The root complex is responsible for system configuration and enumeration of PCIe resources, and manages interrupts and errors for the PCIe tree. To further support simplicity and legacy constructs, a root complex and its endpoints share a single address space and communicate through memory reads and writes and interrupts. Internally, PCIe devices implement virtual PCI-to-PCI bridges and buses and logical structures that mimic the physical bridging and bus functions in legacy PCI-based systems as well as allow for support of the legacy protocols' interrupts and messages.
The Figure 1 exploded view shows logical details of virtual bridge and bus hierarchies in a PCIe implementation. Replicating logical PCI-based structures within PCIe devices eased the hardware and software migration between standards but left the new standard with limited extensibility, particularly to multiroot applications. The protocol remained focused on efficient interconnect for single root constructs - with a one-to-one relationship between a root and an endpoint.
To enable PCIe as the primary system interconnect for multiroot systems, the challenge is to work within or extend the standard specification to enable system architects to leverage the efficiency, scal-ability, and low-power advantages of PCIe and capitalize on its rich and rapidly growing and commoditizing ecosystem of processors and peripherals.
The solution to providing multiroot sup-port and enabling efficient system resource utilization and sharing within the PCIe specification may be much "simpler" than previously offered solutions. Revisiting the classical definition of emergence, a new approach suggests that the problems can be addressed within the current standard and ecosystem by focusing on the most basic PCIe elements, keeping the transactions simple, and rendering small switching solutions that, through multiplicity, combine to solve larger system switching problems.
Leveraging the constituent logical elements of a PCIe switch - the virtual PCI-to-PCI bridges and virtual PCI bus - the multiroot partitionable switch architecture creates multiple logical switches or switch partitions within a single switching device by using physical controls Figure 2.
Each independent partition represents a PCIe hierarchy whose configuration, switching operation, and reset logic are isolated from other partitions. Replication of the control and management structures associated with the virtual PCIe bus makes it possible to support multiple separate virtual PCI buses.
This approach allows multiple distinct root complexes to coexist on a PCIe-compliant switch. The ability to freely associate virtual PCI-to-PCI bridges to any of the established virtual buses adds more architectural flexibility. Association can take place either statically at the time of a fundamental reset to the switch or dynamically while the switch is operating.
The multiroot partitionable switch architecture then allows system designers to partition an n-port physical switch into n-partitions that is, 16 partitions for a port switch and the flexibility to assign any switch ports to any of the partitions as well as the unique capability to change the system configuration and port assignments dynamically during switch operation.
Further, within a given partition, any port can be assigned as the upstream or root port with the ability to move that root port as well during switch operation. Despite the independence of the partitions, the shared control logic for the partitions within the switch remains a global resource that can be controlled via the physical switches' System Management Bus SMBus or in band from any of the roots attached to any of the logical partitions.
This extends the flexibility of the architecture to allow the dynamic reallocation of resources to be initiated by roots within or outside a given partition. The switch architecture supports multiroot system architectures, enables advanced applications of the functionality that increase system configurability, and optimizes system resource utilization, availability, and security.
The most direct application of the architecture to aid system configurability is to replace multiple discrete physical PCIe switches with a single partitioned switch. Such a replacement shrinks the total cost of ownership by reducing power consumption, decreasing board space requirements, and lowering system interconnect costs.
In one paradigm, a multiroot system with a fixed set of computing resources leverages the partitionable switch architecture to enable a wide array of systems through the ability to efficiently map the compute resources to a varying number and an assortment of peripheral devices or cards.
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Version 1. At the same time, the transfer rate has incrementally risen from 2. Along with performance improvements, each version has introduced new features and increased energy efficiency. With a lofty standard of doubling bandwidth every few years to avoid becoming the bottleneck as processor speed and memory continues to increase rapidly, each revision presents new challenges for designers.
Potential for crosstalk and electrical discontinuity increases along with bandwidth, so new materials and design innovations continue to push the envelope.
The size of any PCI Express card, as well as the number of pins, is dictated by the number of lanes and total connections. The same holds true for all PCIe versions. Available PCIe sizes and their corresponding pin counts are as follows. This means an x1 expansion card can be installed in an x1, x4, x8 or x16 slot. The same applies in reverse, meaning you can install an x16 card into an x4 slot, for example, but only if the slot is the type configured with its rear side open.
In this case, however, the bandwidth would be limited to that of an x4 card. While the original PCIe 1.
As the bandwidth increases, so does the potential for crosstalk and discontinuity, making recent innovations in PCB trace materials and lane margining a prerequisite for this rapid evolution.
The technical versatility of the PCIe format is another important factor, and the focus on interchangeability has influenced the designers of PCIe test equipment and hardware in equal measure. Backwards compatibility between PCIe revisions has remained a hallmark, and slot sizes of 1x through 16x are congruous with any size PCIe card, with the smaller of the two items dictating the bandwidth availability.
Although the NVMe-oF specification is inherently similar to the NVMe base specification, characterizing the transport mechanisms adds additional complexity. The adoption of PCIe 4. Traffic flow monitoring, data storage and error detection functions require a higher performance standard from PCI Express tools, and this trend has continued unabated with PCIe 5.
The release of PCIe 5. To complement the 2X speed increase, electrical design emphasis was placed on signal integrity and equalization. These tools have been designed to accurately measure performance, rapidly detect issues and simulate use conditions for robust and comprehensive analysis.
Analyzers with detailed visibility into traffic flow and link performance enable comprehensive verification of the PCIe 5. Jamming tools with the capability to manipulate live traffic create a robust level of simulation that otherwise would not be possible.
The software behind these cutting-edge PCIe tools continues to tie it all together, with ever-improving interface and reporting enhancements that seamlessly unite the operator with the PCIe test case.
The group was formed in and now has over member companies developing products based on PCI-SIG released specifications. These specifications are free to their member organizations or individuals. Channel topologies have become much more complex as the data rates have increased.
Using simulation to optimize power and signal integrity is a recommended practice for PCIe link evaluation. Determining whether data packets are reliably transferred can be performed by utilizing protocol validation at the physical layer. A wide array of PCIe test tools are now available. With each successive generation, PCI Express test equipment has evolved to meet the increasingly stringent demands, enabling new and exciting solutions.
Feature-rich tools from industry-leading PCIe test equipment suppliers are ideally mobile and rugged, with readily-available training and certification. Given the backwards-compatible nature of the PCIe interface, interoperability for multiple sizes and versions and rapid upgradability are other overall characteristics of outstanding PCIe test equipment. A jammer can manipulate live traffic to simulate errors in real time. For PCIe testing, a jammer is an inline error injection tool that can simulate real-world conditions and shorten test cycles.
Often using pre-defined automated test scripts, a jammer can recreate a wide variety of error-testing scenarios. Jammers such as the Xgig are highly intelligent and protocol aware, and can utilize conditional jamming to maintain control over the test process and ensure comprehensive test coverage. Working in conjunction with a protocol analyzer or other PCIe tester, the jammer produces discernable triggers at the error injection points. By introducing errors into real-world environments, the responsiveness and efficacy of the error recovery process can be accurately discerned.
The protocol analyzer is a versatile PCI Express product tool for bus throughput and link performance measurement as well as packet monitoring and recording. Additional triggering, error reporting and filtering features can enable rapid error identification.
Jamming capabilities can artificially create latencies and retransmissions to exercise error-detection capabilities.
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