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MSP430 USB Software Design

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5 MSP430 USB Software Design

Most of the MSP430 USB software documentation is located in the USB API Programmer's Guide, located

in the USB Developers Package. Therefore, this section is only an introduction.

5.1 How to Choose a USB Device Class

Tradeoffs between the three device classes are shown in Table 5. (Plain text indicates advantages or

neutral comments, and italic text indicates possible disadvantages.)

Table 5. Device Class Tradeoffs

CDC HID MSC

Characteristic

(Communications Device Class) (Human Interface Device Class) (Mass Storage Class)

The interface

• Virtual COM port • A human interface device • Storage volume

generated on

the host

Industry Storage volumes are common in the

• COM ports are common in the • Unlike COM ports or storage

expertise for this industry; widely-supported and well-

industry; widely-supported and volumes, HID interfaces are

interface understood

well-understood somewhat USB-specific, and

less known in the industry

Installation on

• Windows PCs must undergo a • Loads silently in most • Loads silently in most

the host

device installation process that operating systems – simply operating systems – simply

requires end user interaction.

(1)

begins working. begins working.

• Admin rights on this Windows • No driver files required • No driver files required

PC are required

• Despite the actual binary files

already existing in Windows,

the user must supply an INF

file

How the end

• An application on the host that • A custom application on the • The device mounts a storage

user interacts

interfaces with COM ports host that interfaces with HID volume onto the system;

with it

devices applications read and write

• The application might be

files on the volume.

custom, or any existing

application that uses COM • The application might be

ports custom, or any application that

reads or writes files

Driver

• Unless the INF file is WHQL • No 'uncertified' message is • No 'uncertified' message is

certification

certified (signed), Windows will generated generated

needs

report that the driver is

'uncertified'.

(2)

Code footprint

• Small code footprint (4-6K) • Small code footprint (4-6K) • Larger code footprint (8-15K)

and complexity

• Simple architecture • Simple architecture • Requires a file system,

increasing cost, size, and

complexity.

Throughput

• Fast (hundreds of KB/sec) • Slower (64 KB/sec) • Fast (hundreds of KB/sec)

• Uses bulk USB transfers. • Uses interrupt USB transfers. • Uses bulk USB transfers.

Good for point-

• Yes • Yes • No

to-point

communication

between host

and device

Good for bulk

• Yes • No • Yes

data transfer

(1)

This is the process that occurs the first time the device is attached to the host. In Windows, this process may begin with a

"Found New Hardware" dialog box. The user must locate the INF file provided by the OEM.

(2)

WHQL certification refers to Microsoft's Windows Hardware Quality Labs. See http://www.microsoft.com/whdc/winlogo.

Starting a USB Design Using MSP430™ MCUs SLAA457A–September 2013–Revised May 2014

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