Networking

The ETRAX 100 LX: A Linux PC on a chip

Take a look at how this little Linux chip could impact network devices in the near future.

There is no question that electronic components are shrinking. Just take a look at the cell phone market and how ridiculously tiny some cell phones have become. Another example of how tiny electronic components are becoming is a wristwatch that was demoed at COMDEX this year that featured an integrated Palm operating system. When I saw this watch, I was stunned by the fact that it was possible to cram all of the necessary components into such a small space. However, a company called Axis has gone even further by releasing an entire PC that’s integrated into a single chip. In this article, I’ll introduce you to the ETRAX 100 LX and share some of the secrets behind this remarkable technology.

What's the point?
Sure, it’s impressive to integrate an entire PC onto a chip, but what would the average consumer do with the chip? The truth is that the chip isn’t intended for the average consumer but rather for companies that want to create embedded devices.

If a company were looking to develop an embedded computing device, the ETRAX 100 LX chip would be ideal in many situations. Because the entire operating system and just about all of the mandatory components are integrated onto a single chip, companies can develop embedded devices much more quickly and cost-effectively. Furthermore, because Axis has already thoroughly tested the ETRAX 100 LX chip, companies have less risk of design errors than they would have if they were to design an embedded device completely from scratch. In addition, because most of the critical components are embedded into a single chip, there’s much less risk of electromagnetic interference between the major components than there would be if the components weren’t integrated.

The chip's design
This amazing chip is a mere 27 x 27 mm. For those of you who don’t speak metric, 27 mm is just under 1.25 inches.

The chip contains the ETRAX 100 LX system, 2 MB of flash memory, 8 MB of SDRAM, an Ethernet transceiver, reset circuitry, and about 50 or so passive components such as transistors, resistors, and so on. These passive components are used to connect the various major components to each other.

The chip is designed to operate with a 3.0 to 3.6 VDC (Volts DC) power supply and to consume 1.2 watts of power. The power supply is attached to the chip via some of the chip’s pins. The chip has 256 pins in all, and the pins are used to connect a power supply and a variety of I/O devices. If you are interested in getting an ETRAX 100 LX chip and building an embedded device of your own, you can find the complete pinout at Axis’s Web site. There, you’ll find that the ETRAX 100 LX chip has pins for an RJ-45 connector (used for the onboard 10/100 Ethernet transceiver), four asynchronous serial ports, two USB ports, two parallel ports, and two IDE ports.

If you prefer to use SCSI rather than IDE, the chip does support SCSI devices. The chip contains two narrow SCSI ports, which can also be used as a single wide SCSI port. Another interesting feature of the chip is that although it has 8 MB of SDRAM integrated into the chip, there is room for expansion outside the chip. You can use some of the chip’s connectors to connect additional SDRAM, flash, EPROM, or SRAM.

The ETRAX 100 LX chip was also designed with high-speed networking in mind. The ship supports up to 200 MBps network connections (100 MBps Ethernet operating at full duplex). Because the operating system exists on the same chip as the Ethernet transceiver, the chip can take advantage of its full bandwidth. There are no bottlenecks present that would prevent the chip from being able to supply the network connection with data fast enough.

Speaking of the chip’s operating system, the chip runs a real Linux kernel, Linux 2.4 to be exact. Most other Linux-based embedded devices rely on uClinux patches rather than a true Linux kernel.

In case you’re wondering how Axis managed to cram so many components into the ETRAX 100 LX chip, they used a technique called high-density packaging to create a multichip module. High-density packaging allows for the integration of what’s called “naked dies.” “Naked dies” simply refers to bare chips without any type of housing. Therefore, components such as memory chips are stripped bare and integrated into the main ETRAX 100 LX chip. The fact that these individual components don’t require housing means that the finished product can be smaller, lighter, and more cost-effective than it would be if individual chips were used.

What's missing?
After reading all of the technical specs that I’ve thrown out, you may think that the ETRAX 100 LX chip has it all. There are a few things missing, though. As I read through the technical specs, I noticed that the chip doesn’t have any pinout options for keyboard, mouse, or video. If you wanted to use such devices, you’d probably have to devise a way to attach them through the available connectors. For example, you might be able to attach a keyboard to the USB port.

Building a PC
You might, at this point, be concerned about the chip’s usability. For example, the first time that I heard of the chip, I wondered if it was “really” a PC on a chip. The fact is, though, that minimal additional components are necessary for making an integrated, network-enabled device.

According to the Axis Web site, it’s possible to create a single-port serial server by combining the ETRAX 100 LX chip with an RS-232 transceiver and connector, an RJ-45 connector, a reset switch, power logic, a 20-MHz crystal oscillator, and a few passive components. In fact, AXIS actually posted the schematics for such a device on its Web site. While the schematic may look complex, it is nowhere near as complex as the schematic for even a simple PC.

Availability
Axis began shipping the ETRAX 100 LX chip in limited quantities in March 2002. The company began volume distributions in October 2002.

As you can see, the ETRAX 100 LX chip is quite an accomplishment. With it, you can create simple devices that use only the bare minimum of components and store applications within the onboard 2 MB of flash memory, or you can create an entire PC with attached storage devices and I/O ports.
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