Advanced Micro Devices Inc. is quietly taking the next steps in its journey from component supplier to technology provider by trying to broadly license its proprietary Lightning Data Transfer (LDT) bus technology.
When introduced last October at the Microprocessor Forum in San Jose, AMD positioned the bus as little more than a way to provide a high-bandwidth path toward multiprocessing systems in AMD-based PCs, workstations, and servers.
But company executives said last week that they are positioning the bus as a top-to-bottom approach to consolidate the circuitry not only in the traditional PC and enterprise spaces, but in embedded applications as well. To date, AMD said 40 hardware companies have signed on as LDT partners.
"Our goal is to evangelize [LDT] as an industry standard," said Charles Mitchell, senior technical evangelist at AMD, Sunnyvale, Calif. "Three years ago, this was designed as a north-bridge/south-bridge [chipset] technology. Now, it's much bigger than that; it's also about how we handle I/O inside a multiprocessing environment."
AMD is trying to establish LDT as a universal interconnect, a single bus for what Mitchell calls "the bus hodge-podge" of PCI, Accelerated Graphics Port, DRAM, and other dedicated high-bandwidth buses inside a computer.
According to Mitchell, LDT design work is taking place in PC chipsets and multiprocessor chipsets, but the bus is also being considered as an integrated I/O link within embedded RISC microprocessors, embedded RISC chipsets, PCI-X bridge chips, and OEM routers and switches.
Mitchell declined to name AMD's partners or disclose how far the designs have proceeded. "We're trying to persuade the OEMs to come forward and talk about this," he said.
Mitchell also said he's trying to make it "explicitly clear" that LDT's royalty-free license is not designed to generate profits, nor is it intended as a means to barter for additional intellectual property.
Whether the industry shares AMD's vision is a cloudy issue. Dean Klein, vice president of the integrated products group at Micron Technology Inc., Boise, Idaho, praised the new bus, even deeming it a potential replacement for PCI.
Suresh Pannikar, director of product marketing at I/O provider Mylex Corp., Fremont, Calif., said he was unaware of any licensing activity, but acknowledged that the license would first have to be established to enable product development.
Analysts were hesitant to predict the outcome of AMD's strategy, but confirmed the LDT's direction. "I think that's what [AMD wants], to make it a top-to-bottom solution, at least because it's a best-fit for [an OEM's] engineering efforts," said Dean McCarron, an analyst at Mercury Research Inc., Scottsdale, Ariz. "The question's whether they can make it cheap [to purchase]; it's definitely in the development stage."
Two potential obstacles exist, McCarron said: cost and third-party support. The latter hurdle, at least, could well prove to be merely a crack in a well-paved road, he said. "OEMs seem to be doing whatever AMD asks, bending over backward to keep them in the market. What a difference three or four quarters makes."
The LDT technology was originally designed to provide high-bandwidth connections between the north bridge of a chipset and other bridge chips, whether it was the south bridge or some specific I/O bridge, such as a dedicated Infiniband host controller. The bridges could also be daisy-chained across a single LDT link.
But AMD sees the technology as being extended "up" into a point-to-point connection for servers, eliminating the microprocessor bus entirely. For 32-bit Athlon multiprocessor systems, Mitchell disclosed that a superset of the LDT specification, or "coherent LDT," has been developed for non-uniform memory-access matrixes, where arrays of processors can access dedicated local memory as well as "distant" memory that is attached to other CPUs.
Mitchell also said that the forthcoming Sledgehammer 64-bit microprocessor will contain an integrated north bridge with an LDT connection.
The LDT bus could be extended "down," as well, into low-cost integrated systems, Mitchell said. While he did not announce products or timetables, Mitchell said AMD is planning a single-chip integrated microprocessor, similar in concept to Intel Corp.'s forthcoming Timna chip.
LDT's one-size-fits-all implementation comes from its flexibility. The bus consists of two unidirectional streams, either 2, 4, 8, 16, or 32 bits wide in each direction. The appropriate bit width is negotiated at initialization, either during a boot or a hot swap, and commands, data, and bit addresses move through the same pipe in 4- to 64-bit packets, giving priority to isochronous streams.
Mitchell said the bus has been designed with a standard "Plug and Play" header, supported by Microsoft Corp.'s operating systems.