Messages in this thread | | | Date | Fri, 26 Aug 2005 15:50:50 +0100 (BST) | From | "Maciej W. Rozycki" <> | Subject | Re: APIC version and 8-bit APIC IDs |
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On Fri, 26 Aug 2005, Martin Wilck wrote:
> Unless I am mistaken, the MP spec does not say that _CPUs_ must start from 0. > We had an IO-APIC at 0. The MP spec says that the IDs must be unique (I am > told this isn't true any more because an IO APIC and a CPU may have the same > ID) and _need not_ be consecutive.
You are unfortunately mistaken -- the spec is explicit about *local* APIC IDs having to start at 0. There are at least two places in the spec that refer to that.
> We tried different setups; one had IO APICs at 0,1,2 and CPUs starting at 16. > I can't see that this is forbidden (the reason is that the IO-APICs have only > 4-bit APIC ID registers). Anyway we changed it now to have both IO-APICs and > CPUs start at 0.
You can always assign 0, 16, 17, etc. to local APICs and then 1, 2, 3, etc. for I/O APICs. Frankly I don't know what the actual justification behind the requirement is. Note that the ID of 0 need not necessarily belong to the BSP.
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