>
<span id="L132" class="LineNr"> 132 </span> <span class="subxComment"># reset es</span>
<span id="L133" class="LineNr"> 133 </span> bb 00 00 <span class="subxComment"># bx <- 0</span>
<span id="L134" class="LineNr"> 134 </span> 8e c3 <span class="subxComment"># es <- bx</span>
<span id="L135" class="LineNr"> 135 </span>
<span id="L136" class="LineNr"> 136 </span><span class="subxComment"># 39:</span>
<span id="L137" class="LineNr"> 137 </span> <span class="subxComment"># undo the A20 hack: <a href="https://en.wikipedia.org/wiki/A20_line">https://en.wikipedia.org/wiki/A20_line</a></span>
<span id="L138" class="LineNr"> 138 </span> <span class="subxComment"># this is from <a href="https://github.com/mit-pdos/xv6-public/blob/master/bootasm.S">https://github.com/mit-pdos/xv6-public/blob/master/bootasm.S</a></span>
<span id="L139" class="LineNr"> 139 </span> <span class="subxComment"># seta20.1:</span>
<span id="L140" class="LineNr"> 140 </span> e4 64 <span class="subxComment"># al <- port 0x64</span>
<span id="L141" class="LineNr"> 141 </span> a8 02 <span class="subxComment"># set zf if bit 1 (second-least significant) is not set</span>
<span id="L142" class="LineNr"> 142 </span> 75 fa <span class="subxComment"># if zf not set, goto seta20.1 (-6)</span>
<span id="L143" class="LineNr"> 143 </span>
<span id="L144" class="LineNr"> 144 </span> b0 d1 <span class="subxComment"># al <- 0xd1</span>
<span id="L145" class="LineNr"> 145 </span> e6 64 <span class="subxComment"># port 0x64 <- al</span>
<span id="L146" class="LineNr"> 146 </span>
<span id="L147" class="LineNr"> 147 </span><span class="subxComment"># 43:</span>
<span id="L148" class="LineNr"> 148 </span> <span class="subxComment"># seta20.2:</span>
<span id="L149" class="LineNr"> 149 </span> e4 64 <span class="subxComment"># al <- port 0x64</span>
<span id="L150" class="LineNr"> 150 </span> a8 02 <span class="subxComment"># set zf if bit 1 (second-least significant) is not set</span>
<span id="L151" class="LineNr"> 151 </span> 75 fa <span class="subxComment"># if zf not set, goto seta20.2 (-6)</span>
<span id="L152" class="LineNr"> 152 </span>
<span id="L153" class="LineNr"> 153 </span> b0 df <span class="subxComment"># al <- 0xdf</span>
<span id="L154" class="LineNr"> 154 </span> e6 64 <span class="subxComment"># port 0x64 <- al</span>
<span id="L155" class="LineNr"> 155 </span>
<span id="L156" class="LineNr"> 156 </span><span class="subxComment"># 4d:</span>
<span id="L157" class="LineNr"> 157 </span> <span class="subxComment"># adjust video mode</span>
<span id="L158" class="LineNr"> 158 </span> b4 4f <span class="subxComment"># ah <- 4f (VBE)</span>
<span id="L159" class="LineNr"> 159 </span> b0 02 <span class="subxComment"># al <- 02 (set video mode)</span>
<span id="L160" class="LineNr"> 160 </span> bb 05 41 <span class="subxComment"># bx <- 0x0105 (graphics 1024x768x256</span>
<span id="L161" class="LineNr"> 161 </span> <span class="subxComment"># 0x4000 bit = configure linear frame buffer in Bochs emulator; hopefully this doesn't hurt anything when running natively)</span>
<span id="L162" class="LineNr"> 162 </span> <span class="subxComment"># fallback mode: 0x0101 (640x480x256)</span>
<span id="L163" class="LineNr"> 163 </span> cd 10 <span class="subxComment"># int 10h, Vesa BIOS extensions</span>
<span id="L164" class="LineNr"> 164 </span>
<span id="L165" class="LineNr"> 165 </span><span class="subxComment"># 56:</span>
<span id="L166" class="LineNr"> 166 </span> <span class="subxComment"># load information for the (hopefully) current video mode</span>
<span id="L167" class="LineNr"> 167 </span> <span class="subxComment"># mostly just for the address to the linear frame buffer</span>
<span id="L168" class="LineNr"> 168 </span> b4 4f <span class="subxComment"># ah <- 4f (VBE)</span>
<span id="L169" class="LineNr"> 169 </span> b0 01 <span class="subxComment"># al <- 01 (get video mode info)</span>
<span id="L170" class="LineNr"> 170 </span> b9 07 01 <span class="subxComment"># cx <- 0x0107 (mode we requested)</span>
<span id="L171" class="LineNr"> 171 </span> bf 00 81 <span class="subxComment"># di <- 0x8100 (video mode info) [label]</span>
<span id="L172" class="LineNr"> 172 </span> cd 10
<span id="L173" class="LineNr"> 173 </span>
<span id="L174" class="LineNr"> 174 </span><span class="subxComment"># 62:</span>
<span id="L175" class="LineNr"> 175 </span> <span class="subxComment"># switch to 32-bit mode</span>
<span id="L176" class="LineNr"> 176 </span> 0f 01 16 <span class="subxComment"># lgdt 00/mod/indirect 010/subop 110/rm/use-disp16</span>
<span id="L177" class="LineNr"> 177 </span> f8 7c <span class="subxComment"># *gdt_descriptor [label]</span>
<span id="L178" class="LineNr"> 178 </span> 0f 20 c0 <span class="subxComment"># eax <- cr0</span>
<span id="L179" class="LineNr"> 179 </span> 66 83 c8 01 <span class="subxComment"># eax <- or 0x1</span>
