Re: APIC version and 8-bit APIC IDs

[Maciej W. Rozycki]

On Wed, 31 Aug 2005, Martin Wilck wrote:

> We are wondering why these masks are there in the subarch code at all. After
> all, whether or not 8-bit APIC IDs are supported depends mainly on the CPU
> type used. Why wouldn't it possible to have a "default" architecture with APIC
> IDs > 15, if the CPUs allow it?

 It actually depends on the APIC type, rather than the CPU.  E.g. with 
Pentium systems the width of the ID is either 4 bits or 8 bits, depending 
on whether the integrated or an external 82489DX APIC is used.  This 
should be able to be determined by the APIC version; for v <= 0xf the ID 
is 8-bit and for v >= 0x10 it used to be 4-bit.  Now you only need to 
determine what is the value of v above 0x10 that makes the ID 8-bit again.

  Maciej
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