ATmega32U4 USB音频示例说明书-USB迷|专注于互联网分享

2024年10月30日发(作者：严新林)

AVR298: USB Audio Demonstration with

ATmega32(16)U4

Features

•

Runs with ATMega32U4 Microcontrollers at 8MHz

•

USB Low Power Bus Powered Device (less then 100mA)

•

Supported by any PC running Windows

(98SE or later), Linux

or Mac OS

•

Less than 14Kbytes of Code Required

•

USB device with audio speaker and audio microphone

uction

This document describes a simple audio project. It allows to quickly test USB hard-

ware using the ATMega32U4 without any driver installation.

The reader should be familiar with USB Software Library for AT90USBxxx Microcon-

trollers (doc 7675, included in the CD-ROM & Atmel website) and the AUDIO

specification (/developers/devclass_docs/).

8-bit

Microcontrollers

Application Note

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re Requirements

The USB audio application requires the following hardware:

•AVR USB evaluation board (ATEVK527)

•AVR USB microcontroller

•USB cable (Standard A to Mini B)

•PC running on Windows

(98SE, ME, 2000, XP), Linux

or MAC

OS with an USB 1.1 or 2.0

host

•headset

-System programming and Device Firmware Upgrade

To program the device you can use the following methods:

•The JTAG interface using the JTAGICE mkII

•The SPI interface using the AVRISP mkII and JTAGICE mkII

•The USB interface thanks to the factory DFU bootloader and FLIP

(1)

software

•The parallel programming using the STK

500 or STK

600

Please refer to the hardware user guide of the board you are using to see how to program the

device using these different methods.

Please refer to FLIP

(1)

help content to see how to install the USB driver and program the device

through the USB interface.

Note: is software provided by atmel to allow the user to program the Atmel devices through the

USB interface (No external hardware required) thanks to the factory DFU bootloader.

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Start

Once your device is programmed with EVK527-ATMega32U4-usbdevice_audio.a90 or EVK527-

ATMega32U4-usbdevice_ file, you can start the audio demonstration. Check that your

device is enumerated as an audio controller (see figure 11), then you can use the kit as an audio

speaker and audio microphone.

Figure Enumeration

The figure below shows the ATEVK527 used for the demo:

Figure tration Board

USB

Microphone

Speakers

Board power = 3V

7820A–AVR–11/08

ation Overview

The USB audio application manages the data exchange between the PC and the PWM hard-

ware (speaker) and ADC hardware (microphone). When a sound is played on the PC, the USB

device receives a periodic unsynchronized OUT endpoints, and when the record microphone is

running then the USB device receives a periodic unsynchronized IN endpoints.

Figure ation data exchange

OUT endpoint

PC play

PCM 16bits mono at 32KHz

PWM

Speaker

9bits mono at 32KHz

IN endpoint

PC record

PCM 16bits mono at 8KHz

ADC

Microphone

8bits mono at 8KHz

During the USB enumeration, the USB device describes the frequency and the formats of the

audio data. In the demo, the data format used is the PCM, the speaker uses 16-bit mono at

32KHz, and the microphone uses 16-bit mono at 8KHz.

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As explained in the USB Software Library for AT90USBxxx Microcontrollers document (doc

7675) all USB firmware packages are based on the same architecture. This section is dedicated

to the audio module only. The customization of the files described hereafter allows the user to

build his own audio application.

Figure Audio Firmware Architecture

7820A–AVR–11/08

6.1audio_task.c

This file contains :

•timers initialization

•timers interrupts

•routines which collect and put audio data

Speaker

The main audio task gets the audio samples from endpoint OUT and put it in the RAM buffer.

The OSC value tolerance doesn't allow to have an exact 32KHz frequency for the speaker, so

the main loop adjusts the timer 1 interrupt to avoid losing a sample or underrun.

Timer 1 interrupt transfers the audio data from RAM to PWM (high speed timer). Timer 1 is

responsible for adjusting data flow with PWM bits resolution and volume requested by USB host.

Note:We use only 9 bits out of the 10 bits from PWM to avoid saturation of Operational Amplifier.

Microphone

Timer 0 interrupt is used to get the ADC value each 125µs (8KHz) and if the “endpoint IN” is

requested by the USB host, the value is put in this endpoint.

Figure ation data exchange

USB

Speaker

OUT endpoint

Audio taskRAM buffer

Interrupt

Timer 1

PWM

timer high speed

USB

Microphone

IN endpoint

Interrupt

Timer 0

ADC

This file contains all the routines to manage the EVK527 board ressources (Joystick, ).

The user should not modify this file when using the EVK527 board. Otherwise, he has to build

his own hadware management file.

6.3usb_specific_request.c

This file contains the routine which receives the audio control requests, like volume level and

mute control.

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6.4usb_descriptor.c

The audio topology, which is put in USB descriptor, is explained in the AUDIO specification

(/developers/devclass_docs/). The audio topology chose for this

demo is described in the following figure.

Figure 6-3.

Input Terminal N°1

Audio Function Topology from demo

Feature Unit N°2Ouput Terminal N°3

1 channel

USB streamControl volume and muteSpeaker

Input Terminal N°4Feature Unit N°5Ouput Terminal N°6

1 channel

MicrophoneControl volume and muteUSB stream

Software

The USB audio application does not require any PC software. Under Windows

, you can use the

standard recorder “Sound Recorder” to try the microphone feature.

tions

If the speaker is running at 32KHz then recording and playback can’t be running at same time,

due to linited CPU bandwidth when clocked at 8MHz.

d Documents

AVR USB Datasheet (doc 7766)

USB Software Library for AT90USBxxx Microcontrollers (doc 7675)

USB Audio class specification ()

7820A–AVR–11/08

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