The KeyLargo custom IC, the third major component of the Xserve architecture, is connected to the main PCI bus through a dedicated PCI-to-PCI bridge. It provides all the I/O functions except Ethernet and FireWire. The KeyLargo IC provides two USB root hubs, a UATA interface, and support for the LED display.
DMA Support
Interrupt Support
USB Interface
Serial Interface
Ultra ATA Interface
Power Controller
System Monitor IC
System Activity Lights
Device Identification
The KeyLargo IC provides DB-DMA (descriptor-based direct memory access) support for the UATA interface and the LED matrix display. The DB DMA system provides a scatter-gather process based on memory-resident data structures that describe the data transfers. The DMA engine is enhanced to allow bursting of data files for improved performance.
The interrupt controller for the Xserve system is an MPIC cell in the KeyLargo IC. In addition to accepting all the KeyLargo internal interrupt sources, the MPIC controller accepts external interrupts from dedicated interrupt pins and serial interrupts from the U2 serial interrupt stream. The signals from the U2 IC are synchronized to the operation of the MPIC circuitry, so there is no additional interrupt latency on the U2 interrupts.
The KeyLargo IC implements two independent USB root hubs, each of which is connected to one of the ports on the back panel of the computer. The use of two independent hubs allows both USB ports to support high data rate devices at the same time with no degradation of their performance. If a user connects a high-speed device to one port and another high-speed device to the other, both devices can operate at their full data rates.
The two external USB connectors support USB devices with data transfer rates of 1.5 Mbps or 12 Mbps. For more information, see “USB Ports”.
The USB ports comply with the Universal Serial Bus Specification 1.1 Final Draft Revision. The USB register set complies with the Open Host Controller Interface (OHCI) specification.
The KeyLargo IC implements an RS-232-compatible serial port for use with a terminal. See see “Serial Port”. You can use the RI input on the serial port connector to wake the Xserve system from sleep mode.
In the slot load Xserve, the KeyLargo IC provides an ultra ATA (UATA) interface. The UATA interface supports the CD-ROM drive or optional Combo drive mounted on the front panel.
For information about the optical drive, see “CD-ROM Drive” or “Combo (DVD-ROM/CD-RW) Drive (Optional)”.
The KeyLargo IC provides DB-DMA (descriptor-based direct memory access) support for the UATA interface.
The power management controller in Xserve is a microcontroller called the PMU99. It supports several modes of power management that provide significantly lower power consumption than previous systems.
The Xserve hardware contains an IC that monitors system voltages and the operation of both fans in the Xserve enclosure. Voltages monitored include 5 V main, 12 V main, 3.3 V trickle, 2.5 V sleep, logic Vcore and processor Vcore. The system monitor IC also contains a built-in temperature sensor that measures the hardware’s ambient temperature to a resolution of 1 degree C; a second sensor on the processor card measures local processor temperature. Software can access the system monitor IC through the second U2 IIC bus at port address 0x5A.
Two rows of eight lights indicate system activity. In a server with a single processor, the rows of system activity lights operate together; in a dual-processor server, the rows of lights operate independently to show each processor’s activity. In that case, CPU 0 is shown by the top row, CPU 1 by the bottom.
Each Xserve boot ROM contains a unique device serial number. However, because the boot ROM is a flash EPROM device, it is possible to overwrite the serial number and lose it irrecoverably. As an alternative, software that needs to identify an individual Xserve computer can access the local-mac-address property of its Ethernet node, which is set by Open Firmware at boot time. You can read this property using a tool such as IORegistry Explorer.