doc: add subsystem C API reference pages with Breathe and modernize root portal

api/components.rst

@@ -0,0 +1,11 @@
+.. _api_components:
+
+Audio Processing Components API
+###############################
+
+SOF includes a rich library of standard audio processing components, covering volume control,
+gain attenuation, channel mixing, IIR/FIR equalization, dynamic range compression (DRC),
+sample rate conversion (SRC/ASRC), sound dose measurement, and acoustic filters.
+
+.. doxygengroup:: audio_components_api
+   :project: SOF Project

api/index.rst

@@ -42,6 +42,19 @@ The Doxygen documentation covers the entire public firmware and host-shared inte
 * **Source Code Graphs & File Browsing**:
   Full source file tree, header include dependency graphs, and function call/caller graphs.
 
+Subsystem C API References
+**************************
+
+.. toctree::
+   :maxdepth: 1
+
+   ipc4
+   modules
+   pipeline
+   components
+   rtos
+   math
+
 Building API Documentation Locally
 **********************************
 

api/ipc4.rst

@@ -0,0 +1,11 @@
+.. _api_ipc4:
+
+IPC4 Host-DSP Protocol API
+##########################
+
+The IPC4 protocol defines the communication contract between the host operating system
+driver and the Sound Open Firmware DSP. It governs pipeline creation, module binding,
+audio gateway configuration, runtime parameter adjustment, and asynchronous telemetry.
+
+.. doxygengroup:: ipc4_api
+   :project: SOF Project

api/math.rst

@@ -0,0 +1,12 @@
+.. _api_math:
+
+DSP Math & Filter Libraries API
+###############################
+
+Digital signal processing routines in SOF provide optimized fixed-point and floating-point
+mathematical routines. These include trigonometric approximations, polynomial functions,
+CORDIC algorithms, Fast Fourier Transforms (FFT), IIR/FIR filter structures, and matrix
+operations.
+
+.. doxygengroup:: dsp_math_api
+   :project: SOF Project

api/modules.rst

@@ -0,0 +1,12 @@
+.. _api_modules:
+
+Loadable Module & LLEXT API
+###########################
+
+Sound Open Firmware supports dynamic, modular audio processing through both built-in
+and dynamically loadable ELF extensions (LLEXT). The module API defines the common
+interface contracts, initialization structures, parameter exchange mechanisms,
+and source/sink endpoint buffers.
+
+.. doxygengroup:: module_api
+   :project: SOF Project

api/pipeline.rst

@@ -0,0 +1,12 @@
+.. _api_pipeline:
+
+Audio Pipeline & Buffer API
+###########################
+
+Audio pipelines in SOF represent directed processing graphs linking audio stream sources,
+processing components, interconnect buffers, and audio sinks. This API governs pipeline
+scheduling domains, thread execution models, circular buffer management, and stream
+state transitions.
+
+.. doxygengroup:: audio_pipeline_api
+   :project: SOF Project

api/rtos.rst

@@ -0,0 +1,12 @@
+.. _api_rtos:
+
+RTOS Abstraction Layer API
+##########################
+
+The RTOS abstraction layer decouples Sound Open Firmware core logic from underlying
+real-time operating system primitives. It standardizes spinlocks, mutexes, task
+scheduling, high-resolution clocks, hardware timers, memory allocation pools,
+and cache coherency operations across supported DSP architectures.
+
+.. doxygengroup:: rtos_api
+   :project: SOF Project

index.rst

@@ -1,20 +1,117 @@
-.. meta::
-   :http-equiv=Refresh: 0; url=introduction/index.html
-
-.. raw:: html
-
-   <script type="text/javascript">
-       window.location.replace("introduction/index.html");
-   </script>
-
 .. _SOF_home:
 
 Sound Open Firmware Documentation
 #################################
 
+Welcome to the **Sound Open Firmware (SOF)** technical documentation portal.
+
+Sound Open Firmware is a permissively licensed, open-source audio Digital Signal Processing (DSP) firmware infrastructure, SDK, and real-time execution framework governed under the **Linux Foundation** and directed by the **SOF Technical Steering Committee (TSC)**.
+
+SOF provides transparent, deterministic, low-latency audio processing infrastructure for modern computing architectures ranging from embedded microcontrollers and IoT devices to multi-core client PCs and servers.
+
+.. figure:: introduction/images/sof-waveform.jpeg
+   :alt: Sound Open Firmware audio DSP processing
+   :align: center
+   :width: 100%
+
+Architecture & Key Capabilities
+*******************************
+
+Sound Open Firmware delivers a unified, cross-platform audio software stack across two foundational deployment paradigms:
+
+* **Host-Based Client Architecture**: Where the DSP operates as an accelerator coupled to a host application processor running **Linux**, **ChromeOS**, **Android**, or **Windows**. The mainline Linux kernel driver subsystem (``sound/soc/sof/``) manages firmware lifecycle, dynamic ALSA topology parsing, and aggressive power gating (D0ix runtime idle, D3 cold suspend), while real-time audio streams exchange through mailbox IPC protocols (IPC4 and IPC3) and host DMA memory windows.
+* **Hostless & Standalone Architecture**: Where SOF executes autonomously on microcontrollers and embedded DSPs (such as the **Espressif ESP32-P4** or **PJRC Teensy 4.1 / i.MX RT1062**) atop the **Zephyr RTOS**. Standalone topologies process audio directly between hardware peripherals (I2S/TDM, SoundWire, PDM microphones, and S/PDIF) without requiring a host OS.
+
+Documentation Pillars & Navigation
+**********************************
+
+Explore the documentation portal by selecting one of the core technical pillars below:
+
 .. raw:: html
 
