Got any Gumstix? A look at shrinking SDR
This is based on an interview conducted by Chris Ciufo originally run in our sister publication, DSP-FPGA.com. The story, as told by PrismTech SVP of corporate development Steve Jennis and Gumstix president and CEO Gordon Kruberg, is compelling in that a Software-Defined Radio (SDR) package that normally took 20 MB of memory was shrunk to run in 1 MB, and then placed on the diminutive Gumstix hardware. This Software Communications Architecture (SCA) implementation captures what we consider to be the power and potential of small form factors – a full-function application in a much smaller solution than what is usually seen.
SFF: This appears to be a fully functional SDR implementation, but it's nowhere near the size we've seen before. Tell us what we're looking at.
JENNIS: SDRs ‚Äì and military programs in particular ‚Äì have always suffered from the label that the SCA is fat and heavy. Many implementations of the SCA run in 10-20 MB of memory, which has a direct negative impact on SWaP [Size, Weight, and Power] consumption. The idea is to reduce SWaP.
When we came to market in 2007 with the Spectra OE SCA implementation in a footprint of under 1 MB of memory ‚Äì including the ORB [Object Request Broker], CORBA [Common ORB Architecture] Services, and Core Framework ‚Äì a lot of people raised their eyebrows. Suddenly, the whole prospect of getting the SCA down to a handheld or even smaller looked like it had become a reality.
As SDR makes its way into cellular and consumer communications, moving into smaller form factors that can be battery powered is a significant breakthrough. We are very happy to work with Gumstix to illustrate how SDR technology is viable in a handheld or smaller form factor.
SFF: Why use the Gumstix form factor?
KRUBERG: We are less pervasive than other small form factors like PC/104. But we're also a tiny fraction of the size and a fraction of the power requirements when it comes to actually going into a real mobile device. Having something that is so power efficient is what drives use of the Gumstix. [Editor's note: See Figure 1 for an example of a Gumstix motherboard.]
The differentiating feature of our form factor is that we picked the smallest size we could and still implemented a "nonembedded" Linux device. It's a complete Linux implementation, but somebody who is used to working with a full root environment can have as big a root file system as they want and can pack whatever they want into it. Their code can be recompiled from an x86 desktop or server environment.
JENNIS: From our perspective, there's a big trend toward using open source operating systems, so Linux is important. There's also a big trend toward using COTS products rather than a hand-built, custom-designed product.
You are going to need something that is small, commercially available, low cost, and runs an open source operating system. All these factors would point radio vendors to Gumstix.
SFF: What's the processor on a Gumstix module?
KRUBERG: In this application, it's a PXA270 Marvell XScale with a full MMU, supplemented by a Marvell chipset. Our boards run from 400-600 MHz, and the CPU can operate on less than 1 W and as low as -25 ¬∞C. Each Gumstix board itself is 20 mm x 80 mm, which is really just a fraction larger than an average stick of chewing gum, depending on which connectors you've got on it.
SFF: Does the Gumstix module need a hard disk or large flash storage?
KRUBERG: If you wanted, you could mount a network root FS, or have a hard disk connection over the USB port sitting right there on the desk. In this application, the Spectra OE runs in the nonvolatile memory of the Gumstix motherboard itself, so it all resides onboard as opposed to running off of a hard disk somewhere.
Gumstix verdex motherboards have 32 MB of flash and 128 MB of RAM, so they are not crippled as fas as memory is concerned. User-configurable I/O is available via various other daughtercards. In fact, you can stack cards on each side of the motherboard and essentially end up with a "pack of gum."
SFF: How much does a Gumstix module cost?
KRUBERG: The motherboards right now range from $99 to close to $200 each. We publish pricing and technical information online at www.gumstix.com.
SFF: Can you summarize the value proposition of the PrismTech/Gumstix implementation?
JENNIS: The real secret is the marriage between the Gumstix motherboard and the Spectra OE SCA Bundle. You get SCA 2.2.2 compliance with all the pieces required to implement the SCA on a module that is small, off-the-shelf, runs in an open source environment, and low power/low cost. We think it's a big step on the way to taking SDR out of the back room and down into the handset. And it's only when it gets into commercial use where everyone benefits from the economies of scale they are looking for. ‚û§
Steve Jennis is SVP of corporate development at PrismTech, based in Burlington, Massachusetts. Prior to joining PrismTech in 1994, he was the general manager of Texas Instruments' Computer Products Division. Steve has a degree in Physical Sciences from Loughborough University in the United Kingdom.
W. Gordon Kruberg is president and CEO of Gumstix, based in Portola Valley, California, with experience managing investments in software, biotechnology, and medical technology startups. Gordon holds an AB in Human Biology, an MS in Industrial Engineering from Stanford University, and an MD from Northwestern University.PrismTech