<span id="L180" class="LineNr"> 180 </span> 0f 22 c0 <span class="subxComment"># cr0 <- eax</span>
<span id="L181" class="LineNr"> 181 </span> ea 00 7d 08 00 <span class="subxComment"># far jump to initialize_32bit_mode after setting cs to the record at offset 8 in the gdt (gdt_code) [label]</span>
<span id="L182" class="LineNr"> 182 </span>
<span id="L183" class="LineNr"> 183 </span><span class="subxComment"># padding</span>
<span id="L184" class="LineNr"> 184 </span><span class="subxComment"># 76:</span>
<span id="L185" class="LineNr"> 185 </span> 00 00 00 00 00 00 00 00 00 00
<span id="L186" class="LineNr"> 186 </span>00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L187" class="LineNr"> 187 </span>00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L188" class="LineNr"> 188 </span>00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L189" class="LineNr"> 189 </span>00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L190" class="LineNr"> 190 </span>
<span id="L191" class="LineNr"> 191 </span><span class="subxComment"># cf:</span>
<span id="L192" class="LineNr"> 192 </span><span class="subxComment"># disk_error:</span>
<span id="L193" class="LineNr"> 193 </span> <span class="subxComment"># print 'D' to top-left of screen to indicate disk error</span>
<span id="L194" class="LineNr"> 194 </span> <span class="subxComment"># *0xb8000 <- 0x0f44</span>
<span id="L195" class="LineNr"> 195 </span> <span class="subxComment"># bx <- 0xb800</span>
<span id="L196" class="LineNr"> 196 </span> bb 00 b8
<span id="L197" class="LineNr"> 197 </span> <span class="subxComment"># ds <- bx</span>
<span id="L198" class="LineNr"> 198 </span> 8e db <span class="subxComment"># 11b/mod 011b/reg/ds 011b/rm/bx</span>
<span id="L199" class="LineNr"> 199 </span> <span class="subxComment"># al <- 'D'</span>
<span id="L200" class="LineNr"> 200 </span> b0 44
<span id="L201" class="LineNr"> 201 </span> <span class="subxComment"># ah <- 0x0f # white on black</span>
<span id="L202" class="LineNr"> 202 </span> b4 0f
<span id="L203" class="LineNr"> 203 </span> <span class="subxComment"># bx <- 0</span>
<span id="L204" class="LineNr"> 204 </span> bb 00 00
<span id="L205" class="LineNr"> 205 </span> <span class="subxComment"># *ds:bx <- ax</span>
<span id="L206" class="LineNr"> 206 </span> 89 07 <span class="subxComment"># 00b/mod/indirect 000b/reg/ax 111b/rm/bx</span>
<span id="L207" class="LineNr"> 207 </span>
<span id="L208" class="LineNr"> 208 </span>e9 fd ff <span class="subxComment"># loop forever</span>
<span id="L209" class="LineNr"> 209 </span>
<span id="L210" class="LineNr"> 210 </span><span class="subxComment">## GDT: 3 records of 8 bytes each</span>
<span id="L211" class="LineNr"> 211 </span>
<span id="L212" class="LineNr"> 212 </span><span class="subxComment"># e0:</span>
<span id="L213" class="LineNr"> 213 </span><span class="subxComment"># gdt_start:</span>
<span id="L214" class="LineNr"> 214 </span><span class="subxComment"># gdt_null: mandatory null descriptor</span>
<span id="L215" class="LineNr"> 215 </span> 00 00 00 00 00 00 00 00
<span id="L216" class="LineNr"> 216 </span><span class="subxComment"># gdt_code: (offset 8 from gdt_start)</span>
<span id="L217" class="LineNr"> 217 </span> ff ff <span class="subxComment"># limit[0:16]</span>
<span id="L218" class="LineNr"> 218 </span> 00 00 00 <span class="subxComment"># base[0:24]</span>
<span id="L219" class="LineNr"> 219 </span> 9a <span class="subxComment"># 1/present 00/privilege 1/descriptor type = 1001b</span>
<span id="L220" class="LineNr"> 220 </span> <span class="subxComment"># 1/code 0/conforming 1/readable 0/accessed = 1010b</span>
<span id="L221" class="LineNr"> 221 </span> cf <span class="subxComment"># 1/granularity 1/32-bit 0/64-bit-segment 0/AVL = 1100b</span>
<span id="L222" class="LineNr"> 222 </span> <span class="subxComment"># limit[16:20] = 1111b</span>
<span id="L223" class="LineNr"> 223 </span> 00 <span class="subxComment"># base[24:32]</span>
<span id="L224" class="LineNr"> 224 </span><span class="subxComment"># gdt_data: (offset 16 from gdt_start)</span>
<span id="L225" class="LineNr"> 225 </span> ff ff <span class="subxComment"># limit[0:16]</span>
<span id="L226" class="LineNr"> 226 </span> 00 00 00 <span class="subxComment"># base[0:24]</span>
<span id="L227" class="LineNr"> 227 </span> 92 <span class="subxComment"># 1/present 00/privilege 1/descriptor type = 1001b</span>
<span id="L228" class="LineNr"> 228 </span> <span class="subxComment"># 0/data 0/conforming 1/readable 0/accessed = 0010b</span>
<span id="L229" class="LineNr"> 229 </span> cf <span class="subxComment"># same as gdt_code</span>
<span id="L230" class="LineNr"> 230 </span> 00 <span class="subxComment"># base[24:32]</span>
<span id="L231" class="LineNr"> 231 </span><span class="subxComment"># gdt_end:</span>
<span id="L232" class="LineNr"> 232 </span>
