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<a href='https://github.com/akkartik/mu/blob/main/102keyboard.subx'>https://github.com/akkartik/mu/blob/main/102keyboard.subx</a>
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<span id="L1" class="LineNr"> 1 </span><span class="subxComment"># check keyboard for a key</span>
<span id="L2" class="LineNr"> 2 </span><span class="subxComment"># return 0 on no keypress or unrecognized key</span>
<span id="L3" class="LineNr"> 3 </span><span class="subxComment">#</span>
<span id="L4" class="LineNr"> 4 </span><span class="subxComment"># We need to do this in machine code because Mu doesn't have global variables</span>
<span id="L5" class="LineNr"> 5 </span><span class="subxComment"># yet (for the keyboard buffer).</span>
<span id="L6" class="LineNr"> 6 </span>
<span id="L7" class="LineNr"> 7 </span>== code
<span id="L8" class="LineNr"> 8 </span>
<span id="L9" class="LineNr"> 9 </span><span class="subxComment"># Most keys correspond to their ASCII/Unicode values.</span>
<span id="L10" class="LineNr">10 </span><span class="subxComment"># TODO: Support for international keyboards and multi-byte Unicode.</span>
<span id="L11" class="LineNr">11 </span><span class="subxComment">#</span>
<span id="L12" class="LineNr">12 </span><span class="subxComment"># However there are some exceptions that have no assigned place in Unicode</span>
<span id="L13" class="LineNr">13 </span><span class="subxComment"># (and with good reason):</span>
<span id="L14" class="LineNr">14 </span><span class="subxComment"># 0x80 = left arrow ←</span>
<span id="L15" class="LineNr">15 </span><span class="subxComment"># 0x81 = down arrow ↓</span>
<span id="L16" class="LineNr">16 </span><span class="subxComment"># 0x82 = up arrow ↑</span>
<span id="L17" class="LineNr">17 </span><span class="subxComment"># 0x83 = right arrow →</span>
<span id="L18" class="LineNr">18 </span><span class="subxComment"># These code points are not used by Unicode and their semantics are agreed to</span>
<span id="L19" class="LineNr">19 </span><span class="subxComment"># be context-sensitive: <a href="https://en.wikipedia.org/wiki/C0_and_C1_control_codes#C1_controls.">https://en.wikipedia.org/wiki/C0_and_C1_control_codes#C1_controls.</a></span>
<span id="L20" class="LineNr">20 </span><span class="subxComment"># Mu cannibalizes them in yet another non-standard way.</span>
<span id="L21" class="LineNr">21 </span><span class="subxFunction">read-key</span>: <span class="subxComment"># kbd: (addr keyboard) -> result/eax: byte</span>
<span id="L22" class="LineNr">22 </span> <span class="subxS1Comment"># . prologue</span>
<span id="L23" class="LineNr">23 </span> 55/push-ebp
<span id="L24" class="LineNr">24 </span> 89/<- %ebp 4/r32/esp
<span id="L25" class="LineNr">25 </span> <span class="subxS1Comment"># . save registers</span>
<span id="L26" class="LineNr">26 </span> 51/push-ecx
<span id="L27" class="LineNr">27 </span> <span class="subxComment"># result = 0</span>
<span id="L28" class="LineNr">28 </span> b8/copy-to-eax 0/imm32
<span id="L29" class="LineNr">29 </span> <span class="subxComment"># ecx = keyboard</span>
<span id="L30" class="LineNr">30 </span> 8b/-> *(ebp+8) 1/r32/ecx
<span id="L31" class="LineNr">31 </span> 81 7/subop/compare %ecx 0/imm32
<span id="L32" class="LineNr">32 </span> {
<span id="L33" class="LineNr">33 </span> 75/jump-if-!= <span class="Constant">break</span>/disp8
<span id="L34" class="LineNr">34 </span> <span class="subxComment"># var buffer-byte-addr/ecx: (addr byte)</span>
<span id="L35" class="LineNr">35 </span> 8b/-> *<span class="SpecialChar">Keyboard-buffer</span>:read 1/r32/CL
<span id="L36" class="LineNr">36 </span> 81 0/subop/add %ecx <span class="SpecialChar">Keyboard-buffer</span>:data/imm32
<span id="L37" class="LineNr">37 </span> <span class="subxComment"># var next-key/eax: byte = *buffer-byte-addr</span>
<span id="L38" class="LineNr">38 </span> 8a/byte-> *ecx 0/r32/AL
<span id="L39" class="LineNr">39 </span> <span class="subxComment"># if (next-key != 0) lock and remove from keyboard buffer</span>
<span id="L40" class="LineNr">40 </span> 3d/compare-eax-with 0/imm32
<span id="L41" class="LineNr">41 </span> {
<span id="L42" class="LineNr">42 </span> 74/jump-if-= <span class="Constant">break</span>/disp8
<span id="L43" class="LineNr">43 </span> fa/disable-interrupts
<span id="L44" class="LineNr">44 </span> c6 0/subop/copy-byte *ecx 0/imm8
<span id="L45" class="LineNr">45 </span> ff 0/subop/increment *<span class="SpecialChar">Keyboard-buffer</span>:read
<span id="L46" class="LineNr">46 </span> 81 4/subop/and *<span class="SpecialChar">Keyboard-buffer</span>:read 0x0f/imm32
<span id="L47" class="LineNr">47 </span> fb/enable-interrupts
<span id="L48" class="LineNr">48 </span> }
<span id="L49" class="LineNr">49 </span> <span class="subxComment"># return</span>
<span id="L50" class="LineNr">50 </span> eb $read-key:end/disp8
<span id="L51" class="LineNr">51 </span> }
<span id="L52" class="LineNr">52 </span> <span class="subxComment"># TODO: fake keyboard</span>
<span id="L53" class="LineNr">53 </span><span class="Constant">$read-key:end</span>:
<span id="L54" class="LineNr">54 </span> <span class="subxS1Comment"># . restore registers</span>
<span id="L55" class="LineNr">55 </span> 59/pop-to-ecx
<span id="L56" class="LineNr">56 </span> <span class="subxS1Comment"># . epilogue</span>
<span id="L57" class="LineNr">57 </span> 89/<- %esp 5/r32/ebp
<span id="L58" class="LineNr">58 </span> 5d/pop-to-ebp
<span id="L59" class="LineNr">59 </span> c3/return
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