108 lines
2.4 KiB
Markdown
108 lines
2.4 KiB
Markdown
# ADR-003: I2S Audio Routing Architecture
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- Status: Accepted
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- Date: 2026-08-01
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- Decision Type: Audio Architecture
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## Context
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HubAudio integrates multiple digital audio sources and destinations:
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Sources:
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- System Controller streaming subsystem
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- Radio Receiver radio receiver
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- Bluetooth receiver
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- Optical digital input
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Destinations:
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- Analog audio output through CODEC/DAC
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- Bluetooth transmission
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- Optical digital output
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A deterministic and scalable digital audio routing architecture is required.
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## Decision
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The Audio Processor is the central routing element of the Audio Domain.
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Each major audio device is assigned to a dedicated serial audio interface.
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The preferred architecture is:
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One audio device = One dedicated I2S interface
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The Audio Processor operates as the audio timing reference.
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External audio devices operate as I2S slaves whenever supported.
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## Audio Input Allocation
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| Audio Processor Port | Device | Function |
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|---|---|---|
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| SDATA_IN0 | System Controller | Network audio stream |
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| SDATA_IN1 | Radio Receiver | Radio audio |
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| SDATA_IN2 | DECODEC | Optical digital input |
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| SDATA_IN3 | Bluetooth RX | Wireless audio input |
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System Controller --------
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Radio Receiver ---------
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DECODEC ----------+---- Audio Processor
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BT RX ---------/
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## Audio Output Allocation
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| Audio Processor Port | Device | Function |
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|---|---|---|
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| SDATA_OUT0 | CODEC/DAC | Analog audio output |
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| SDATA_OUT1 | Bluetooth TX | Wireless audio output |
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| SDATA_OUT2 | ENCODEC | Optical digital output |
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| SDATA_OUT3 | Reserved | Future expansion |
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Audio Processor
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+------------+------------+
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CODEC BTTX ENCODEC
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## Clocking
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The Audio Processor provides the master audio timing reference.
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The audio clock domain consists of:
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- MCLK
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- BCLK
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- LRCLK
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All connected audio peripherals must operate synchronized to this clock
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domain.
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## Consequences
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### Positive
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- Deterministic audio timing
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- Simple routing model
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- Independent audio channels
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- Easier debugging
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- Future expansion capability
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### Negative
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- Higher pin usage
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- More PCB routing resources required
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- Peripheral selection must consider I2S slave capability
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## Rationale
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HubAudio prioritizes signal integrity, maintainability and deterministic
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audio behavior over maximum bus utilization.
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The Audio Processor acts as the central audio router of the system. |