XEN IV: CPU Complex
The CPU Complex on the XEN card is a standard PC. The choice of a PC architecture was based on several considerations:
A PC based CPU complex will be the cheapest to implement because of use of standard components
A PC based development system can be used easily for development. There is no need to cross compile to a different platform.
Many Real Time operating system choices are available for the PC platform
The OMC will be a Windows 2000 based Workstation using the same processor, so there will be byte swapping problems between the OMC and the XEN/CAS cards.
The CPU Complex will be equipped with 64 Mbytes of RAM, 8 Mbytes of ROM and a standard 10/100 Mbps Ethernet port for message communication between the XEN processor and the rest of the switch.
In addition to the standard PC functionality, the CPU Complex will support a watchdog monitor. The watchdog monitors main objective is to reset the processor if it finds that the hardware or software are hanging. This watchdog signal is passed to seven other XEN processors in the processor group. Thus the CPU complex also supports inputs from the watchdog signals of seven other XEN processors. A watchdog for another XEN processor will be reported to the CAS card. On self watchdog, the board will be reset.
The XEN card accepts power from a unregulated power supply and this module provides a regulated power supply interface to the card. A fringe benefit of a onboard power supply is that it simplifies software handling, as power supply failure don’t have to be delt with separately.
It may be noted that the Power Supply is mounted as a child card on the XEN card. This is required because typically Power Supply failure rates are much higher than other components. Thus when a Power Supply on a XEN card fails, it can be replaced onsite with a new Power Supply child card. Only the child card will have to be shipped for repair.