title: How SCI - System Control Interrupt vector is defined?
body: <p>According to the ACPI spec, The <strong>FADT</strong> (Fixed ACPI Description Table) table contains a field that reports the <strong>SCI interrupt</strong> number to OS. The field is defined as below:</p>
  
  <p><a href="https://i.stack.imgur.com/hN5OB.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/hN5OB.png" alt="enter image description here"></a></p>
  
  <p>I dumped the FADT table on an Intel x86 platform and see the SCI interrupt is associated with the number <code>9</code>:</p>
  
  <p><a href="https://i.stack.imgur.com/cGxsS.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/cGxsS.png" alt="enter image description here"></a></p>
  
  <p>But according to the Intel Manual, <code>0-31</code> are reserved vectors for IA architecturally defined interrupts. Specifically, the <code>9</code> is defined as:</p>
  
  <p><a href="https://i.stack.imgur.com/I8SRi.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/I8SRi.png" alt="enter image description here"></a></p>
  
  <p>So, according to the note, the <code>9</code> is not generated after I386 processor. So I guess that's why 9 can be <strong><em>salvaged</em></strong> for SCI. This can be seen as a <strong>x86-specific implementation</strong> of the ACPI spec.</p>
  
  <p>Am I right on this?</p>
  
  <h2>ADD 1</h2>
  
  <p>Seems I misunderstand something here. Will update later.</p>