Bus master en信號
Type0的function：控制function發(fā)起Memory and I/O Read/Write Requests
- Bus Master Enable為0，不允許function發(fā)起Memory and I/O Read/Write Requests
- PF的Bus Master Enable 位于PF配置空間的Command Register的bit2，僅僅控制PF自身的請求，不會控制所屬VF的請求
- VF的Bus Master Enable，位于VF配置空間的Command Register的bit2，僅僅控制VF自身的請求
Type1的function：控制function向Upstream方向轉發(fā)Memory and I/O Read/Write Requests
- Switch upstream port的Bus Master Enable為0，
- 會將downstream side收到的Memory and I/O Read/Write Requests當做UR處理
- Switch upstream port自身不允許向upstream 方向發(fā)出Memory and I/O Read/Write Requests
參考文檔：PCI Express Base Specification, Rev. 5.0 Version 1.0
| Bus Master Enable - Controls the ability of a Function to issue Memory and I/O Read/Write Requests, and the ability of a Port to forward Memory and I/O Read/Write Requests in the Upstream direction ? Functions with a Type 0 Configuration Space Header: When this bit is Set, the Function is allowed to issue Memory or I/O Requests. When this bit is Clear, the Function is not allowed to issue any Memory or I/O Requests. Note that as MSI/MSI-X interrupt Messages are in-band memory writes, setting the Bus Master Enable bit to 0b disables MSI/MSI-X interrupt Messages as well. Requests other than Memory or I/O Requests are not controlled by this bit. Default value of this bit is 0b. This bit is hardwired to 0b if a Function does not generate Memory or I/O Requests. ? Functions with a Type 1 Configurations Space Header: This bit controls forwarding of Memory or I/O Requests by a Port in the Upstream direction. When this bit is 0b, Memory and I/O Requests received at a Root Port or the Downstream side of a Switch Port must be handled as Unsupported Requests (UR), and for Non-Posted Requests a Completion with UR Completion Status must be returned. This bit does not affect forwarding of Completions in either the Upstream or Downstream direction. The forwarding of Requests other than Memory or I/O Requests is not controlled by this bit. 文章來源：http://www.zghlxwxcb.cn/news/detail-431045.html Default value of this bit is 0b.文章來源地址http://www.zghlxwxcb.cn/news/detail-431045.html |
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