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IPC3 Architecture

This directory houses the Version 3 Inter-Processor Communication handling components. IPC3 is the older, legacy framework structure used extensively across initial Sound Open Firmware releases before the transition to IPC4 compound pipeline commands.

Overview

The IPC3 architecture treats streaming, DAI configurations, and pipeline management as distinct scalar events. Messages arrive containing a specific sof_ipc_cmd_hdr denoting the "Global Message Type" (e.g., Stream, DAI, Trace, PM) and the targeted command within that type.

Command Structure and Routing

Every message received is placed into an Rx buffer and initially routed to ipc_cmd(). Based on the cmd inside the sof_ipc_cmd_hdr, it delegates to one of the handler subsystems:

  • ipc_glb_stream_message: Stream/Pipeline configuration and states
  • ipc_glb_dai_message: DAI parameters and formats
  • ipc_glb_pm_message: Power Management operations
graph TD
    Mailbox[IPC Mailbox Interrupt] --> Valid[mailbox_validate]
    Valid --> Disp[IPC Core Dispatcher]

    Disp -->|Global Type 1| StreamMsg[ipc_glb_stream_message]
    Disp -->|Global Type 2| DAIMsg[ipc_glb_dai_message]
    Disp -->|Global Type 3| PMMsg[ipc_glb_pm_message]
    Disp -->|Global Type ...| TraceMsg[ipc_glb_trace_message]

    subgraph Stream Commands
        StreamMsg --> StreamAlloc[ipc_stream_pcm_params]
        StreamMsg --> StreamTrig[ipc_stream_trigger]
        StreamMsg --> StreamFree[ipc_stream_pcm_free]
        StreamMsg --> StreamPos[ipc_stream_position]
    end

    subgraph DAI Commands
        DAIMsg --> DAIConf[ipc_msg_dai_config]
    end

    subgraph PM Commands
        PMMsg --> PMCore[ipc_pm_core_enable]
        PMMsg --> PMContext[ipc_pm_context_save / restore]
    end
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Processing Flows

Stream Triggering (ipc_stream_trigger)

Triggering is strictly hierarchical via IPC3. It expects pipelines built and components fully parsed prior to active streaming commands.

  1. Validation: The IPC fetches the host component ID.
  2. Device Lookup: It searches the components list (ipc_get_comp_dev) for the PCM device matching the pipeline.
  3. Execution: If valid, the pipeline graph is crawled recursively and its state altered via pipeline_trigger.
sequenceDiagram
    participant Host
    participant IPC3 as IPC3 Handler (ipc_stream_trigger)
    participant Pipe as Pipeline Framework
    participant Comp as Connected Component

    Host->>IPC3: Send SOF_IPC_STREAM_TRIG_START
    activate IPC3
    IPC3->>IPC3: ipc_get_comp_dev(stream_id)
    IPC3->>Pipe: pipeline_trigger(COMP_TRIGGER_START)
    activate Pipe
    Pipe->>Comp: pipeline_for_each_comp(COMP_TRIGGER_START)
    Comp-->>Pipe: Success (Component ACTIVE)
    Pipe-->>IPC3: Return Status
    deactivate Pipe

    alt If Success
        IPC3-->>Host: Acknowledge Success Header
    else If Error
        IPC3-->>Host: Acknowledge Error Header (EINVAL / EIO)
    end
    deactivate IPC3
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DAI Configuration (ipc_msg_dai_config)

DAI (Digital Audio Interface) configuration involves setting up physical I2S, ALH, SSP, or HDA parameters.

  1. Format Unpacking: Converts the sof_ipc_dai_config payload sent from the ALSA driver into an internal DSP structure ipc_config_dai.
  2. Device Selection: Identifies the exact DAI interface and finds its tracking device ID via dai_get.
  3. Hardware Config: Applies the unpacked settings directly to the hardware via the specific DAI driver's set_config function.
sequenceDiagram
    participant Host
    participant IPC3 as IPC3 Handler (ipc_msg_dai_config)
    participant DAIDev as DAI Framework (dai_get)
    participant HWDriver as HW Specific Driver (e.g. SSP)

    Host->>IPC3: Send SOF_IPC_DAI_CONFIG (e.g., SSP1, I2S Format)
    activate IPC3

    IPC3->>IPC3: build_dai_config()
    IPC3->>DAIDev: dai_get(type, index)
    DAIDev-->>IPC3: pointer to dai instance

    IPC3->>HWDriver: dai_set_config()
    activate HWDriver
    HWDriver-->>HWDriver: configures registers
    HWDriver-->>IPC3: hardware configured
    deactivate HWDriver

    IPC3-->>Host: Acknowledged Setting
    deactivate IPC3
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Mailbox and Validation (mailbox_validate)

All commands passing through this layer enforce rigid payload boundaries. mailbox_validate() reads the first word directly from the mailbox memory, identifying the command type before parsing parameters out of shared RAM to prevent host/DSP mismatches from cascading.