HyperTransport's third time around adds more robust performance and features to an already successful run. The new standard not only extends HyperTransport's range and throughput, it also moves it into high-reliability environments that require features such as hot-swapping and power management.
Not surprisingly, HyperTranport 3.0 raises the link speed with a top end of 2.6 GHz. It remains backward-compatible with the 1.0 and 2.0 standard devices. Version 2.0 introduced doubledata-rate transfers, so the latest 3.0 high point is 20 Gbytes/s per link.
Auto negotiation handles differences between devices. This becomes more important with the addition of features like hot-swapping and the power-management mode, since device operation and connectivity can change over time.
Hot-swap support is key to Hyper-Transport's success in many applications, including its latest foray into mezzanine cards and potential new standardsin areas like MicroTCA. With it, high-performance processors and devices can be added to and removed from a system as necessary.
The AC mode extends HyperTransport across the backplane. Its new signaling convention slows down the overall transfer rate by a small amount while permitting much longer distances. It also is less susceptible to noise. The mode uses AC coupling capacitors and 8B/10B signaling. Devices automatically detect whether AC mode or the standard DC mode is in use. Both modes now handle multibit skewing.
The new Ganging Mode lets a 3.0 device with a 16-bit link split the connection into a pair of 8-bit links. This is handy when interfacing a pair of 8-bit peripherals to a host without the need for a switch.