To stay “connected and in touch,” consumers
increasingly rely on their portable devices, ranging
from smart phones, personal media players, and digital
cameras to emerging solutions like electronic notebooks.
Today’s handhelds serve multiple roles and
offer various functions that translate into a host of
storage, feature, and technology challenges depending
on the end application.
At the same time, portable designers are under
increased cost and time-to-market pressures, struggling
to deliver new features and keep pace with rapidly evolving
standards in the price-sensitive consumer market.
Complicating matters further is the need to deliver all of
these features without sacrificing battery life.
Field-programmable gate arrays (FPGAs) are traditionally
seen as the best vehicle for getting designs to market
fast. Yet use of the technology has been limited to prototyping
due to power consumption and cost concerns.
Over the past few years, however, design advances
have pushed FPGAs into high-volume portable designs.
Also, emerging solutions are helping designers reduce
cost and increase battery life. Flash-based FPGA solutions,
for example, eliminate power-hungry configuration
memory and the leakage current associated with
SRAM-based solutions.
FPGAs are available with static power as low as 5 mW
and active/dynamic power as low as 25 mW—power consumption
rivaling custom ASICs and application-specific
processors. Moreover, their inherent programmability
enables designers to engage in platform-based design.
This lets OEMs work from a single base
platform and add or strip out features to
satisfy multiple price points. The ability
to leverage hardware and software
design costs across multiple product
models leads to greater economies of
scale for portable designers.
THE PORTABLE STORAGE LANDSCAPE
• Increasing digital content in
today’s portable devices ups the
demand for greater storage capability.
As a result, portable storage can
account for a large majority of the power
consumed in an electronic device.
From hard-disk drives (HDDs) to flash
devices, portable storage applications
can leverage FPGAs for lower cost,
increased flexibility, and longer battery life. Application
processors, which are used to run the operating system
(OS) and the application software, have predefined interfaces
and generally are unable to adapt to rapidly changing
market requirements.
Thus, key areas where FPGAs can deliver muchdesired
flexibility include storage, processor bridges
and controllers, and connectivity interfaces. In these
applications, flash-based FPGAs are able to reduce
power consumption while supporting myriad storage
interface standards.
A variety of storage solutions, broadly classified as
flash storage devices and HDDs, is available for use in
today’s growing array of electronic devices. Portable products
requiring the high-storage capacity of an HDD solution,
such as video recorders and camcorders, will
employ one of two types of controller. The first is an integrated-
device-electronics (IDE) controller, which is based
on parallel or serial ATA standards. The second is a consumer
electronics ATA (CE-ATA) controller—a common
standard among small form-factor devices like portable
media players and handheld devices.
Flash-memory usage is also expanding, giving rise to
another set of storage interfaces. Multiple memory-card
formats, such as Secure Digital (SD) and the very small
and removable Compact Flash (CF) solution, along with
NAND flash controllers, are the primary interfaces used
in the flash market.
Handheld devices may either use a combination of
these interfaces or require just one interface for a particular application. Either way, semiconductor solutions
must provide the flexibility to implement any number of
interface options.
Application processors traditionally provide support
for a select number of storage interfaces. However, a
new trend in handheld design pairs application processors
with ultra-low-power FPGAs, using the FPGA to provide
the bridging function and extend the processor’s
storage interface support (Fig. 1).
STORAGE IMPLEMENTATION
• When implementing
a storage system, it’s important to focus first on basic
architecture choices. First, which processor will be
used? In the competitive portable market, there are usually
several leading processor candidates, and often the
designer’s choice can be influenced by multiple factors—
from technical requirements like performance, size, and
power profile to previous design experience using that
particular processor.
Consequently, designers must carefully evaluate their
design goals. Does the design depend on a previous
architecture and, therefore, is it required to be backwardcompatible?
Do the engineers have the flexibility to
choose the processor with which they have the most experience?
Does the design require low power? Certainly, in a
portable application, the processor’s power consumption
and efficiency will be key factors in the decision.
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