Abstract: The inventive system includes an I/O subsystem that controls the synchronization of an off-line CPU to an on-line CPU, such that much of the synchronization operation takes place essentially as a background task for the on-line CPU. The I/O subsystem requests that the on-line CPU provide certain register and memory state information to general purpose registers on an I/O board. The I/O subsystem then provides the register contents to general purpose registers on the off-line CPU board, and the off-line CPU uses the information to set the states of certain of its registers and memory. The I/O system further includes a DMA engine that, at a time set by the I/O subsystem, copies pages of memory from the on-line CPU to the off-line CPU. At the end of the synchronization operation, the off-line CPU is directed to write to a predetermined register on the I/O board. When the off-line CPU performs the write operation, it indicates that the off-line CPU is in a known state and ready to go on-line.

Abstract: A fault-tolerant maintenance bus architecture provides dual maintenance buses interconnecting each of a plurality of parent circuit boards. The two maintenance buses are each connected to a pair of system management modules (SMMs) that are configured to perform a variety of maintenance bus activities. Within each parent board are a pair of redundant bridges each having a unique address. One bridge is connected to the first maintenance bus while a second bridge is connected to the second maintenance bus of the pair. A child maintenance bus interconnects the two bridges one a child circuit board. The child maintenance bus is itself interconnected with a variety of monitor and control to functions on maintenance bus-compatible subsystem components. The SMMs can address components on each child board individually and receive appropriate responses therefrom. In the event of a bus failure, the other bus can still communicate with child subsystem components via the unaffected bridge.