ACPI SPEC 的 OSPM/ACPI Global System 這張圖描述了 ACPI/OSPM 裡軟體與硬體元件的關係，應用程式需透過 OS Kernal 與系統電源管理 (OSPM) 溝通、與裝置驅動溝通、與ACPI 驅動溝通，裝置驅動可控制底層硬體，而ACPI 驅動 (ACPI.sys) 可透過 BIOS 的 ACPI 資訊 (包括 ACPI 暫存器組、ACPI 靜態表、ACPI 韌體) 與底層硬體溝通。所以 ACPI 不是單純的軟體或韌體或硬體，而是一個完整的介面規格，橫跨軟體、韌體、硬體。
這邊先提一下名詞後續會較好表達
| 縮寫 | 全名 |
|---|---|
| RSDP | Root System Description Pointer |
| RSDT | Root System Description Table |
| XSDT | Extended System Description Table |
SPEC 的 Root System Description Pointer and Table中，簡易說明了ACPI Table的尋找過程，Root代表最上層，所以ACPI 由 RSDP 的 Signature “RSD PTR” 開始，結構內包含了兩個位址，其中之一對應的位址，Signature 為 XSDT，XSDT Table結構又包含了許多 ACPI Table 的 Entry Address，每個 Address 的 Table 都有各自的 Signature 與各自的 Structure。
找 ACPI 最重要的就是如何尋找 RSDP，BIOS 開機過程會將 ROM 裡的 ACPI Data複製到 Memory 中，SPEC 中提到會在 1M 以下的空間中，通常是在0x000E0000 到 0x000FFFFF 之間，並使用特定的 Signature “RSD PTR”，找到 RSD PTR 就能以對應的 RSDP 結構解析資料，如搜尋不到就暴力搜尋 00000000h 到 FFFFFFFFh。RSDP中最重要的兩個資訊就是32bit 的RSDT Address 與 64bit 的 XSDT Address，兩者差異只在 BIT 位元數的不同，內容是一樣的。
RSDP Structure
| Field | Byte Length | Byte Offset | Description |
|---|---|---|---|
| Signature | 8 | 0 | "RSD PTR" (Notice that this signature must contain a trailing blank character.) |
| Checksum | 1 | 8 | This is the checksum of the fields defined in the ACPI 1.0 specification. This includes only the first 20 bytes of this table, bytes 0 to 19, including the checksum field. These bytes must sum to zero. |
| OEMID | 6 | 9 | An OEM-supplied string that identifies the OEM. |
| Revision | 1 | 15 | The revision of this structure. Larger revision numbers are backward compatible to lower revision numbers. The ACPI version 1.0 revision number of this table is zero. The ACPI version 1.0 RSDP Structure only includes the first 20 bytes of this table, bytes 0 to 19. It does not include the Length field and beyond. The current value for this field is 2. |
| RsdtAddress | 4 | 16 | 32 bit physical address of the RSDT table. |
| Length | 4 | 20 | The length of the table, in bytes, including the header, starting from offset 0. This field is used to record the size of the entire table. This field is not available in the ACPI version 1.0 RSDP Structure. |
| XsdtAddress | 8 | 24 | 64 bit physical address of the XSDT table. |
| Extended Checksum | 1 | 32 | This is a checksum of the entire table, including both checksum fields. |
| Reserved | 3 | 33 | Reserved field |
RSDT Structure
| Field | Byte Length | Byte Offset | Description |
|---|---|---|---|
| Signature | 4 | 0 | "RSDT" Signature for the Root System Description Table. |
| Length | 4 | 4 | Length, in bytes, of the entire RSDT. The length implies the number of Entry fields (n) at the end of the table. |
| Revision | 1 | 8 | 1 |
| Checksum | 1 | 9 | Entire table must sum to zero. |
| OEMID | 6 | 10 | OEM ID |
| OEM Table ID | 8 | 16 | For the RSDT, the table ID is the manufacture model ID. This field must match the OEM Table ID in the FADT. |
| OEM Revision | 4 | 24 | OEM revision of RSDT table for supplied OEM Table ID. |
| Creator ID | 4 | 28 | Vendor ID of utility that created the table. For tables containing Definition Blocks, this is the ID for the ASL Compiler. |
| Creator Revision | 4 | 32 | Revision of utility that created the table. For tables containing Definition Blocks, this is the revision for the ASL Compiler. |
| Entry | 4*n | 36 | An array of 32-bit physical addresses that point to other DESCRIPTION_HEADERs. OSPM assumes at least the DESCRIPTION_HEADER is addressable, and then can further address the table based upon its Length field. |
XSDT Structure
| Field | Byte Length | Byte Offset | Description |
|---|---|---|---|
| Signature | 4 | 0 | "XSDT". Signature for the Extended System Description Table. |
| Length | 4 | 4 | Length, in bytes, of the entire table. The length implies the number of Entry fields (n) at the end of the table. |
| Revision | 1 | 8 | 1 |
| Checksum | 1 | 9 | Entire table must sum to zero. |
| OEMID | 6 | 10 | OEM ID |
| OEM Table ID | 8 | 16 | For the XSDT, the table ID is the manufacture model ID. This field must match the OEM Table ID in the FADT. |
| OEM Revision | 4 | 24 | OEM revision of XSDT table for supplied OEM Table ID. |
| Creator ID | 4 | 28 | Vendor ID of utility that created the table. For tables containing Definition Blocks, this is the ID for the ASL Compiler. |
| Creator Revision | 4 | 32 | Revision of utility that created the table. For tables containing Definition Blocks, this is the revision for the ASL Compiler. |
