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<a name="Register-Names-21"></a>
<h4 class="subsubsection">9.55.2.2 Register Names</h4>
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<p>The assembly syntax for a register file entry is the “short” name for
a TIE register file followed by the index into that register file. For
example, the general-purpose <code>AR</code> register file has a short name of
<code>a</code>, so these registers are named <code>a0</code>…<code>a15</code>.
As a special feature, <code>sp</code> is also supported as a synonym for
<code>a1</code>. Additional registers may be added by processor configuration
options and by designer-defined TIE extensions. An initial ‘<samp>$</samp>’
character is optional in all register names.
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