116 lines
2.5 KiB
Markdown
116 lines
2.5 KiB
Markdown
# ADR-002: SPI Control Architecture
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- Status: Accepted
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- Date: 2026-08-01
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- Decision Type: Hardware Architecture
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## Context
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HubAudio integrates multiple programmable devices requiring configuration,
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control and firmware management.
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The main devices involved are:
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- ESP32-S3 system controller
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- ADAU1467 audio processor
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- Si4684 radio receiver
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A clear separation between system control and internal device management is
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required.
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The SPI interface is used exclusively as a control interface and not as an
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audio transport interface.
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## Decision
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The SPI architecture is divided into independent functional domains.
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The ESP32-S3 operates as the master of the system control SPI bus.
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The ADAU1467 and Si4684 expose SPI slave interfaces for external
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configuration and control.
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The internal management of each device remains under the responsibility of
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the device itself.
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## Architecture
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System control SPI domain:
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ESP32-S3
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SPI MASTER
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+---------+---------+
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ADAU1467 Si4684
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SPI SLAVE SPI SLAVE
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## ADAU1467 Configuration Domain
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The ADAU1467 manages its own external configuration memory through its
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internal SPI master interface.
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ADAU1467
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SPI MASTER
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25AA1024
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DSP Program / Configuration Memory
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The ESP32-S3 controls the ADAU1467 through the external SPI interface but
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does not directly access the DSP configuration memory during normal
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operation.
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## Si4684 Firmware Domain
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The Si4684 firmware loading and configuration process is managed through
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commands exchanged on the external SPI control interface.
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ESP32-S3
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SPI MASTER
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Si4684
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Internal Firmware Loader
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Internal RAM
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The ESP32-S3 controls the initialization process but does not directly access
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the internal operational memory of the Si4684.
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## Consequences
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### Positive
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- Clear ownership of every SPI interface
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- No bus contention between devices
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- Reduced electrical loading
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- Independent device initialization
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- Easier debugging and validation
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### Negative
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- Multiple control interfaces are required
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- Firmware update procedures must coordinate different device domains
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## Rationale
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The ESP32-S3 supervises the complete HubAudio system but does not replace the
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internal controllers of specialized devices.
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Each component remains responsible for its own functional domain.
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The control plane and the audio plane remain architecturally separated. |