title: What does the instruction mrc p15 do in ARM inline assembly?
body: <p>What does this line in ARM assembly do?</p>
  <pre><code>mrc p15, 0, %0, c9, c13, 0&quot; : : &quot;r&quot; (counter)
  </code></pre>
  <p>What is <code>p15</code>?  Usually registers are prefixed with <code>r</code> such as in <code>r15</code>.</p>
  <p>What is the symbol <code>::</code> and what are the roles or <code>c9, c1</code>?</p>