-   <p>Redirecting to <a href="introduction/index.html">Introduction to the SOF Project</a>...</p>
+   <div style="display: grid; grid-template-columns: repeat(auto-fit, minmax(280px, 1fr)); gap: 1.25rem; margin: 1.5rem 0 2rem 0;">
+
+     <div style="border: 1px solid var(--pst-color-border, #e5e7eb); border-radius: 8px; padding: 1.25rem; background: var(--pst-color-surface, #ffffff); box-shadow: 0 1px 3px rgba(0,0,0,0.05); display: flex; flex-direction: column;">
+       <h4 style="margin-top: 0; color: var(--pst-color-primary, #0a7d91); font-size: 1.15rem; font-weight: 600;">
+         <a href="introduction/index.html" style="text-decoration: none; color: inherit;">Introduction to SOF &rarr;</a>
+       </h4>
+       <p style="font-size: 0.925rem; line-height: 1.45; margin-bottom: 0.75rem; flex-grow: 1;">
+         Learn about the SOF project mission, benefits of audio DSP offloading (power, deterministic latency, vertical stack centralization), licensing, and governance.
+       </p>
+       <a href="introduction/index.html" style="font-size: 0.875rem; font-weight: 600; color: var(--pst-color-primary, #0a7d91);">Read Introduction &raquo;</a>
+     </div>
+
+     <div style="border: 1px solid var(--pst-color-border, #e5e7eb); border-radius: 8px; padding: 1.25rem; background: var(--pst-color-surface, #ffffff); box-shadow: 0 1px 3px rgba(0,0,0,0.05); display: flex; flex-direction: column;">
+       <h4 style="margin-top: 0; color: var(--pst-color-primary, #0a7d91); font-size: 1.15rem; font-weight: 600;">
+         <a href="getting_started/index.html" style="text-decoration: none; color: inherit;">Getting Started &rarr;</a>
+       </h4>
+       <p style="font-size: 0.925rem; line-height: 1.45; margin-bottom: 0.75rem; flex-grow: 1;">
+         Set up your build host, configure the LLVM/Clang Xtensa cross-compiler toolchain, compile firmware images for target platforms, and run simulation in QEMU.
+       </p>
+       <a href="getting_started/index.html" style="font-size: 0.875rem; font-weight: 600; color: var(--pst-color-primary, #0a7d91);">Explore Quickstart &raquo;</a>
+     </div>
+
+     <div style="border: 1px solid var(--pst-color-border, #e5e7eb); border-radius: 8px; padding: 1.25rem; background: var(--pst-color-surface, #ffffff); box-shadow: 0 1px 3px rgba(0,0,0,0.05); display: flex; flex-direction: column;">
+       <h4 style="margin-top: 0; color: var(--pst-color-primary, #0a7d91); font-size: 1.15rem; font-weight: 600;">
+         <a href="architectures/index.html" style="text-decoration: none; color: inherit;">Architecture & System Design &rarr;</a>
+       </h4>
+       <p style="font-size: 0.925rem; line-height: 1.45; margin-bottom: 0.75rem; flex-grow: 1;">
+         Deep dive into firmware architecture: audio pipeline execution graphs (DAGs), lockless ring buffers, Zephyr RTOS abstraction, IPC3/IPC4 protocols, and power management.
+       </p>
+       <a href="architectures/index.html" style="font-size: 0.875rem; font-weight: 600; color: var(--pst-color-primary, #0a7d91);">View Architecture &raquo;</a>
+     </div>
+
+     <div style="border: 1px solid var(--pst-color-border, #e5e7eb); border-radius: 8px; padding: 1.25rem; background: var(--pst-color-surface, #ffffff); box-shadow: 0 1px 3px rgba(0,0,0,0.05); display: flex; flex-direction: column;">
+       <h4 style="margin-top: 0; color: var(--pst-color-primary, #0a7d91); font-size: 1.15rem; font-weight: 600;">
+         <a href="platforms/index.html" style="text-decoration: none; color: inherit;">Supported Platforms Matrix &rarr;</a>
+       </h4>
+       <p style="font-size: 0.925rem; line-height: 1.45; margin-bottom: 0.75rem; flex-grow: 1;">
+         Hardware compatibility specifications across Intel CAVS & ACE (PTL, ARL, MTL, TGL), AMD, NXP i.MX, MediaTek, Espressif ESP32-P4, and PJRC Teensy 4.1.
+       </p>
+       <a href="platforms/index.html" style="font-size: 0.875rem; font-weight: 600; color: var(--pst-color-primary, #0a7d91);">Browse Platforms &raquo;</a>
