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Chapter 3: Family Specific Considerations

1.The jitter of the source clock, to determine if it is appropriate for use as an input to a DCM.

2.The DCM configuration, to generate a 200 MHz clock on any appropriate DCM output (CLKFX, CLKDV, and so forth).

3.The jitter of the derived 200 MHz reference clock, to determine if it is appropriate for use as an input to an IDELAYCTRL.

For more information about the relevant timing parameters, see the Virtex-4 Datasheet and User Guide. As with the other implementation options, the derived 200 MHz reference clock must be distributed by a global clock buffer to the IDELAYCTRL instances.

Warning: The fixed frequency requirement of the source clock precludes the use of the PCI bus clock, unless the design is used in an embedded/closed system where the PCI bus clock is known to be a fixed frequency. See “Bus Clock Usage” for additional information about the allowed behavior of the PCI bus clock in compliant systems.

Regional Clock Usage

Some Virtex-4 implementations use a regional clock buffer (BUFR) for the PCI bus clock instead of a global clock buffer (BUFG). Use of a regional clock resource greatly improves the pin-to-pin clock to out of the interface while preserving full compliance. (Pin-to-pin clock to out is a silicon (chip) performance parameter important for PCI.)

Designers must be aware of additional constraints imposed by the use of regional clocks. Virtex-4 devices are divided into clock regions. Regional clock signals enter at the center of a given region, and span the region of entry in addition to the region above and the region below. The reach of a regional clock is physically limited to three clock regions. Figure 3-2illustrates BUFR driving three clock regions. See the Virtex-4 Datasheet and User Guide for more information about regional clocks.

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PCI v3.0.151 Getting Started Guide

 

 

UG157 August 31, 2005

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Xilinx PCI v3.0 manual Regional Clock Usage
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PCI v3.0 specifications

Xilinx PCI Express (PCIe) v3.0 technology represents a significant leap in performance and efficiency for high-speed data transfer applications. As a critical interface standard for connecting peripheral devices to a host system, PCIe v3.0 introduces numerous enhancements that ensure faster data rates, increased bandwidth, and lower latency, meeting the rigorous demands of modern computing environments.

One of the standout features of PCIe v3.0 is its increased data transfer rate, which doubles the bandwidth compared to its predecessor, PCIe v2.0. This version supports a maximum theoretical bandwidth of 8 GT/s (gigatransfers per second) per lane, leading to an aggregate bandwidth of up to 32 GB/s with four lanes operating simultaneously, which is crucial for applications in data-intensive fields such as telecommunications, data centers, and high-performance computing.

Xilinx’s PCIe v3.0 solutions incorporate advanced error-handling mechanisms and improved power management. The technology employs a robust 128/130b encoding scheme that minimizes overhead while ensuring data integrity. Additionally, PCIe v3.0 supports native high-speed signaling, which not only reduces power consumption but also enhances signal quality, leading to greater reliability in data transmission.

The flexibility of Xilinx’s PCIe v3.0 implementation makes it ideal for various applications, including artificial intelligence, machine learning, and video processing, where rapid data throughput is paramount. Moreover, Xilinx provides extensive support through its Vivado Design Suite, enabling developers to easily integrate PCIe functionality into their designs while optimizing performance for specific applications through customizable settings.

Another key characteristic is the backward compatibility with earlier PCIe versions. This ensures that existing hardware can leverage new capabilities without necessitating a complete overhaul of the infrastructure, enhancing investment protection for users. The inclusion of additional features such as enhanced message signaling and the ability to support up to 64 thousand in-flight transactions further boosts the efficiency of data handling in a multi-threaded environment.

In summary, Xilinx PCI Express v3.0 technology is a powerful solution that combines high bandwidth, reduced latency, and enhanced reliability, making it an essential component for advanced computing architectures. Its robust features, coupled with Xilinx’s design tools and support, provide developers with the resources needed to push the boundaries of data transfer capabilities in a growing range of applications.
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