Cisco Systems OL-26646-01 manual Resolving Insufficient 16-Bit I/O Space

Chapter 3 Maintaining the Server

Installing or Replacing Server Components

Resolving Insufficient 16-Bit I/O Space

The system has only 64 KB of legacy 16-bit I/O resources available. This 64 KB of I/O space is divided between the CPUs in the system because the PCIe controller is integrated into the CPUs. This server BIOS has the capability to dynamically detect the 16-bit I/O resource requirement for each CPU and then balance the 16-bit I/O resource allocation between the CPUs accordingly during the PCI bus enumeration phase of the BIOS POST.

When a large number of PCIe cards are installed in the system, the system BIOS might not have sufficient I/O space for some PCIe devices. If the system BIOS is not able to allocate the required I/O resources for any PCIe devices, the following symptoms have been observed:

•The system might get stuck in an infinite reset loop.

•The BIOS might appear to hang while initializing PCIe devices.

•The PCIe option ROMs might take excessive time to complete, which appears to lock up the system.

•PCIe boot devices might not be accessible from the BIOS.

•PCIe option ROMs might report initialization errors. These errors are seen before the BIOS passes control to the operating system.

•The keyboard might not work.

To work around this problem, rebalance the 16-bit I/O load using the following methods:

1.Physically remove any unused PCIe cards.

2.If the system has one or more Cisco virtual interface cards (VICs) installed, disable the PXE boot on the VICs that are not required for the system boot configuration by using the Network Adapters page in the Cisco IMC WebUI to free up some 16-bit I/O resources. Each VIC uses a minimum 16 KB of 16-bit I/O resource, so disabling PXE boot on Cisco VICs would free up some 16-bit I/O resources that can be used for other PCIe cards that are installed in the system.

	Cisco UCS C22 Server Installation and Service Guide
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