消息（Messages）是PCIe中用于替代传统PCI边带信号（如中断、电源管理、错误上报）的核心机制。在这个章节spec定义了所有消息的公共头部格式、路由方式以及硬件处理规则。1、Message定义分组（13种）This document defines the following groups of Messages: INTx Interrupt Signaling, Power Management, Error Signaling, Locked Transaction Support, Slot Power Limit Support, Vendor-Defined Messages, Latency Tolerance Reporting (LTR), Optimized Buffer Flush/Fill (OBFF), Device Readiness Status (DRS), Function Readiness Status (FRS), Hierarchy ID Messages, Precision Time Measurement (PTM), Integrity and Data Encryption (IDE) Messages.