Intel 253668-032US Benutzerhandbuch

9-48   Vol. 3

PROCESSOR MANAGEMENT AND INITIALIZATION

9.11.7.1   Determining the Signature

An update that is successfully loaded into the processor provides a signature that 
matches the update revision of the currently functioning revision. This signature is 
available any time after the actual update has been loaded. Requesting the signature 
does not have a negative impact upon a loaded update.  
The procedure for determining this signature shown in Example 9-9.

Example 9-9.  Assembly Code to Retrieve the Update Revision

MOV

ECX, 08BH          ;IA32_BIOS_SIGN_ID

XOR

EAX, EAX           ;clear EAX

XOR

EDX, EDX           ;clear EDX

WRMSR                    ;Load 0 to MSR at 8BH

MOV

EAX, 1

cpuid

MOV

ECX, 08BH           ;IA32_BIOS_SIGN_ID

rdmsr                     ;Read Model Specific Register

 

If there is an update active in the processor, its revision is returned in the EDX 
register after the RDMSR instruction executes.

IA32_BIOS_SIGN_ID

Microcode Update Signature Register  

MSR Address:

08BH Accessed as a Qword

Default Value:

XXXX XXXX XXXX XXXXh

Access:

Read/Write 

The IA32_BIOS_SIGN_ID register is used to report the microcode update signature 
when CPUID executes. The signature is returned in the upper DWORD (Table 9-11).

9.11.7.2   Authenticating the Update

An update may be authenticated by the BIOS using the signature primitive, 
described above, and the algorithm in Example 9-10.

Table 9-11.  Microcode Update Signature 

Bit

Description

63:32

Microcode update signature. This field contains the signature of the currently loaded 

microcode update when read following the execution of the CPUID instruction, function 

1. It is required that this register field be pre-loaded with zero prior to executing the 

CPUID, function 1. If the field remains equal to zero, then there is no microcode update 

loaded. Another non-zero value will be the signature.

31:0

Reserved.