<span id="L233" class="LineNr"> 233 </span><span class="subxComment"># f8:</span>
<span id="L234" class="LineNr"> 234 </span><span class="subxComment"># gdt_descriptor:</span>
<span id="L235" class="LineNr"> 235 </span> 17 00 <span class="subxComment"># final index of gdt = gdt_end - gdt_start - 1</span>
<span id="L236" class="LineNr"> 236 </span> e0 7c 00 00 <span class="subxComment"># start = gdt_start [label]</span>
<span id="L237" class="LineNr"> 237 </span>
<span id="L238" class="LineNr"> 238 </span><span class="subxComment"># padding</span>
<span id="L239" class="LineNr"> 239 </span><span class="subxComment"># fe:</span>
<span id="L240" class="LineNr"> 240 </span> 00 00
<span id="L241" class="LineNr"> 241 </span>
<span id="L242" class="LineNr"> 242 </span><span class="subxComment">## 32-bit code from this point (still some instructions not in SubX)</span>
<span id="L243" class="LineNr"> 243 </span>
<span id="L244" class="LineNr"> 244 </span><span class="subxComment"># offset 100 (address 0x7d00):</span>
<span id="L245" class="LineNr"> 245 </span><span class="subxComment"># initialize_32bit_mode:</span>
<span id="L246" class="LineNr"> 246 </span> 66 b8 10 00 <span class="subxComment"># ax <- offset 16 from gdt_start</span>
<span id="L247" class="LineNr"> 247 </span> 8e d8 <span class="subxComment"># ds <- ax</span>
<span id="L248" class="LineNr"> 248 </span> 8e d0 <span class="subxComment"># ss <- ax</span>
<span id="L249" class="LineNr"> 249 </span> 8e c0 <span class="subxComment"># es <- ax</span>
<span id="L250" class="LineNr"> 250 </span> 8e e0 <span class="subxComment"># fs <- ax</span>
<span id="L251" class="LineNr"> 251 </span> 8e e8 <span class="subxComment"># gs <- ax</span>
<span id="L252" class="LineNr"> 252 </span>
<span id="L253" class="LineNr"> 253 </span><span class="subxComment"># 10e:</span>
<span id="L254" class="LineNr"> 254 </span> bc 00 00 07 00 <span class="subxComment"># esp <- 0x00070000</span>
<span id="L255" class="LineNr"> 255 </span>
<span id="L256" class="LineNr"> 256 </span><span class="subxComment"># 113:</span>
<span id="L257" class="LineNr"> 257 </span> <span class="subxComment"># load interrupt handlers</span>
<span id="L258" class="LineNr"> 258 </span> 0f 01 1d <span class="subxComment"># lidt 00/mod/indirect 011/subop 101/rm32/use-disp32</span>
<span id="L259" class="LineNr"> 259 </span> 00 80 00 00 <span class="subxComment"># *idt_descriptor [label]</span>
<span id="L260" class="LineNr"> 260 </span>
<span id="L261" class="LineNr"> 261 </span> <span class="subxComment"># For now, not bothering reprogramming the IRQ to not conflict with software</span>
<span id="L262" class="LineNr"> 262 </span> <span class="subxComment"># exceptions.</span>
<span id="L263" class="LineNr"> 263 </span> <span class="subxComment"># <a href="https://wiki.osdev.org/index.php?title=8259_PIC&oldid=24650#Protected_Mode">https://wiki.osdev.org/index.php?title=8259_PIC&oldid=24650#Protected_Mode</a></span>
<span id="L264" class="LineNr"> 264 </span> <span class="subxComment">#</span>
<span id="L265" class="LineNr"> 265 </span> <span class="subxComment"># Interrupt 1 (keyboard) conflicts with debugger faults. We don't use a</span>
<span id="L266" class="LineNr"> 266 </span> <span class="subxComment"># debugger.</span>
<span id="L267" class="LineNr"> 267 </span> <span class="subxComment"># Reference:</span>
<span id="L268" class="LineNr"> 268 </span> <span class="subxComment"># <a href="https://wiki.osdev.org/Exceptions">https://wiki.osdev.org/Exceptions</a></span>
<span id="L269" class="LineNr"> 269 </span>
<span id="L270" class="LineNr"> 270 </span><span class="subxComment"># 11a:</span>
<span id="L271" class="LineNr"> 271 </span> <span class="subxComment"># enable keyboard IRQ (1)</span>
<span id="L272" class="LineNr"> 272 </span> b0 fd <span class="subxComment"># al <- 0xfd # disable mask for IRQ1</span>
<span id="L273" class="LineNr"> 273 </span> e6 21 <span class="subxComment"># port 0x21 <- al</span>
<span id="L274" class="LineNr"> 274 </span>
<span id="L275" class="LineNr"> 275 </span><span class="subxComment"># 11e:</span>
<span id="L276" class="LineNr"> 276 </span> fb <span class="subxComment"># enable interrupts</span>
<span id="L277" class="LineNr"> 277 </span> db e3 <span class="subxComment"># initialize FPU</span>
<span id="L278" class="LineNr"> 278 </span> <span class="subxComment"># eax <- cr4</span>
<span id="L279" class="LineNr"> 279 </span> 0f 20 <span class="subxComment"># copy cr4 to rm32</span>
<span id="L280" class="LineNr"> 280 </span> e0 <span class="subxComment"># 11/mod/direct 100/r32/CR4 000/rm32/eax</span>
<span id="L281" class="LineNr"> 281 </span> <span class="subxComment"># eax <- or bit 9</span>
<span id="L282" class="LineNr"> 282 </span> 0f ba
<span id="L283" class="LineNr"> 283 </span> e8 <span class="subxComment"># 11/mod/direct 101/subop/bit-test-and-set 000/rm32/eax</span>
