Electronic Design

What Can You Build With Ethernet, USB, And An Arm?

Tucked away in a couple of smaller booths at January’s International Consumer Electronics Show in Las Vegas was a pair of companies with an interesting approach to network attached storage (NAS). One was PogoPlug. The other was Ctera. They have slightly different business models, but the hardware looked similar. In fact, it looked a lot like Marvell Semiconductor’s SheevaPlug (Fig. 1).

The SheevaPlug is essentially a small PC that plugs into a wall socket. It is based on the Sheeva processor from Marvell, which is built around an Arm core that Marvell designed instead of something like the Cortex M3 that Arm created (Fig. 2). This allows Marvell to tailor its design while retaining access to all the Arm-related development tools.

The SheevaPlug runs a 1.2-GHz 88F6281 Sheeva processor with 256 kbytes of L2 cache. The module also features 512 Mbytes of flash and 512 Mbytes of SDRAM. That’s comparable to any netbook on the market and a pretty hefty system compared to even a desktop PC a few years ago. Gigabit Ethernet and a USB 2.0 host interface round out the peripherals.

Unlike the shipping end-user products, the Sheeva- Plug also has a header for a debug board that adds a USB JTAG interface and access to the chip’s secure digital input/output (SDIO). Of course, once Linux is loaded on the system, it’s possible to perform application debugging via the Ethernet port.

The whole package draws less than 5 W running full tilt. It can draw considerably less when idling, and it can power down the USB peripherals as well. Outfits like PogoPlug load in file server software and allow customers to plug in one or more external hard drives. Their claims to fame are ease of use and added services such as Internet backup.

Marvell delivers the SheevaPlug with a Linuxbased software stack that includes Marvell’s Raindrop application programming interface (API) and a Javabased OSGi Alliance stack. OSGi provides its own plug-in architecture, while the Raindrop API enables third parties to deploy applications via the Internet in a secure and resource-defined fashion.

The Raindrop API will, in theory, provide an iPhone store capability. The idea is to provide control over what the downloaded services have access to as well as communication with remote services without the need to write all this code from scratch.

It will be interesting to see how this system evolves as its success depends on adoption of products from companies like PogoPlug. Keep in mind that not all storage and services have to reside on the plug-in device since they can be accessed via the Ethernet connection instead of the USB interface.

Likewise, it’s possible to connect any kind of USB device to the SheevaPlug. For example, Acces I/O offers a range of external USB boards for control and data acquisition (Fig. 3). Applications must still be written for the SheevaPlug to handle these devices, but typically the interface is a standard USB interface such as a virtual serial port. It is even possible to write an application that can provide remote access to the device. Why use a PC or embedded computer to monitor a system when all one needs to do is cable together one of these modules plus an Acces I/O board? USB opens up a range of possibilities, such as

USB-based display adapters, printers, cameras, or touchpads. An external USB hub allows more than one device to be added to the mix. NAS devices are just one possibility. So what will you do with the $99 SheevaPlug?

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