ECE 354 Spring 2006

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ECE 354Spring 2006

• Lab 5 Using the WM8731
• Developed by Ben Doherty

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In this lab, you will

• Use a simple solid-state, flash memory file
  system (ZipFS)
• Operate the WM8731 audio CODEC chip
• Write both Verilog modules and C code
• Use custom Verilog modules along side the NIOS
  core
• Use C to interact with external Verilog modules

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System Overview
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Overview

• Create a design that can play tones using sine
  waves and the math.h library
• Use the switches to change the frequencies
• Press a button to play tone
• Volume control using buttons
• Interface with the WM8731 Audio CODEC
  (Encoder/Decoder)
• MPU interface
• Audio Interface

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Using the WM8731 Audio CODEC

• Configured via Software Control Interface
• MPU Interface
• There is no SOPC component to drive the
  interface, so it must be done in software (using
  PIO,) or with a custom Verilog module
• Audio samples are sent via the Audio Interface
• No SOPC component for this either
• USB/Normal mode master clock (AUD_XCLK, from
  which AUD_BCLK is generated)
• USB mode must have a FIXED AUD_XCLK of 12MHz,
  which can be easily obtained from a PLL in the
  SOPC system
• Normal mode requires AUD_XCLK clocks of either
  12.288MHz (8kHz, 32kHz, 48kHz, 96kHz) or
  11.2896MHz (44.1kHz, 88.2kHz)

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Audio Stream Format

• Serial bit stream, I2C format
• Format is software configurable, but I2C is
  default (and has the easiest timing)
• Sampling data is interleaved, selected by DACLRCK
• AUD_BCLK and AUD_DACLRCK is generated by the
  CODEC (in MASTER mode,) or by your system (CODEC
  in SLAVE mode)
• Period of AUD_DACLRCK is 1/sampling_rate
• Period of AUD_BCLK is fixed. Try to get as close
  as possible to one of 11.2896MHz, 12.288MHz,
  16.9344MHz or 18.432MHz(Normal mode) and
  12MHz(USB mode) Sampling rate is derived from
  these clocks
• Use a PLL!

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Audio Stream Format (cont.)

• Your Audio Interface module should
• Convert N-bit wide sample from PIO into I2C
  serial format
• The value of N is up to you 32 is probably best
  (two 16-bit wide channels)
• The WM8731 always plays 16-bit samples, padding
  or truncating differing sample widths
• Either generate AUD_BCLK and AUD_DACLRCK (CODEC
  in SLAVE mode,) or accept AUD_BCLK and
  AUD_DACLRCK from CODEC (CODEC in MASTER mode)

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Audio Stream Considerations

• How do you know the module is ready for a new
  sample?
• AUD_DACLRCK accepts on sample per period
• How should your module generate the proper
  clocks?
• Generating and multiplexing multiple clocks is a
  very useful Verilog technique
• You wont always be dividing by factors of 2!!
• Thus you cant just pull a clock from some bit in
  a counter
• It may be possible to write the audio driver in
  software but it needs to have very precise timing
  which is not guaranteed!

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A Bigger Picture (Audio Interface)

BCLK DACLRCK DACDAT
BCLK DACLRCK DACDAT
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WM8731 MPU Interface

• The WM8731 is a WRITE-ONLY device, any requests
  to read are ignored
• Device is configured by writing data to registers
• Transfer initiated by pulling MPU_DATA low while
  MPU_CLK is high
• 3-byte transfers
• Byte 1 ADDR7..0
• ADDR7..0 is DEVICE ADDRESS, which is ALWAYS
  0x34
• Last bit is R/W bit, which is always 0 (write,)
  since WM8731 is write-only
• Byte 2 REG6..0,DATA8
• REG6..0 is 7-bit register address, DATA8 is
  MSB of 9-bit DATA
• Byte 3 DATA7..0
• Lower 8 bits of 9-bit DATA

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WARNING USERS MANUAL IS WRONG!!

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WM8731 MPU Interface (cont.)

• MPU_DATA is driven low by the CODEC between bytes
  as confirmation
• This will require a bi-directional pin
• Verilog Hint
• wire MPU_DATA SDIN ? 1'bz 0
• Pin is wired to VCC via a pull-up resistor on the
  DE2 What does setting MPU_DATA to Z do?
• The SPI-2-MPU module should convert 2 one-byte
  SPI messages into the MPU format
• Store and forward Register/Data values
• First byte is always fixed!
• The SPI HAL cant support SPI transfers greater
  than 8 bits, so two messages must be sent

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WM8731 Configuration

• Use wm8731.h from website for register name
  definitions
• What needs to be configured?
• Reset device Write 0x00 to AUDIO_RESET
• Power up device AUDIO_POWER_DOWN_CTL
• Activate interfaces AUDIO_ACTIVE_CTL
• Disable Line IN -gt Line OUT bypass, select DAC on
  Line OUT AUDIO_ANALOG_PATH_CTL
• Disable DAC soft mute AUDIO_DIGITAL_PATH_CTL
• Turn on MASTER mode AUDIO_INTERFACE_FMT
• Headphone Out (i.e., line out,) volume
  AUDIO_LEFT,RIGHT_HP_OUT
• Can be set simultaneously by setting LRHPBOTH bit