<span id="L284" class="LineNr"> 284 </span> 09 <span class="subxComment"># imm8</span>
<span id="L285" class="LineNr"> 285 </span> <span class="subxComment"># cr4 <- eax</span>
<span id="L286" class="LineNr"> 286 </span> 0f 22 <span class="subxComment"># copy rm32 to cr4</span>
<span id="L287" class="LineNr"> 287 </span> e0 <span class="subxComment"># 11/mod/direct 100/r32/CR4 000/rm32/eax</span>
<span id="L288" class="LineNr"> 288 </span> e9 d0 16 00 00 <span class="subxComment"># jump to 0x9400 [label]</span>
<span id="L289" class="LineNr"> 289 </span>
<span id="L290" class="LineNr"> 290 </span><span class="subxComment"># padding</span>
<span id="L291" class="LineNr"> 291 </span><span class="subxComment"># 130:</span>
<span id="L292" class="LineNr"> 292 </span>00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L293" class="LineNr"> 293 </span>00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L294" class="LineNr"> 294 </span>00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L295" class="LineNr"> 295 </span>00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L296" class="LineNr"> 296 </span>00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L297" class="LineNr"> 297 </span>00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L298" class="LineNr"> 298 </span>00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L299" class="LineNr"> 299 </span>00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L300" class="LineNr"> 300 </span>00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L301" class="LineNr"> 301 </span>00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L302" class="LineNr"> 302 </span>00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L303" class="LineNr"> 303 </span>00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L304" class="LineNr"> 304 </span>00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L305" class="LineNr"> 305 </span>
<span id="L306" class="LineNr"> 306 </span><span class="subxComment"># 1fe:</span>
<span id="L307" class="LineNr"> 307 </span><span class="subxComment"># final 2 bytes of boot sector</span>
<span id="L308" class="LineNr"> 308 </span>55 aa
<span id="L309" class="LineNr"> 309 </span>
<span id="L310" class="LineNr"> 310 </span><span class="subxComment">## sector 2 onwards loaded by load_disk, not automatically on boot</span>
<span id="L311" class="LineNr"> 311 </span>
<span id="L312" class="LineNr"> 312 </span><span class="subxComment"># offset 200 (address 0x7e00):</span>
<span id="L313" class="LineNr"> 313 </span><span class="subxComment"># null interrupt handler:</span>
<span id="L314" class="LineNr"> 314 </span> cf <span class="subxComment"># iret</span>
<span id="L315" class="LineNr"> 315 </span>
<span id="L316" class="LineNr"> 316 </span><span class="subxComment"># padding</span>
<span id="L317" class="LineNr"> 317 </span><span class="subxComment"># 201:</span>
<span id="L318" class="LineNr"> 318 </span> 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L319" class="LineNr"> 319 </span>
<span id="L320" class="LineNr"> 320 </span><span class="subxComment"># 210:</span>
<span id="L321" class="LineNr"> 321 </span><span class="subxComment"># keyboard interrupt handler:</span>
<span id="L322" class="LineNr"> 322 </span> <span class="subxComment"># prologue</span>
<span id="L323" class="LineNr"> 323 </span> fa <span class="subxComment"># disable interrupts</span>
<span id="L324" class="LineNr"> 324 </span> 60 <span class="subxComment"># push all registers to stack</span>
<span id="L325" class="LineNr"> 325 </span> <span class="subxComment"># acknowledge interrupt</span>
<span id="L326" class="LineNr"> 326 </span> b0 20 <span class="subxComment"># al <- 0x20</span>
<span id="L327" class="LineNr"> 327 </span> e6 20 <span class="subxComment"># port 0x20 <- al</span>
<span id="L328" class="LineNr"> 328 </span> 31 c0 <span class="subxComment"># eax <- xor eax; 11/direct 000/r32/eax 000/rm32/eax</span>
<span id="L329" class="LineNr"> 329 </span> <span class="subxComment"># check output buffer of 8042 keyboard controller (<a href="https://web.archive.org/web/20040604041507/http://panda.cs.ndsu.nodak.edu/~achapwes/PICmicro/keyboard/atkeyboard.html">https://web.archive.org/web/20040604041507/http://panda.cs.ndsu.nodak.edu/~achapwes/PICmicro/keyboard/atkeyboard.html</a>)</span>
<span id="L330" class="LineNr"> 330 </span> e4 64 <span class="subxComment"># al <- port 0x64</span>
<span id="L331" class="LineNr"> 331 </span> a8 01 <span class="subxComment"># set zf if bit 0 (least significant) is not set</span>
<span id="L332" class="LineNr"> 332 </span> 74 89 <span class="subxComment"># jump to epilogue if 0 bit is not set [label]</span>
<span id="L333" class="LineNr"> 333 </span><span class="subxComment"># 21e:</span>
