Embedded SoPC Design with Nios II Processor and Verilog Examples

CHAPTER 19

AUDIO CODEC CONTROLLER

An audio codec device can digitize an analog audio signal and convert the digitized signal back to analog format. The DE1 board contains a Wolfson WM8731 codec device. In this chapter, we discuss the interface circuit for WM8731 and the software driver. The hardware portion includes an I²C controller for device configuration and a data access control circuit to process incoming and outgoing audio data streams. The software portion includes the driver routines to send an I²C packet, set up WM8731, and to transmit and receive audio data as well as basic routines to process an audio file in an uncompressed WAV format.

19.1 INTRODUCTION

Audio signals are in a continuous analog format. To take advantage of the capability of a digital system, an analog signal must be converted to discrete digital numbers. The digitized data then can be stored and processed by a digital system. During playback, the data are converted back to an analog signal. A specific device, known as an audio codec, is designed for this purpose. The DE1 board contains a codec device, WM8731, from Wolfson Microelectronics.

19.1.1 Overview of codec

An audio codec device converts (i.e., code) analog signals into digital data and converts (i.e., decode) the data back to analog signals. It is essentially an interface from and to the analog domain. A codec contains an ADC (analog-to-digital converter) and a DAC (digital-to-analog converter). An ADC converts an input analog voltage to a discrete ...