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新建文件 Hardware/Bus/PCI/PCIe_中的_Capability_结构的寻址.md

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# [PCIe 中的 Capability 结构的寻址](http://www.cnblogs.com/zhongzhe/p/3900111.html)
PCI-X 和PCIe 总线规范要求其设备必须支持 Capabilities 结构。在PCI 总线的基本配置空间中，包含一个 Capabilities Pointer 寄存器，该寄存器存放 Capabilities 结构链表的头指针。在一个PCIe 设备中，可能含有多个 Capability 结构，这些寄存器组成一个链表，如下图所示。
![PCIe 总线 Capability 结构的组成](imgs/PCIe_中的_Capability_结构的寻址/01.jpg)
其中每一个 Capability 结构都有唯一的 ID 号，每一个 Capability 寄存器都有一个指针，这个指针指向下一个 Capability 结构，从而组成一个单向链表结构，这个链表的最后一个 Capability 结构的指针为 0。链表开始的指针地址为 0x34 处的 1byte 数值，寻址过程如下。
![PCIe Config 空间 Capability 指针](imgs/PCIe_中的_Capability_结构的寻址/02.jpg)
1. We look at address 34h and see the address of the next capability register set (50h).
![查找 Capability 寄存器](imgs/PCIe_中的_Capability_结构的寻址/03.jpg)
2. We jump to 50h and see a capability ID of 05h (MSI Capability Structure). We look at the next capability pointer in 51h to find which address to jump to next (78h).
![查找 Capability 寄存器](imgs/PCIe_中的_Capability_结构的寻址/04.jpg)
3. We jump to 78h and see a capability ID of 01h (Power Management Capability Structure). We look at the next capability pointer in 79h to find which address to jump to the next (80h).
![查找 Capability 寄存器](imgs/PCIe_中的_Capability_结构的寻址/05.jpg)
4. We jump to 80h and see a capability ID of 10h (PCI Express Capability Structure). We see 00h as the next capability pointer in 81h signifying the end of the linked list.
![查找 Capability 寄存器](imgs/PCIe_中的_Capability_结构的寻址/06.jpg)