MDK-ARM Keil, MDK-ARM Datasheet - Page 139

• Manufacturer Part Number: MDK-ARM
• Description: KIT REALVIEW MCU DEVELOPMENT
• Manufacturer: Keil
• Type: Compiler and IDEr

Specifications of MDK-ARM

• For Use With/related Products: ARM MCUs
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Getting Started: Building Applications with RL-ARM
139
In
, the Audio Class
usbcfg.h
support has been enabled, and
Endpoint 3 is used for the
streaming audio data. As in the
HID class configuration,
information is sent in the form
set_request and get_request
control transfers on Endpoint 0.
The Device Descriptors are held
in
. The descriptors
usbdesc.c
define three interfaces: an Audio
Class Control Interface (ADC
CIF) and two Audio Class Streaming Interfaces (ADC SIF). One streaming
interface is configured as an output and one as an input.
A typical application could use the OUT isochronous pipe to drive a speaker via
a Digital-to-Analog Converter (DAC). In the
file, the Endpoint 3
usbuser.c
callback handler is used to receive the data packet. It transfers data to a buffer
using the CPU or DMA unit, if one is available. The Audio Class driver in RL-
USB installs a Fast Interrupt Request (FIQ) interrupt. This is used to write the
data to the DAC and reproduce the audio stream. The Audio Class also supports
feature requests, which are sent on Endpoint 0. These are used to pass control
information from the host application to the audio device. In the speaker
demonstration, the Audio Control Interface is used to control the volume level
and mute function.
Exercise: Audio Class Example
This example demonstrates a speaker application using the Audio Class.
Composite Device
As we have seen in the previous sections, the RL-USB driver supports three of
the most useful USB classes. In some applications, it may be necessary to
combine the functionality of two or more classes. For example, you may wish
your device to appear as a Mass Storage Device so that you can easily transfer
large amounts of data. It may also be useful for the device to appear as a HID
device, in order to send small amounts of control and configuration data. RL-
USB is designed so that each of the supported classes can be combined into one
application to make a composite device.