<span id="L334" class="LineNr"> 334 </span> <span class="subxH1Comment"># - if keyboard buffer is full, return</span>
<span id="L335" class="LineNr"> 335 </span> 31 c9 <span class="subxComment"># ecx <- xor ecx; 11/direct 001/r32/ecx 001/rm32/ecx</span>
<span id="L336" class="LineNr"> 336 </span> <span class="subxComment"># var index/ecx: byte</span>
<span id="L337" class="LineNr"> 337 </span> 8a <span class="subxComment"># copy m8 at r32 to r8</span>
<span id="L338" class="LineNr"> 338 </span> 0d <span class="subxComment"># 00/mod/indirect 001/r8/cl 101/rm32/use-disp32</span>
<span id="L339" class="LineNr"> 339 </span> 28 80 00 00 <span class="subxComment"># disp32 [label]</span>
<span id="L340" class="LineNr"> 340 </span> <span class="subxComment"># al = *(keyboard buffer + index)</span>
<span id="L341" class="LineNr"> 341 </span> 8a <span class="subxComment"># copy m8 at r32 to r8</span>
<span id="L342" class="LineNr"> 342 </span> 81 <span class="subxComment"># 10/mod/*+disp32 000/r8/al 001/rm32/ecx</span>
<span id="L343" class="LineNr"> 343 </span> 30 80 00 00 <span class="subxComment"># disp32 [label]</span>
<span id="L344" class="LineNr"> 344 </span> <span class="subxComment"># if (al != 0) return</span>
<span id="L345" class="LineNr"> 345 </span> 3c 00 <span class="subxComment"># compare al, 0</span>
<span id="L346" class="LineNr"> 346 </span> 75 77 <span class="subxComment"># jump to epilogue if != [label]</span>
<span id="L347" class="LineNr"> 347 </span><span class="subxComment"># 230:</span>
<span id="L348" class="LineNr"> 348 </span> <span class="subxH1Comment"># - read keycode</span>
<span id="L349" class="LineNr"> 349 </span> e4 60 <span class="subxComment"># al <- port 0x60</span>
<span id="L350" class="LineNr"> 350 </span> <span class="subxH1Comment"># - key released</span>
<span id="L351" class="LineNr"> 351 </span> <span class="subxComment"># if (al == 0xaa) shift = false # left shift is being lifted</span>
<span id="L352" class="LineNr"> 352 </span> 3c aa <span class="subxComment"># compare al, 0xaa</span>
<span id="L353" class="LineNr"> 353 </span> 75 0a <span class="subxComment"># jump to $1 if != [label]</span>
<span id="L354" class="LineNr"> 354 </span> <span class="subxComment"># *shift = 0</span>
<span id="L355" class="LineNr"> 355 </span> c7 <span class="subxComment"># copy imm32 to rm32</span>
<span id="L356" class="LineNr"> 356 </span> 05 <span class="subxComment"># 00/mod/indirect 000/subop/copy 101/rm32/use-disp32</span>
<span id="L357" class="LineNr"> 357 </span> 10 80 00 00 <span class="subxComment"># disp32 [label]</span>
<span id="L358" class="LineNr"> 358 </span> 00 00 00 00 <span class="subxComment"># imm32</span>
<span id="L359" class="LineNr"> 359 </span><span class="subxComment"># 240:</span>
<span id="L360" class="LineNr"> 360 </span><span class="subxComment"># $1:</span>
<span id="L361" class="LineNr"> 361 </span> <span class="subxComment"># if (al == 0xb6) shift = false # right shift is being lifted</span>
<span id="L362" class="LineNr"> 362 </span> 3c b6 <span class="subxComment"># compare al, 0xb6</span>
<span id="L363" class="LineNr"> 363 </span> 75 0a <span class="subxComment"># jump to $1 if != [label]</span>
<span id="L364" class="LineNr"> 364 </span> <span class="subxComment"># *shift = 0</span>
<span id="L365" class="LineNr"> 365 </span> c7 <span class="subxComment"># copy imm32 to rm32</span>
<span id="L366" class="LineNr"> 366 </span> 05 <span class="subxComment"># 00/mod/indirect 000/subop/copy 101/rm32/use-disp32</span>
<span id="L367" class="LineNr"> 367 </span> 10 80 00 00 <span class="subxComment"># disp32 [label]</span>
<span id="L368" class="LineNr"> 368 </span> 00 00 00 00 <span class="subxComment"># imm32</span>
<span id="L369" class="LineNr"> 369 </span><span class="subxComment"># $2:</span>
<span id="L370" class="LineNr"> 370 </span> <span class="subxComment"># if (al & 0x80) a key is being lifted; return</span>
<span id="L371" class="LineNr"> 371 </span> 50 <span class="subxComment"># push eax</span>
<span id="L372" class="LineNr"> 372 </span> 24 80 <span class="subxComment"># al <- and 0x80</span>
<span id="L373" class="LineNr"> 373 </span> 3c 00 <span class="subxComment"># compare al, 0</span>
<span id="L374" class="LineNr"> 374 </span> 58 <span class="subxComment"># pop to eax (without touching flags)</span>
<span id="L375" class="LineNr"> 375 </span> 75 51 <span class="subxComment"># jump to epilogue if != [label]</span>
<span id="L376" class="LineNr"> 376 </span><span class="subxComment"># 256:</span>
<span id="L377" class="LineNr"> 377 </span> <span class="subxH1Comment"># - key pressed</span>
<span id="L378" class="LineNr"> 378 </span> <span class="subxComment"># if (al == 0x2a) shift = true, return # left shift pressed</span>
<span id="L379" class="LineNr"> 379 </span> 3c 2a <span class="subxComment"># compare al, 0x2a</span>
