Inter-IC Sound (I²S) Appendix#

This appendix defines Inter-IC Sound (I²S) terminology, expands acronyms, and provides examples and troubleshooting guidance. Use it as a quick reference when developing audio applications on the SiWx917 system-on-chip (SoC) using the WiSeConnect software development kit (SDK).

Glossary#

The glossary defines key terms, acronyms, and concepts related to I²S audio development. Use it to understand clock signals, error conditions, and peripheral components while building or debugging audio systems.

• I²S (Inter-IC Sound): Serial bus interface for digital audio communication.

• BCLK (Bit Clock): Synchronizes the transmission of each data bit.

• FSYNC / LRCLK (Frame Sync / Left-Right Clock): Indicates the start of a frame and distinguishes left/right channels.

• MCLK (Primary Clock): High-frequency reference clock for codecs, typically 256× or 512× the sample rate.

• Primary : Device that generates I²S clock signals.

• Secondary : Device that follows timing generated by the primary.

• DMA / UDMA: Transfers audio data between memory and peripherals without CPU involvement.

• Sample Rate: Number of samples per second (for example, 8 kHz, 16 kHz, 48 kHz).

• Bit Depth: Number of bits per audio sample (for example, 16-bit, 24-bit, 32-bit).

• Channel Configuration: Mono, stereo, or multichannel arrangement.

• Underrun / Overrun: Buffer underflow or overflow caused by processing or timing delays.

• ULP (Ultra-Low-Power): SiWx917 subsystem for energy-efficient audio.

• Power Manager: Manages system power states, peripheral enablement, and RAM retention.

• ADC (Analog-to-Digital Converter): Converts analog audio to digital format.

• DAC (Digital-to-Analog Converter): Converts digital audio to analog.

• FIFO (First-In, First-Out): Buffer that outputs audio data in received order.

• Callback: User-provided function called by the driver on events such as underrun or completion.

• Simplicity Studio: Silicon Labs IDE for embedded development.

• Instance: Hardware peripheral instance (for example, HP I²S or ULP I²S).

• Component: Software module in Simplicity Studio (for example, ULP I²S component).

• PS1 / PS2 / PS4: SiWx917 power states for low-power and high-performance modes.

• DEBUGINIT: Function or macro initializing debug I/O for tracing audio activity.

Acronyms#

Extended Examples#

These examples demonstrate I²S functionality on the SiWx917 platform using the WiSeConnect SDK. Use them as reference implementations when developing your own applications.

• I²S Primary Example — Demonstrates I²S master (controller) mode for transmitting audio.

• I²S Secondary Example — Demonstrates I²S slave (target) mode synchronized to an external master.

• I²S Loopback Example — Tests internal TX/RX path for validation.

• Ultra-Low Power (ULP) I²S Example — Demonstrates low-power streaming in PS2 mode.

FAQ#

Q1: What’s the difference between ULP I²S and HP I²S?#

• ULP I²S: Operates in PS1 and PS2 power states for battery-powered audio applications.

• HP I²S: Operates in PS4 for high-fidelity, high-throughput audio streaming.

• Configure both via the WiSeConnect Power Manager component in Simplicity Studio.

Q2: How do I use I²S in low-power modes (PS2/PS1)?#

• Use the ULP I²S instance for communication in PS2 or PS1.

• Ensure the ULP I²S component is installed in Simplicity Studio.

• Configure power states with the Power Manager.

• Reinitialize after wakeup using sl_si91x_i2s_init().

Q3: What should I do before entering sleep mode?#

• Stop active audio transfers.

• Flush DMA buffers if used.

• Deinitialize the instance using sl_si91x_i2s_deinit().

• Reinitialize after wakeup to restore I²S configuration.

Q4: How do I recover from I²S audio errors or glitches?#

• Use the driver reset sequence:

  sl_si91x_i2s_deinit(I2S_INSTANCE);
  sl_si91x_i2s_init(I2S_INSTANCE, &config);

• Verify clock and data line integrity using a logic analyzer.

• Handle underrun/overrun events via callbacks.

Q5: What are the common error codes returned by I²S APIs?#

Q6: How can I debug I²S audio communication issues?#

• Use a logic analyzer to observe BCLK, FSYNC, and SDIN/SDOUT.

• Check timing alignment and verify left/right channel separation.

• Confirm DMA configuration and FIFO thresholds.

• In Simplicity Studio, use:

  • Peripheral configuration views for I²S pin and clock setup.

  • Power analysis tools to verify domain availability.

  • RTOS-aware debugging for task-level traceability.

Q7: What sample rates and bit depths are supported?#

• Sample Rates: 8 kHz, 16 kHz, 22.05 kHz, 44.1 kHz, 48 kHz, 96 kHz, 192 kHz.

• Bit Depths: 16-bit, 24-bit, 32-bit.

• Channel Configurations: Mono, Stereo, Multi-channel.

Q8: How do I choose the right buffer size for audio applications?#

• Real-time audio: 64–256 samples (low latency).

• Streaming: 512–2048 samples (efficiency).

• Battery-powered: 1024+ samples (minimized wakeups). Balance latency, CPU load, and power usage based on your application.

Q9: What causes audio underruns and overruns?#

• Underruns: Caused by small buffers or insufficient CPU time.

• Overruns: Caused by delayed data reads or processing latency.

• Solutions: Increase buffer size, optimize interrupt handling, use DMA transfers, and tune FIFO thresholds.