Understanding Microcode Updates for Intel® Xeon® Processors

Microcode Definition:

Microcode is a low-level code that defines the processor's instruction set and behavior. It can be updated to fix bugs, improve performance, and add new features.

Importance:

Each unique processor stepping/package combination has an associated microcode update. A processor without the correct microcode update is considered to be operating out of spec.

BIOS/UEFI Responsibility:

• The BIOS (Basic Input/Output System) or UEFI (Unified Extensible Firmware Interface) ensures all logical processors in the system have the correct microcode update installed as soon as they wake up.
• During the Power-On Self-Test (POST), the BIOS loads the microcode update into the processor, ensuring it operates correctly and efficiently.

Microcode Storage:

• Microcode updates are stored in non-volatile flash memory, which retains data even when the power is turned off.
• During early POST, the BIOS checks the processor signature (a unique identifier for the processor) and uses it to look up the appropriate microcode update from the stored updates.

Loading Microcode:

• A revision check should be performed before loading a microcode update for performance considerations into the BIOS, ensuring only newer revisions are loaded.
• Loading a debug microcode update requires the debug capability to be enabled via a hardware mechanism (such as a jumper) or the IA32_DEBUG_INTERFACE Model-Specific Register (MSR).

Intel Platform Updates:

• Intel regularly provides microcode updates through platform updates, which can be found in the Intel IPU (Intel Platform Update) Update Guidance document.
• Microcode patches can be obtained from repositories such as GitHub. 

Contact for Updates:

• For the latest microcode updates, contact your Intel Field Representative for the most recent updates and guidance specific to your processor and system configuration.

Verification and Debugging:

Revision Check:

• Perform a revision check before loading a microcode update to ensure only newer revisions are loaded, maintaining optimal performance and stability.

Debug Microcode Updates:

• Loading a debug microcode update requires enabling the debug capability via a hardware mechanism or the IA32_DEBUG_INTERFACE MSR, typically used for development and troubleshooting purposes.

Summary:

Updating microcode involves several critical steps:

• Ensuring the BIOS loads the correct microcode during POST. 
• Storing updates in non-volatile memory.
• Performing revision checks to load only newer updates.
• Utilizing utilities and repositories for specific platforms.
• Contacting Intel representatives for the latest updates.

Properly applied microcode updates ensure the processor operates within specification and benefits from the latest enhancements, fixes, and performance improvements.

For further details, reach out to your board manufacturer or your Intel representative for the most recent updates.