<span id="L380" class="LineNr"> 380 </span> 75 0c <span class="subxComment"># jump to $3 if != [label]</span>
<span id="L381" class="LineNr"> 381 </span> <span class="subxComment"># *shift = 1</span>
<span id="L382" class="LineNr"> 382 </span> c7 <span class="subxComment"># copy imm32 to rm32</span>
<span id="L383" class="LineNr"> 383 </span> 05 <span class="subxComment"># 00/mod/indirect 000/subop/copy 101/rm32/use-disp32</span>
<span id="L384" class="LineNr"> 384 </span> 10 80 00 00 <span class="subxComment"># disp32 [label]</span>
<span id="L385" class="LineNr"> 385 </span> 01 00 00 00 <span class="subxComment"># imm32</span>
<span id="L386" class="LineNr"> 386 </span> eb 41 <span class="subxComment"># jump to epilogue [label]</span>
<span id="L387" class="LineNr"> 387 </span><span class="subxComment"># 266:</span>
<span id="L388" class="LineNr"> 388 </span><span class="subxComment"># $3:</span>
<span id="L389" class="LineNr"> 389 </span> <span class="subxComment"># if (al == 0x36) shift = true, return # right shift pressed</span>
<span id="L390" class="LineNr"> 390 </span> 3c 36 <span class="subxComment"># compare al, 0x36</span>
<span id="L391" class="LineNr"> 391 </span> 75 0c <span class="subxComment"># jump to $4 if != [label]</span>
<span id="L392" class="LineNr"> 392 </span> <span class="subxComment"># *shift = 1</span>
<span id="L393" class="LineNr"> 393 </span> c7 <span class="subxComment"># copy imm32 to rm32</span>
<span id="L394" class="LineNr"> 394 </span> 05 <span class="subxComment"># 00/mod/indirect 000/subop/copy 101/rm32/use-disp32</span>
<span id="L395" class="LineNr"> 395 </span> 10 80 00 00 <span class="subxComment"># disp32 [label]</span>
<span id="L396" class="LineNr"> 396 </span> 01 00 00 00 <span class="subxComment"># imm32</span>
<span id="L397" class="LineNr"> 397 </span> eb 31 <span class="subxComment"># jump to epilogue [label]</span>
<span id="L398" class="LineNr"> 398 </span><span class="subxComment"># 276:</span>
<span id="L399" class="LineNr"> 399 </span><span class="subxComment"># $4:</span>
<span id="L400" class="LineNr"> 400 </span> <span class="subxH1Comment"># - convert key to character</span>
<span id="L401" class="LineNr"> 401 </span> <span class="subxComment"># if (shift) use keyboard normal map</span>
<span id="L402" class="LineNr"> 402 </span> 81 <span class="subxComment"># operate on rm32 and imm32</span>
<span id="L403" class="LineNr"> 403 </span> 3d <span class="subxComment"># 00/mod/indirect 111/subop/compare 101/rm32/use-disp32</span>
<span id="L404" class="LineNr"> 404 </span> 10 80 00 00 <span class="subxComment"># disp32 = shift [label]</span>
<span id="L405" class="LineNr"> 405 </span> 00 00 00 00 <span class="subxComment"># imm32</span>
<span id="L406" class="LineNr"> 406 </span> 74 08 <span class="subxComment"># jump to $5 if = [label]</span>
<span id="L407" class="LineNr"> 407 </span> <span class="subxComment"># otherwise use keyboard shift map</span>
<span id="L408" class="LineNr"> 408 </span> <span class="subxComment"># al <- *(keyboard shift map + eax)</span>
<span id="L409" class="LineNr"> 409 </span> 8a <span class="subxComment"># copy m8 at rm32 to r8</span>
<span id="L410" class="LineNr"> 410 </span> 80 <span class="subxComment"># 10/mod/*+disp32 000/r8/al 000/rm32/eax</span>
<span id="L411" class="LineNr"> 411 </span> 00 87 00 00 <span class="subxComment"># disp32 [label]</span>
<span id="L412" class="LineNr"> 412 </span> eb 06 <span class="subxComment"># jump to $6 [label]</span>
<span id="L413" class="LineNr"> 413 </span><span class="subxComment"># 28a:</span>
<span id="L414" class="LineNr"> 414 </span><span class="subxComment"># $5:</span>
<span id="L415" class="LineNr"> 415 </span> <span class="subxComment"># al <- *(keyboard normal map + eax)</span>
<span id="L416" class="LineNr"> 416 </span> 8a <span class="subxComment"># copy m8 at rm32 to r8</span>
<span id="L417" class="LineNr"> 417 </span> 80 <span class="subxComment"># 10/mod/*+disp32 000/r8/al 000/rm32/eax</span>
<span id="L418" class="LineNr"> 418 </span> 00 86 00 00 <span class="subxComment"># disp32 [label]</span>
<span id="L419" class="LineNr"> 419 </span><span class="subxComment"># $6:</span>
<span id="L420" class="LineNr"> 420 </span> <span class="subxH1Comment"># - if there's no character mapping, return</span>
<span id="L421" class="LineNr"> 421 </span> 3c 00 <span class="subxComment"># compare al, 0</span>
<span id="L422" class="LineNr"> 422 </span> 74 13 <span class="subxComment"># jump to epilogue if = [label]</span>
<span id="L423" class="LineNr"> 423 </span><span class="subxComment"># 294:</span>
<span id="L424" class="LineNr"> 424 </span> <span class="subxH1Comment"># - store al in keyboard buffer</span>
<span id="L425" class="LineNr"> 425 </span> 88 <span class="subxComment"># copy r8 to m8 at r32</span>
<span id="L426" class="LineNr"> 426 </span> 81 <span class="subxComment"># 10/mod/*+disp32 000/r8/al 001/rm32/ecx</span>