| Entry | 8*n | 36 | An array of 64-bit physical addresses that point to other DESCRIPTION_HEADERs. OSPM assumes at least the DESCRIPTION_HEADER is addressable, and then can further address the table based upon its Length field. |
RSDT 與 XSDT Structure 裡包含的許多 Entry，對應的 Signature 都有其獨特的涵義，簡略代表了Entry Table 裡的資料內容，詳細參考下列表格。
Signatures for tables defined by ACPI
| Signature | Description |
|---|---|
| APIC | Multiple APIC Description Table |
| BERT | Boot Error Record Table |
| BGRT | Boot Graphics Resource Table |
| CCEL | Virtual Firmware Confidential Computing Event Log Table. |
| CPEP | Corrected Platform Error Polling Table |
| DSDT | Differentiated System Description Table |
| ECDT | Embedded Controller Boot Resources Table |
| EINJ | Error Injection Table |
| ERST | Error Record Serialization Table |
| FACP | Fixed ACPI Description Table (FADT) |
| FACS | Firmware ACPI Control Structure |
| FPDT | Firmware Performance Data Table |
| GTDT | Generic Timer Description Table |
| HEST | Hardware Error Source Table |
| MISC | Miscellaneous GUIDed Table Entries |
| MSCT | Maximum System Characteristics Table |
| MPST | Memory Power StateTable |
| NFIT | NVDIMM Firmware Interface Table |
| OEMx | OEM Specific Information Tables |
| PCCT | Platform Communications Channel Table |
| PHAT | Platform Health Assessment Table |
| PMTT | Platform Memory Topology Table |
| PPTT | Processor Properties Topology Table |
| PSDT | Persistent System Description Table |
| RASF | ACPI RAS Feature Table |
| RAS2 | ACPI RAS2 Feature Table |
| RSDT | Root System Description Table |
| SBST | Smart Battery Specification Table |
| SDEV | Secure DEVices Table |
| SLIT | System Locality Distance Information Table |
| SRAT | System Resource Affinity Table |
| SSDT | Secondary System Description Table |
| SVKL | Storage Volume Key Data table in the Intel Trusted Domain Extensions. |
| XSDT | Extended System Description Table |
Signatures for tables reserved by ACPI 這部分將 ACPI 保留的特定 Signature做整理。
| Signature | Description |
|---|---|
| AEST | Arm Error Source Table. |
| AGDI | Arm Generic Diagnostic Dump and Reset Interface. |
| APMT | Arm Performance Monitoring Unit table. |
| BDAT | BIOS Data ACPI Table – exposing platform margining data. |
| BOOT | Reserved Signature |
| CEDT | CXL Early Discovery Table. |
| CSRT | Core System Resource Table. |
| DBGP | Debug Port Table. |
| DBG2 | Debug Port Table 2. |
| DMAR | DMA Remapping Table. |
| DRTM | Dynamic Root of Trust for Measurement Table. |
| DTPR | DMA TXT Protected Range. |
| ETDT | Event Timer Description Table (Obsolete). IA-PC Multimedia Timers Specification. This signature has been superseded by “HPET” (below) and is now obsolete. |
| HPET | IA-PC High Precision Event Timer Table. |
| IBFT | iSCSI Boot Firmware Table. |
| IERS | Inline Encryption Reporting Structure. |
| IORT | I/O Remapping Table. |
| IVRS | I/O Virtualization Reporting Structure. |
| KEYP | Key Programming Interface for Root Complex Integrity and Data Encryption (IDE). |
| LPIT | Low Power Idle Table. |
| MCFG | PCI Express Memory-mapped Configuration Space base address description table. PCI Firmware Specification, Revision 3.0. |
| MCHI | Management Controller Host Interface table. DSP0256 Management Component Transport Protocol (MCTP) Host Interface Specification. |
| MHSP | Microsoft Pluton Security Processor Table. |
| MPAM | Arm Memory Partitioning And Monitoring. |
| MSDM | Microsoft Data Management Table. |
| NBFT | NVMe-over-Fabric (NVMe-oF) Boot Firmware Table. |
| PRMT | Platform Runtime Mechanism Table. |
| RGRT | Regulatory Graphics Resource Table. |
| SDEI | Software Delegated Exceptions Interface. |
| SLIC | Microsoft Software Licensing table. |
| SPCR | Microsoft Serial Port Console Redirection table. |
| SPMI | Server Platform Management Interface table. |
| STAO | _STA Override table. |
| SWFT | Sound Wire File Table table. |
| TCPA | Trusted Computing Platform Alliance Capabilities Table. TCPA PC Specific Implementation Specification. |
| TPM2 | Trusted Platform Module 2 Table. |
| UEFI | Unified Extensible Firmware Interface Specification. |
| WAET | Windows ACPI Emulated Devices Table. |
| WDAT | Watch Dog Action Table. Requirements for Hardware Watchdog Timers Supported by Windows - Design Specification. |
| WDDT | Watchdog Descriptor Table. The table passes Watchdog-related information to the OS. |
| WDRT | Watchdog Resource Table. Watchdog Timer Hardware Requirements for Windows Server 2003. |
| WPBT | Windows Platform Binary Table. |
| WSMT | Windows Security Mitigations Table. |
| XENV | Xen Project. |
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