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Flash memory persistence tech supports super low voltage devices

Feb 18, 2011 — by LinuxDevices Staff — from the LinuxDevices Archive — 1 views

Researchers from the University of Massachusetts and Texas A&M have developed a way to use flash memory in gadgets that use low power or have no batteries at all. Applied to a sensor-monitoring application using a 1.8 Volt microcontroller, the researchers' “persistence” technique reduced overall energy consumption by 34 percent, says the researchers.

Researchers from University of Massachusetts Amherst and Texas A&M University have succeeded in writing information to flash memory under low-voltage conditions, paving the way for a new generation of low-power gadgets that can store data. Their paper, "Exploiting Half-Wits: Smarter Storage for Low-Power Devices" was presented Feb. 16 at the USENIX File and Storage Technologies Conference in San Jose, Calif.

Flash memory generally requires 2.2 to 4.5 volts, which makes the technology unusable in devices using low-power microprocessors, the researchers write. For example, the embedded-oriented, Texas Instruments MSP430 microcontroller used in the researchers' demonstration runs on as little as 1.8 Volts.

A number of memory manufacturers have started building low-power flash solid-state-drives for use in embedded storage systems, such as Sandisk, or Greenliant with its NANDrive GLS85LS. Greenliant targets embedded devices in enterprise, industrial, automotive and networking applications. Intel also recently announced an SSD 310 device that can be used in industrial embedded applications.

In general, low-voltage embedded designers have opted to either boost CPUs to meet flash memory's minimum voltage requirements, or just not use flash memory at all, the researchers explain in their paper. Tablets and netbooks can support flash memory because they have the room to support separate power rails for the CPU and flash memory. That is not possible on smaller gadgets where the flash memory is integrated within a microcontroller. If the battery can support both, that's fine, but generally the batteries are also much smaller in size and power. 

Persistence beats the low-voltage challenge

One way to effectively write data to flash memory when running on less than the minimum required voltage is "persistence," according to the project's lead researcher, Mastooreh Salahegheh (pictured). The software-only coding algorithms exploit "the electrically cumulative nature" of half-written data based on a quantum mechanical phenomenon called tunneling.

In this case, outside electrons travel to the chip a little at a time and accumulate since it's not being used. Once enough electrons have been collected, there's enough power to meet specifications to write data for that instant, the researchers say.

Obviously, this process won't have good performance or efficiency, but if the goal is to conserve power, it accomplishes it readily, according to the paper. On a sensor-monitoring application using the MSP430, researchers claimed they used persistence to reduce overall energy consumption by 34 percent.

"Our evaluation shows that tightly maintaining the digital abstraction for storage in embedded flash memory comes at a significant cost to energy consumption with minimal gain in reliability," says the paper.

A persistence method like this may be useful for a number of small devices, such as remote control key fobs or digital picture frames. It can also be useful on devices that currently don't have batteries, such as RFID tags and electronic passports. With the persistence technique uncovered by Salajegheh's team, embedded application designers can fit non-volatile storage inside these small devices.

The team's Salajegheh, Kevin Fu, and Erik Learned-Miller work at University of Massachusetts Amherst. Yue Wang and Anxiao Jiang from Texas A&M make up the remainder of the research team.


A PDF of the UMass and Texas A&M researchers' paper, "Exploiting Half-Wits: Smarter Storage for Low-Power Devices," may be found here.

Fahmida Rashid is a writer for our sister publication eWEEK.

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