<span id="L427" class="LineNr"> 427 </span> 30 80 00 00 <span class="subxComment"># disp32 [label]</span>
<span id="L428" class="LineNr"> 428 </span> <span class="subxComment"># increment index</span>
<span id="L429" class="LineNr"> 429 </span> fe <span class="subxComment"># increment byte</span>
<span id="L430" class="LineNr"> 430 </span> 05 <span class="subxComment"># 00/mod/indirect 000/subop/increment 101/rm32/use-disp32</span>
<span id="L431" class="LineNr"> 431 </span> 28 80 00 00 <span class="subxComment"># disp32 [label]</span>
<span id="L432" class="LineNr"> 432 </span> <span class="subxComment"># clear top nibble of index (keyboard buffer is circular)</span>
<span id="L433" class="LineNr"> 433 </span> 80 <span class="subxComment"># and byte</span>
<span id="L434" class="LineNr"> 434 </span> 25 <span class="subxComment"># 00/mod/indirect 100/subop/and 101/rm32/use-disp32</span>
<span id="L435" class="LineNr"> 435 </span> 28 80 00 00 <span class="subxComment"># disp32 [label]</span>
<span id="L436" class="LineNr"> 436 </span> 0f <span class="subxComment"># imm8</span>
<span id="L437" class="LineNr"> 437 </span><span class="subxComment"># 2a9:</span>
<span id="L438" class="LineNr"> 438 </span> <span class="subxComment"># epilogue</span>
<span id="L439" class="LineNr"> 439 </span> 61 <span class="subxComment"># pop all registers</span>
<span id="L440" class="LineNr"> 440 </span> fb <span class="subxComment"># enable interrupts</span>
<span id="L441" class="LineNr"> 441 </span> cf <span class="subxComment"># iret</span>
<span id="L442" class="LineNr"> 442 </span>
<span id="L443" class="LineNr"> 443 </span><span class="subxComment"># padding</span>
<span id="L444" class="LineNr"> 444 </span><span class="subxComment"># 2aa:</span>
<span id="L445" class="LineNr"> 445 </span> 00 00 00 00 00 00
<span id="L446" class="LineNr"> 446 </span>00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L447" class="LineNr"> 447 </span>00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L448" class="LineNr"> 448 </span>00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L449" class="LineNr"> 449 </span>00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L450" class="LineNr"> 450 </span>00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L451" class="LineNr"> 451 </span><span class="subxComment"># 300:</span>
<span id="L452" class="LineNr"> 452 </span>00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L453" class="LineNr"> 453 </span>00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L454" class="LineNr"> 454 </span>00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L455" class="LineNr"> 455 </span>00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L456" class="LineNr"> 456 </span>00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L457" class="LineNr"> 457 </span>00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L458" class="LineNr"> 458 </span>00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L459" class="LineNr"> 459 </span>00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L460" class="LineNr"> 460 </span>00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L461" class="LineNr"> 461 </span>00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L462" class="LineNr"> 462 </span>00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L463" class="LineNr"> 463 </span>00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L464" class="LineNr"> 464 </span>00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L465" class="LineNr"> 465 </span>00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L466" class="LineNr"> 466 </span>00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L467" class="LineNr"> 467 </span>00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L468" class="LineNr"> 468 </span>
<span id="L469" class="LineNr"> 469 </span><span class="subxComment"># offset 400 (address 0x8000): interrupt handler data</span>
<span id="L470" class="LineNr"> 470 </span><span class="subxComment"># idt_descriptor:</span>
<span id="L471" class="LineNr"> 471 </span> ff 03 <span class="subxComment"># idt_end - idt_start - 1</span>
<span id="L472" class="LineNr"> 472 </span> 00 82 00 00 <span class="subxComment"># start = idt_start [label]</span>
<span id="L473" class="LineNr"> 473 </span>
<span id="L474" class="LineNr"> 474 </span><span class="subxComment"># padding</span>
<span id="L475" class="LineNr"> 475 </span><span class="subxComment"># 406:</span>
<span id="L476" class="LineNr"> 476 </span> 00 00 00 00 00 00 00 00 00 00
<span id="L477" class="LineNr"> 477 </span>
<span id="L478" class="LineNr"> 478 </span><span class="subxComment"># 410:</span>
<span id="L479" class="LineNr"> 479 </span><span class="subxComment"># var shift: boolean</span>
<span id="L480" class="LineNr"> 480 </span> 00 00 00 00
<span id="L481" class="LineNr"> 481 </span>
