Embedded Hosts - USB Mass Storage: Designing and Programming Devices and Embedded Hosts - page 259

11
Embedded Hosts
With support for mass storage, just about any USB host can communicate
with off-the-shelf mass-storage devices, including hard drives and flash
drives. This chapter looks at what's involved in designing and programming
an embedded system that functions as a USB host. Much of this informa-
tion can be helpful to device designers as well, especially the information
about common device problems that hosts experience.
Inside an Embedded Host
As Chapter 1 explained, a host's function is in many ways a mirror image of
a device's function. All USB hosts must detect device attachment and
removal and manage power and bus traffic. Chip vendors typically provide
example firmware for performing these tasks.
On detecting a device with an interface descriptor that specifies the
mass-storage class, a host that supports mass storage should examine the
interface descriptor and the device's response to a SCSI INQUIRY com-
mand to learn which SCSI command set the device claims to support. The
host can then proceed with other mass-storage communications. A host that