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Tips for Starting

• MPU interface first
• Need to be able to control the CODEC before you
  can test the audio stream
• Make it easy on yourself
• Generate as few signals as you can
• Mono might be easier at first
• Use sufficient ACKs
• One way to know your verilog module works is if
  it ACKs to you on a PIO
• Use GPIO pins
• Monitor lines via these pins then use go logic to
  trace them
• Dont try for the wav player until you can play
  sine waves
• Having a file system doesnt do much good if you
  cant play it

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Optional - Flash File System

• Requires CFI Flash and Avalon Tri-State bridge
  SOPC Builder components
• Simple file system based on uncompressed ZIP
  files
• Allows for easy access to files using ANSI C file
  routines
• FILE wav fopen(/mnt/zipfs/foobar.wav, r)

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Optional - Setting up ZipFS

• Create an UNCOMPRESSED .zip file from the set of
  files of your choice
• In the file explorer, select your files/folders,
  click on Add to Zip
• Specify filename
• Set compression level to None
• Move .zip file to the system library folder of
  your Nios II IDE project. One way you can do
  this
• Right-click on the _syslib top level folder of
  your project
• Select Import
• Select File System and click Next
• Browse to containing folder of .zip file
• Select .zip file from list in right hand pane
• Click Finish

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Optional - Setting up Zip FS (cont.)

• Enable the Zip FS in the System Library
• Open System Library Properties (In Properties
  dialog)
• Click on Software Components
• Choose Altera Zip Read-Only File System
• Select Add this software component
• Specify zip file and mount point
• Mount point is root of files, leave as
  /mnt/rozipfs or /mnt/zipfs if you choose
• Select OK, go back to main screen

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Optional - Writing Zip FS to Flash

• Make sure your zip file is UNCOMPRESSED, and is
  in the system library directory
• Go to Tools-gtFlash Programmer
• Select ONLY Program a file into flash memory
• Select your zip file
• Click Program Flash
• Files can now be accessed using ANSI C fopen()
  and fread() functions

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Optional - Parsing .wav files

• Wav files are a modified version of the RIFF
  standard
• First 4 bytes are RIFF,
• Next 4 bytes are length of file
• Next 4 bytes are WAVE
• File divided into chunks
• Chunk Header 4 byte name, 4 byte length
• fmt (notice space) defines format of wav file
• Usually, but not required to be first chunk
• See wave.h for relevant structures
• data chunk contains audio data

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Optional - Parsing .wav files (cont.)

• Algorithm
• Verify RIFF file header denotes WAVE file
• Read in Chunk Header
• fread(header, 1, sizeof(struct chunk_head),
  wav)
• Check if fmt chunk
• if(strncmp(header.ChunkID, fmt , 4) 0)
• Read in format chunk structure
• struct fmt_chunk fmt
• fread(fmt, 1, sizeof(struct fmt_chunk), wav)
• Determine sampling rate, number of channels and
  sample width. Calculate sample frame size and
  allocate memory for sample frame buffer
  (malloc())
• Read chunks until data chunk found (Usually
  next)
• Read in sample frames and feed to CODEC
• CODEC requires stereo input if only one channel
  in file, duplicate left and right channels

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Experiments

• The WM8731 can not play all the sampling rates
  you are likely to find in .wav files from the
  internet (Like 11.25kHz)
• What happens if you play an audio stream at a
  greater sampling rate?
• What about at a lesser sampling rate?
• Sample resolutions also affect the sound of your
  files
• How does 8-bit sound differ from 16-bit sound?
• Gotcha Bit clock may need to be inverted for
  some sample widths (BCLKINV ON for 8-bit, BCLKINV
  OFF for 16-bit)

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Optional - Caveats

• The Avalon bus used on the NIOS II is relatively
  slow, and its certainly not fast or wide enough
  to play a stream at a sampling rate over 8kHz
• Ways around this include
• Creating your own SOPC component
• Creating a separate component to pipe the data
  directly from the Flash memory unit
• Therefore, your design must be able to play at
  least 8KHz audio streams
• Bonus points if you can get higher sampling rates
  to play correctly!
• UI is unimportant, but a sleek interface will win
  bonus points
• Asynchronous volume control is essential
• File selection using LCD screen?
• Flashing lights? Play time elapsed indicator??
• Be creative! This board has a lot of options.

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References

• Wolfson Micro WM8731 Audio CODEC
  Datasheethttp//www.wolfsonmicro.com/uploads/docu
  ments/en/WM8731.pdf
• Nios II Software Developers Handbookhttp//www.im
  it.kth.se/courses/2B1448/docs/n2sw_nii5v2.pdf
• Nios II Peripherals and Interfaceshttp//www.alte
  ra.com/products/ip/processors/nios2/features/ni2-p
  eripherals.html
• Wave file formathttp//www.borg.com/jglatt/tech/
  wave.htm
• Newlib LibC Referencehttp//vmlinux.org/crash/mir
  ror/www.objsw.com/docs/libc_toc.html
• Terasic DE2 Discussion Forumhttp//www.terasic.co
  m.tw/cgi-bin/page/forum.pl?LanguageEnglishNo1