Integrated packet bus drives toward riser-card spec

Integrated packet bus drives toward riser-card spec
SAN JOSE, Calif. — The Advanced Communications Riser Special Interest Group showcased its Integrated Packet Bus (IPB) technology at the Platform Conference last week, hoping to throw more OEM weight behind its next-generation riser-card spec.

The AMD-led group, an open-standard consortium, was formed to address the higher levels of integration in communications chip sets that began to hit the market last year.

In 2000, vendors started to add Ethernet capability to new chip sets, augmenting support for soft modems, soft audio and other PC client communications functions. Those enhancements accelerated the need for a riser-card standard to pull them together cost-effectively.

Though Intel led CNR, a rival consortium and spec that relied heavily on Intel's Universal Serial Bus (USB) technology, the industry largely moved to the Advanced Communications Riser spec in 2000. ACR is an open platform that has seen its Special Interest Group quickly grow to over 50 members. Besides AMD, the consortium has heavyweights like 3COM, Conexant, Lucent Technologies, Motorola, Texas Instruments and VIA as founding members.

Low-cost solution

The spec promises a flexible, lower-cost solution for integrated local-area network (LAN) and wide-area network, multichannel audio, HomePNA, Pots modem, broadband and other communications functions, while freeing up PCI expansion slots.

Technologies like AC-Link are beginning to run out of steam, the group said, causing the need for a new bus. "Graphics were really beginning to hog the bus, and it was a real strain on PCI. The transition to 3-D graphics really caused this shift," said Conrad Maxwell, a manager of product and technology planning who works for Conexant Systems Inc. "So we saw the need for a new platform.

"People say, we already have AC-Link in core-logic devices, why not use it for broadband? But if you go through the numbers, and look at the data rate for [digital subscriber line], it's too high for AC-Link, it's too high for USB, and therefore, a dedicated bus is needed," Maxwell said.

That bus, the IPB, was developed in conjunction with the ACR 1.0 spec, and lets the host system CPU directly process the communications stream.

The bus is a full-duplex, time-division multiplexing design that consists of a clock signal for each direction of transfer, two data bits in each direction and up to two framing signals, with up to 80-Mbit/second data transport. In all, ACR 1.0 supports an improved pnp for AC-Link, two LAN ports, one broadband port (the IPB) and legacy AMR.

Strauss said, "We left enough flexibility to maneuver the data-rate improvements and other advances like DDR [double-data rate], which will be addressed in future revisions."