Mass Storage Basics - USB Mass Storage: Designing and Programming Devices and Embedded Hosts - page 6

Figure 1-2: To access generic USB mass-storage devices, an embedded
system must contain a USB host controller, which can be on a separate chip or
embedded in a microcontroller.

• A USB host controller, which can be embedded in a microcontroller chip
or on a separate chip that interfaces to the CPU, microcontroller, or
other intelligent hardware.
• A generic hard drive, flash drive, or other media connected to a USB port
on the host.
The hardware or firmware in an embedded USB mass-storage host must
provide the following functions:
•

Issue USB requests and initiate other events on the bus to identify
attached devices and manage traffic and power on the bus.

• Issue USB mass-storage requests that ask for status information or specify

actions for the device to perform.

• Issue SCSI commands in USB transfers. The commands read and write

blocks of data in the storage media, request status information, and con-
trol the device operation.

• Support a file system to access files in the media.