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Date: July 25, 2000
Technical Note: TN13 revision 3
CPG Technical Marketing

AMD DuronTM Processor Rev. A0: CPUID Reporting of L2 Cache Size
Abstract: The AMD DuronTM processor, revision A0 (CPUID 630) contains
an erratum that will result in the incorrect reporting of the
internal L2 cache size if the CPUID extended function
8000_0006h is used. If BIOS or any other utility uses this
instruction when reporting the L2 cache size, then it is
recommended that BIOS or the utility adjust the return value
from this instruction as described below in "Solution." For
more information, refer to the:
I AMD DuronTM Processor Revision Guide, order# 23865
I AMD Processor Recognition Application Note, order# 20734
I AMD AthlonTM and AMD DuronTM Processors Recognition
Addendum, order# 21922.

Description: When the CPUID extended function 8000_0006h is used to
obtain cache information, the AMD Duron processor rev. A0
(CPUID 630) reports the L2 cache size incorrectly.

Solution: Consider the code below for executing CPUID extended
function 8000_0006h:
mov eax, 80000006h ;CPUID Fn 80000006h
CPUID ;ecx[31:16] = L2 size info
shr ecx, 16 ;cx = L2 size (in either KB or 64KB)

Do not use CPUID to determine the L2 cache size for the
AMD Duron processor. Instead use the following code:
; Check for A0 revision Duron(tm) processor
mov eax, 1 ;CPUID Fn 1
CPUID ;ax = CPU version information
cmp ax, 0630h ;Is CPU a Rev A0 AMD Duron processor?
mov cx, 64 ;(assume yes)
je @f ; YES--L2 size is 64K
; NO---use CPUID function to get
; L2 size
mov eax, 80000006h ;CPUID Fn 80000006h
CPUID ;ecx[31:16] = L2 size info
shr ecx, 16 ;Shift L2 size bits into cx

@@:;cx = L2 size in KB

Trademarks--AMD, the AMD logo, AMD Athlon, AMD Duron, and combinations thereof, are trademarks of Advanced Micro Devices, Inc.