Notes on Writing a Simple I2C Driver for Audio Codec

Introduction

• Overview of configuring an audio codec for custom hardware.
• Example design with custom PCB utilizing a STM 3287 microcontroller for DSP tasks.

Audio Codec Details

• Codec Used: Sirus Logic CS 4270
• Features:
  • Stereo input/output
  • Sampling frequency: Up to 192 kHz
  • Bit depth: Up to 24 bits
• Characteristics:
  • Signal-to-noise ratio
  • Total harmonic distortion

Configuration Focus

• Interest in I2C register configuration for the audio codec.
• Use of I2C for controlling codec settings (sampling frequencies, bit depths, volume, gains).

I2S Audio Data Transfer

• I2S Pins:
  • ADC (Analog to Digital Converter) sends data back to DSP.
    • Typically called SDIN or SDTI.
  • DAC (Digital to Analog Converter) sends data from DSP to codec.
    • Typically called SDOUT or SDTO.
• Clocks in I2S:
  • Word Clock (Left/Right Clock): Runs at sampling rate (FS).
  • Bit Clock: Runs at 64 times the sampling frequency.
  • Master Clock: Often at 256 times the sampling frequency.
• Modes:
  • Codec typically runs in Slave mode; DSP in Master mode for clock generation.

Codec Configuration Modes

• Standalone Mode:
  • Hardware configuration using logic levels.
• Software Mode:
  • More flexible, uses I2C interface for configurations.
  • Allows changing settings like sampling rate, clock ratios, bit depth, filters, etc.

Typical Configuration Steps

1. Power Up Board: Ensure power rails are stable.
2. Initialize DSP/Microcontroller: Configure I2S interface for audio data transfer.
3. Set up Codec Configuration: Utilize I2C or SPI for configuration.
4. Adjust Codec Registers: Read and write to codec registers based on datasheet guidelines.
5. Verify Settings: Read back registers to ensure correct configurations.

Data Sheet Familiarization

• Overview: Codec capable of up to 24 bits, 192 kHz sampling rate.
• Pin Descriptions: Software mode and standalone configurations.
• Master/Slave Settings: Decide clock generation based on mode.

Driver Implementation in C

• Driver Functions:
  • Initialization function to set up codec registers.
  • Reset function to toggle reset pin.
  • Abstracted read/write functions for I2C communication.
• Initialization Process:
  1. Perform hardware reset of codec.
  2. Set codec into power down mode.
  3. Configure codec registers based on datasheet.
  4. Loop through registers in reverse order for final configurations.

Example Register Configuration

• Power Control Register: Set bits as per datasheet requirements.
• Mode Control Register: Configure for single speed/slave mode.
• Loop through registers: Write configurations and read back for verification.

Conclusion

• Importance of following datasheet guidelines for codec configuration.
• Encouragement to explore professional drivers for more complex implementations.
• Thanks to PCB Way for support in hardware manufacture.

Additional Resources

• Suggested video link for deeper understanding of I2S setup.
• Acknowledgments for viewers and reminders to like/comment/subscribe.