# CpuPei
**Index**: 0074 | **Size**: 61 KB (source) | **Arch**: x64 | **Phase**: PEI

## Overview
CpuPei is a PEI driver responsible for early CPU initialization on Intel Purley platforms. It programs MTRRs (Memory Type Range Registers), processes BIST (Built-In Self Test) data for each CPU thread, publishes CPU-related HOBs, and handles cache control initialization before memory is fully available.

## Key Functions
- MTRR programming for cache control (EarlyInitMtrr, ProgramMtrrs)
- BIST (Built-In Self Test) data collection and HOB publication
- CPU feature detection via CPUID
- Processor number and cache info HOB generation
- BIOS debug lock configuration
- Microcode patch level reporting
- CPU frequency ratio detection

## Protocols / PPIs / Dependencies
- PEI CPU PPI
- PeiServicesTablePointer PPI
- EFI_PEI_PPI_DESCRIPTOR

## Platform
HR650X (Purley platform, Skylake-SP / Xeon Scalable)