Inside Oxford Semiconductor & The Oxford 911 FireWire Bridge

Ask any knowledgeable consumer in the market for FireWire storage for advice and youill hear, "get something with the Oxford 911 chipset, itis the fastest." Then youill say, "What the &$@% is that?" Well, I recently spoke with James Lewis the president of Oxford Semiconductor, the company responsible for this burst of speed, to find out.

Oxford got its start in England, making application specific integrated circuits (ASICis) for customers to their specifications. As the company began to build and market its own standard chipsets, USB was all the rage.

"USB was coming along at that point, but we could see some issues with USB in that there were lots of manufacturers moving into that field, and support issues were not terribly good. As we guessed, the chip prices really got fought down before the market even developed fully. We were glad that we overlooked that one. At that point the specs for FireWire, for 1394 were just being defined, so we decided weid be first to market with that rather than last to market with USB." The company didnit ignore USB entirely though. "The onset of legacy free PCis has meant thereis been a big aftermarket requirement for serial and parallel ports to connect. [...] Weive had our chips used in things like serial to USB adapters for the iMac."

Right now though the focus is firmly on FireWire. The 911 is the companyis 2nd generation IDE to FireWire bridge chipset, the first being the 900 which entered the market at the tail end of 1999. "[It] was quite a major step in terms of integration because it has a RISC processor, an ARM processor." ARM being the same Apple held British company responsible for the StrongARM processor that was used in the late Newton PDA.

The Benchmarks

Mac performance site, Accelerate Your Mac has been following the emergence of the 911 with benchmarks and real word tests so you can see the differences between the theoretical maximums mentioned here, and the level of performance you can expect. There are also two build guides for hard drive case kits from Other World Computing and TransIntl:

Transintl.comis Portable FireWire Case Kit
OWCis Elite FireWire Case Kit
OWCis FireWire Hard Drive Case Benchmarks

Are devices with this chipset commanding a price premium? It doesnit seem to be the case, although a cursory examination of the two manufacturers mentioned above plus LaCie revealed little. Comparison between manufacturersi products wouldnit necessarily isolate the 911is cost since there are other variables like case design, economies of scale, etc. Other World for example, doesnit seem to be selling identical drives using old and new chipsets. LaCie doesnit mention the 911 at all, although listing a sustained transfer rate of 35MB/sec is a telltale sign that somethingis improved. If a manufacturer doesnit specifically mention the 911 in its marketing, it might be worthwhile to ask. As of this writing, you can expect to pay around $240 US for a 40 GB external drive with a 911 chipset.

So what is the 911 and what exactly does it do? On one end thereis the FireWire connection, at the other end is the IDE interface, which on the 911 is an ATA/66 interface. So at each end thereis data in different formats and command sets. Right in the middle sits a buffer (meaning memory) and a buffer manager. The data being transferred isnit altered or converted like an audio CD track to an MP3 for example. What happens is more akin to taking a text file and converting it to HTML. ATA commands are stripped out, the data is passed along, FireWire commands are inserted and vice versa.So where do things get faster? First, a quick bit of math. FireWire transmits data at a maximum of 400 megabits per second. At 8 bits to a byte, that translates to 50 MB/sec. Thatis the ceiling for the version of FireWire used in every Mac to date. The older 900 chip operates in DMA mode meaning about 15 MB/sec. This means drives up until now were only using 30% of the bandwidth available. Since the 911 uses ATA/66, it operates at around 42 MB/sec. Thatis 84% of the available bandwidth, nearing a threefold performance increase (all based on theoretical maximums).

This is done with two processors, one being an ARM 7 which is a "soft" processor. Think of it as a very simple example of what Connectixis Virtual PC is; software code that acts like a piece of hardware. The ARM 7 resides in less than 512 K of flash memory. Itis customizable and hence upgradeable via the FireWire port, and it handles the management of things like boot up. Thereis also a coprocessor in hardware to do time critical command interpretation and translation. As a result, the ARM only needs to use about 30% of its processing power at any given time.

Oxford is demoing a version of firmware that lets the ARM do more: administering a filesystem. Why should they want to do this? Connect a FireWire hard drive to a Mac, and the Mac administers the files, right? Sure, but what if you want to access data on the drive when itis not connected to a computer?

Add an MP3 codec and some audio chips and youive got a hard drive that doubles as a standalone MP3 player. "This merges into Appleis iTunes very well," said Mr. Lewis. "Obviously iTunes allows you to manage MP3 files on your Mac. What we can do now is just write those MP3 files from [the] directory structure on your Mac, dump them into the MP3 player in seconds." Remember now, this is at 42 MB/sec FireWire speeds, not USB. Could this setup conceivably enable a hybrid MP3 player and FireWire hard drive? Yes. That means no more synchronizing with iTunes at all. Keep the iTunes library on this hybrid device. Use iTunes when itis connected to a Mac or unplug it, and use it as a standalone player.

By sticking to the open specification of FireWire, they havenit needed any assistance from Apple. "Weive obviously had discussions with Apple, just to make them aware of what weire doing and allow them to test the chips. Theyive kept a healthy interest in everything weive done so far, and stuff that weire doing for the future."

And what does the future hold for Oxford Semiconductor? Theyire working on some Bluetooth projects, and theyire looking into USB 2.0. But with most of their engineering effort behind FireWire, new things are in the works. "If you look at where the 1394 spec is going, thatis where weire going as well." With the 911, the bridge is no longer the bottleneck. Using 400 Mbps FireWire, and getting maximum throughputs of 42 MB/sec, "thatis more or less the maximum that disk drives will give you at the moment." But the 911is can, because of their IDE controller, host both a master and a slave device, or two hard drives. Thatis one clue about future devices. Another has got to be the impending arrival of 1394b which is FireWire at 800 Mbps.

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