Information Technology Reference
In-Depth Information
If the device has a Universal Serial Bus (USB) interface, any PC or other
USB host can access the storage media. Generic USB mass-storage devices
include the hard drives, flash drives, CD drives, and DVD drives available
from any computer-hardware store. Table 1-1 lists popular device types.
These devices have just one function: to provide storage space for the sys-
tems they connect to.
Another type of USB mass-storage device (or storage device for short) is the
special-purpose device with storage capabilities. For example, a camera can
capture images and store the images in files. A data logger can collect and
store sensor readings in files. A robotic device can receive files containing
configuration parameters. With the addition of a USB mass-storage inter-
face, any of these devices can use USB to exchange files with PCs and other
USB hosts.
Generic storage devices are readily available and inexpensive. Unless you're
employed by a storage-device manufacturer, there isn't much point in
designing and programming your own generic devices. But special-purpose
USB storage devices are useful in many embedded systems, including
one-of-a-kind projects and products manufactured in small quantities.
Another option for some systems is to add USB host-controller hardware
and mass-storage firmware. The embedded system can then store and read
files in off-the-shelf USB storage devices.
Benefits
Adding storage-device capabilities to a system has several benefits:
•
With a USB device controller, a system can make the contents of its stor-
age media available to any PC or other USB host computer.
•
File systems provide a standard way to store and access data. A PC or
other USB host can format the media in a USB storage device to use the
FAT16 or FAT32 file system. When the device is connected to a PC, the
operating system enables reading and writing to files. Users can access the
files without having to install and learn a vendor-specific application.
•
Storage media is readily available. Flash-memory cards are convenient
and have enough capacity for many applications. Some cards require only
a few port pins to access. Devices that need large amounts of storage can
interface to hard drives.
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