方案描述：

　　PCIe是新一代的总线接口。它采用了目前业内流行的点对点串行连接，比起PCI以及更早期的计算机总线的共享并行架构，每个设备都有自己的专用连接，不需要向整个总线请求带宽，而且可以把数据传输率提高到一个很高的频率。同时，在兼容性方面，PCIe在软件层面上兼容目前的PCI技术和设备，支持PCI设备和内存模组的初始化，也就是说目前的驱动程序、操作系统可无缝支持PCIe设备。 Xilinx 为FPGA的PCIe接入提供了一系列的方案。底层PCIe接口：在Virtex 5系列、Spartan 6系列、Virtex 6系列提供了PCIe的硬核，用户无需支付任何费用即可使用高速、高效的PCIe接口。对没有PCIe硬核的器件来说，Xilinx也提供了软核支持。

　　方案设计图：

　　xapp1052

　　Summary

　　This application note discusses how to design and implement a Bus Master design using Xilinx® Endpoint PCI Express® solutions. A performance demonstration reference design using Bus Mastering is included with this application note. The reference design can be used to gauge achievable performance in various systems and act as a starting point for an application-specific Bus Master Direct Memory Access (DMA). The reference design has been updated to add support for the Kintex®-7 family of FPGAs with updated source code using the Vivado® Design Suite targeting a Xilinx KC705 Evaluation Kit board.The reference desig also includes all files necessary to target the Integrated Blocks for PCI Express on the Virtex®-6 and Spartan®-6 FPGAs, the Endpoint Block Plus Wrapper Core for PCI Express using the Virtex-5 FPGA

　　Integrated Block for PCI Express, and the Endpoint PIPE for PCI Express targeting the Xilinx Spartan-3 family of devices. Also provided with the BMD hardware design is a kernel mode driver for both Windows and Linux along with both a Windows 32-bit and Linux software application. Source code is included for both Linux and Windows drivers and applications.

　　Note:The BMD hardware design, software drivers, and applications are provided as is with no implied

　　warranty or support.

　　Overview

　　The term Bus Master, used in the context of PCI Express, indicates the ability of a PCIe® port to initiate PCIe transactions, typically Memory Read and Write transactions. The most common application for Bus Mastering Endpoints is for DMA. DMA is a technique used for efficient transfer of data to and from host CPU system memory. DMA implementations have many advantages over standard programmed input/output (PIO) data transfers. PIO data transfers are executed directly by the CPU and are typically limited to one (or in some cases two) DWORDs at a time. For large data transfers, DMA implementations result in higher data

　　throughput because the DMA hardware engine is not limited to one or two DWORD transfers. In addition, the DMA engine offloads the CPU from directly transferring the data, resulting in better overall system performance through lower CPU utilization.

　　There are two basic types of DMA hardware implementations found in systems using PCI Express: System DMA implementation and Bus Master DMA (BMD) implementation.

　　System DMA implementations typically consist of a shared DMA engine that resides in a central location on the bus and can be used by any device that resides on the bus. System DMA

　　Xilinx是全球领先的可编程逻辑完整解决方案的供应商。Xilinx研发、制造并销售范围广泛的高级集成电路、软件设计工具以及作为预定义系统级功能的IP(Intellectual Property)核。

　　Xilinx(赛灵思)是全球领先的可编程逻辑完整解决方案的供应商。Xilinx研发、制造并销售范围广泛的高级集成电路、软件设计工具以及作为预定义系统级功能的IP(Intellectual Property)核。客户使用Xilinx及其合作伙伴的自动化软件工具和IP核对器件进行编程，从而完成特定的逻辑操作。Xilinx公司成立于 1984年，Xilinx首创了现场可编程逻辑阵列(FPGA)这一创新性的技术，并于1985年首次推出商业化产品。眼下Xilinx满足了全世界对 FPGA产品一半以上的需求。Xilinx产品线还包括复杂可编程逻辑器件(CPLD)。在某些控制应用方面CPLD通常比FPGA速度快，但其提供的逻辑资源较少。Xilinx可编程逻辑解决方案缩短了电子设备制造商开发产品的时间并加快了产品面市的速度，从而减小了制造商的风险。与采用传统方法如固定逻辑门阵列相比，利用Xilinx可编程器件，客户可以更快地设计和验证他们的电路。而且，由于Xilinx器件是只需要进行编程的标准部件，客户不需要象采用固定逻辑芯片时那样等待样品或者付出巨额成本。Xilinx产品已经被广泛应用于从无线电话基站到DVD播放机的数字电子应用技术中。传统的半导体公司只有几百个客户，而Xilinx在全世界有7，500多家客户及50，000多个设计开端。其客户包括Alcatel，Cisco Systems，EMC，Ericsson，Fujitsu，Hewlett-Packard，IBM，Lucent Technologies，Motorola，NEC，Nokia，Nortel，Samsung，Siemens，Sony，Oracle以及Toshiba。