+     </div>
+
+     <div style="border: 1px solid var(--pst-color-border, #e5e7eb); border-radius: 8px; padding: 1.25rem; background: var(--pst-color-surface, #ffffff); box-shadow: 0 1px 3px rgba(0,0,0,0.05); display: flex; flex-direction: column;">
+       <h4 style="margin-top: 0; color: var(--pst-color-primary, #0a7d91); font-size: 1.15rem; font-weight: 600;">
+         <a href="algos/index.html" style="text-decoration: none; color: inherit;">Audio Algorithms & Components &rarr;</a>
+       </h4>
+       <p style="font-size: 0.925rem; line-height: 1.45; margin-bottom: 0.75rem; flex-grow: 1;">
+         Comprehensive catalog of built-in audio signal processing modules: Volume, Mixer, Parametric EQ (FIR/IIR), DRC, SRC, ASRC, Crossover, DCBlock, and Wake-on-Voice.
+       </p>
+       <a href="algos/index.html" style="font-size: 0.875rem; font-weight: 600; color: var(--pst-color-primary, #0a7d91);">Inspect Algorithms &raquo;</a>
+     </div>
+
+     <div style="border: 1px solid var(--pst-color-border, #e5e7eb); border-radius: 8px; padding: 1.25rem; background: var(--pst-color-surface, #ffffff); box-shadow: 0 1px 3px rgba(0,0,0,0.05); display: flex; flex-direction: column;">
+       <h4 style="margin-top: 0; color: var(--pst-color-primary, #0a7d91); font-size: 1.15rem; font-weight: 600;">
+         <a href="developer_guides/index.html" style="text-decoration: none; color: inherit;">Developer Guides & Runbooks &rarr;</a>
+       </h4>
+       <p style="font-size: 0.925rem; line-height: 1.45; margin-bottom: 0.75rem; flex-grow: 1;">
+         Step-by-step developer runbooks: ALSA Topology 2 creation, UCM2 configuration and debugging, LLEXT dynamic module integration, CMake workflows, and real-time DSP probes.
+       </p>
+       <a href="developer_guides/index.html" style="font-size: 0.875rem; font-weight: 600; color: var(--pst-color-primary, #0a7d91);">Read Guides &raquo;</a>
+     </div>
+
+     <div style="border: 1px solid var(--pst-color-border, #e5e7eb); border-radius: 8px; padding: 1.25rem; background: var(--pst-color-surface, #ffffff); box-shadow: 0 1px 3px rgba(0,0,0,0.05); display: flex; flex-direction: column;">
+       <h4 style="margin-top: 0; color: var(--pst-color-primary, #0a7d91); font-size: 1.15rem; font-weight: 600;">
+         <a href="api/index.html" style="text-decoration: none; color: inherit;">C API & Firmware Reference &rarr;</a>
+       </h4>
+       <p style="font-size: 0.925rem; line-height: 1.45; margin-bottom: 0.75rem; flex-grow: 1;">
+         Interactive Doxygen API documentation and Sphinx Breathe subsystem reference for IPC4, LLEXT modules, pipeline scheduling, audio components, RTOS abstraction, and DSP math.
+       </p>
+       <a href="api/index.html" style="font-size: 0.875rem; font-weight: 600; color: var(--pst-color-primary, #0a7d91);">Explore C API &raquo;</a>
+     </div>
+
+     <div style="border: 1px solid var(--pst-color-border, #e5e7eb); border-radius: 8px; padding: 1.25rem; background: var(--pst-color-surface, #ffffff); box-shadow: 0 1px 3px rgba(0,0,0,0.05); display: flex; flex-direction: column;">
+       <h4 style="margin-top: 0; color: var(--pst-color-primary, #0a7d91); font-size: 1.15rem; font-weight: 600;">
+         <a href="contribute/index.html" style="text-decoration: none; color: inherit;">Community & Contributing &rarr;</a>
+       </h4>
+       <p style="font-size: 0.925rem; line-height: 1.45; margin-bottom: 0.75rem; flex-grow: 1;">
+         Join the SOF open-source community: contributor guidelines, Git patch submission rules, TSC meeting minutes, releases, and frequently asked questions.
+       </p>
+       <a href="contribute/index.html" style="font-size: 0.875rem; font-weight: 600; color: var(--pst-color-primary, #0a7d91);">Contribute &raquo;</a>
+     </div>
+
+   </div>
 
 .. toctree::
    :hidden:
@@ -32,4 +129,3 @@ Sound Open Firmware Documentation
    api/index.rst
    presentations/index.rst
    faq/index.rst
-