Appendix A Need More Pcie Slots; Multiple Pcie Expansion System Configurations - Magma EB7-X8G2 User Manual

Appendix A Need More PCIe Slots?

Multiple PCIe Expansion System Configurations

The PCI Express Local Bus Specification defines the bus as hierarchical, where logical PCI to PCI Bridges (PPBs) may be
used to add "levels" to the PCI bus hierarchy within a PCIe switch. Because hierarchies are organized systems arranged
into different levels, you can take advantage of this automatic organizing and layering to expand the number of
available PCIe slots beyond the number available in your computer's motherboard.
You can easily add two or more Magma expansion systems to your current system in a "fan-out" configuration. Each of
these configurations has advantages and uses. To determine which type of configuration you wish to use, you should first
understand a few basic facts:
1. In a desktop computer, the BIOS enumerates automatically behind logical PCI bridges. In the Magma
configuration, the BIOS looks beyond the Host card to find any PCIe cards installed in the expansion chassis
behind a PCIe switch. The PCIe switch, in turn, emulates logical PRBs. The BIOS can then configure the cards
and allocate resources. Empty PCIe slots are ignored during configuration.
In theory, your computer "should" be able to travel across up to 255 PCIe buses to identify
and configure all installed PCIe cards. The 255 PCI bus limit is actually a theoretical maximum.
The practical limit is somewhat lower and differs from one system to another, but should still be
a fairly large number.
In a desktop computer the bus numbers tend to be lower (0, 1, 2, etc.). Once the BIOS is
finished configuring everything and assigning resources, the Operating System starts loading
and activates the PCIe cards found.
When adding more Expansion Systems to an existing system, be sure to connect and test
them "one-at-a-time." This will allow you to quickly resolve any connectivity, or other, issues
right at the start. DO NOT INSTALL any 3rd Party PCIe cards into any system until ALL attached
systems are working correctly.
2. Most computers allow multiple logical bridges (and thus PCIe buses) to be correctly configured. Some
computers, unfortunately, place an arbitrary limit on the number of bridge levels that can be traveled during
power-on configuration. Your computer "power-on-software" should be compliant with the PCIe bus
specification in order to effectively use a Magma PCIe Expansion System. For a "fan-out" system configuration,
where more than one PCIe expansion system is being used, you should count all of the logical bridge levels to
your most deeply nested PCI bus to determine the maximum number of bridge levels that must be traveled.
Exceeding this number may cause software configuration conflicts even though hardware-wise the PCIe
system is properly configured.
3. For easier understanding, a given PCI system should be viewed as a "Resource Toll road" that runs from the
computer CPU (resource home), through the "Toll Booths" (the PCIe switches and logical PCI bridges), to the
"Resource Users" (PCIe Cards). As in the case of a real Toll Road, the more Toll Booths you have to cross (even if
it takes a nanosecond), the longer it will take you (your data) to get from the PCIe Card to the CPU and back
again. Under most circumstances the effect cannot even be detected. However, under other conditions, it
can be important to know about.
EB7-X8G2 | Appendix A Need More PCIe Slots?
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