<span id="L482" class="LineNr"> 482 </span><span class="subxComment"># padding</span>
<span id="L483" class="LineNr"> 483 </span><span class="subxComment"># 414:</span>
<span id="L484" class="LineNr"> 484 </span> 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L485" class="LineNr"> 485 </span>00 00 00 00 00 00 00 00
<span id="L486" class="LineNr"> 486 </span>
<span id="L487" class="LineNr"> 487 </span><span class="subxComment"># 428:</span>
<span id="L488" class="LineNr"> 488 </span><span class="subxComment"># var keyboard circular buffer</span>
<span id="L489" class="LineNr"> 489 </span><span class="subxComment"># write index: nibble</span>
<span id="L490" class="LineNr"> 490 </span><span class="subxComment"># still take up 4 bytes so SubX can handle it</span>
<span id="L491" class="LineNr"> 491 </span> 00 00 00 00
<span id="L492" class="LineNr"> 492 </span><span class="subxComment"># 42c:</span>
<span id="L493" class="LineNr"> 493 </span><span class="subxComment"># read index: nibble</span>
<span id="L494" class="LineNr"> 494 </span><span class="subxComment"># still take up 4 bytes so SubX can handle it</span>
<span id="L495" class="LineNr"> 495 </span> 00 00 00 00
<span id="L496" class="LineNr"> 496 </span><span class="subxComment"># 430:</span>
<span id="L497" class="LineNr"> 497 </span><span class="subxComment"># circular buffer: byte[16]</span>
<span id="L498" class="LineNr"> 498 </span> 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L499" class="LineNr"> 499 </span>
<span id="L500" class="LineNr"> 500 </span><span class="subxComment"># padding</span>
<span id="L501" class="LineNr"> 501 </span><span class="subxComment"># 440:</span>
<span id="L502" class="LineNr"> 502 </span>00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L503" class="LineNr"> 503 </span>00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L504" class="LineNr"> 504 </span>00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L505" class="LineNr"> 505 </span>00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L506" class="LineNr"> 506 </span>00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L507" class="LineNr"> 507 </span>00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L508" class="LineNr"> 508 </span>00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L509" class="LineNr"> 509 </span>00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L510" class="LineNr"> 510 </span>00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L511" class="LineNr"> 511 </span>00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L512" class="LineNr"> 512 </span>00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L513" class="LineNr"> 513 </span>00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
<span id="L514" class="LineNr"> 514 </span>
<span id="L515" class="LineNr"> 515 </span><span class="subxComment"># offset 500 (address 0x8100):</span>
<span id="L516" class="Folded"> 516 </span><span class="Folded">+-- 53 lines: # video mode info ---------------------------------------------------------------------------------------------------------------------------------------------------------</span>
<span id="L569" class="LineNr"> 569 </span>
<span id="L570" class="LineNr"> 570 </span><span class="subxComment"># offset 600 (address 0x8200):</span>
<span id="L571" class="Folded"> 571 </span><span class="Folded">+--161 lines: # interrupt descriptor table ----------------------------------------------------------------------------------------------------------------------------------------------</span>
<span id="L732" class="LineNr"> 732 </span>
<span id="L733" class="LineNr"> 733 </span><span class="subxComment">## the rest of this file has data</span>
<span id="L734" class="LineNr"> 734 </span>
<span id="L735" class="LineNr"> 735 </span><span class="subxComment"># offset a00 (address 0x8600):</span>
<span id="L736" class="Folded"> 736 </span><span class="Folded">+--152 lines: # translating keys to ASCII -----------------------------------------------------------------------------------------------------------------------------------------------</span>
<span id="L888" class="LineNr"> 888 </span>
<span id="L889" class="LineNr"> 889 </span><span class="subxComment"># offset 1000 (address 0x8c00)</span>
<span id="L890" class="Folded"> 890 </span><span class="Folded">+--236 lines: # Bitmaps for some ASCII characters (soon Unicode) ------------------------------------------------------------------------------------------------------------------------</span>
<span id="L1126" class="LineNr">1126 </span>
<span id="L1127" class="LineNr">1127 </span><span class="subxComment"># offset 1800 (address 0x9400)</span>
<span id="L1128" class="LineNr">1128 </span>
<span id="L1129" class="LineNr">1129 </span><span class="subxComment"># vim:ft=subx</span>
</pre>
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