HostLink session state and frame routing

Model status: integration · confirmed; belongs to the cross-processor integration model

Real representation of the session

There is no HostlinkSession class here. A session consists of three explicit structures:

LinkState:Stopped / Waiting / Connected / Handshaking / Ready / Error
Status:state、RX/TX count、last error
SessionRuntime:Status、TX sequence、handshake deadline、status/GPS emit timestamps

Behavior is operated by functions such as reset_session, stop_session, set_link_state, mark_handshake_started, mark_handshake_complete, mark_disconnected and handshake_expired.

Handshake and recovery

stateDiagram-v2
  [*] --> Stopped
  Stopped --> Waiting: reset_session
  Waiting --> Connected: transport connected
  Connected --> Handshaking: mark_handshake_started
  Handshaking --> Ready: mark_handshake_complete
  Handshaking --> Error: handshake_expired
  Ready --> Waiting: mark_disconnected
  Error --> Waiting: reset/retry
  Waiting --> Stopped: stop_session

The external triggering of Connected to Handshaking is the responsibility of the caller; the description of these calling relationships in the figure belongs to Inferred and should be verified through execution flow.

Decision before the frame enters the service

hostlink_frame_router.h definition:

HostlinkCommandId
HostlinkFrameDecisionType
HostlinkFrameDecision

Frame router first generates a decision, and then the service/config/event/app-data codec translates the payload. The responsibility of Transport is byte transfer; the responsibility of Session is link status and sequence number; the responsibility of Router is frame classification. These three cannot be combined into "C6 service".

Periodic output

should_emit_status / mark_status_emitted and should_emit_gps / mark_gps_emitted indicate that status and GPS push each have a throttling status; they are part of the SessionRuntime, not the UI timer.

Still needs to be verified

processing rules for sequence wrap-around and old session responses.
Whether version/capability negotiation is completed in the codec or upper-layer service.
retry ownership after Error.

Drilldown and evidence

LinkState and handshake life cycle
modules/core_hostlink/include/hostlink/hostlink_session.h
modules/core_hostlink/src/hostlink_session.cpp
modules/core_hostlink/include/hostlink/hostlink_frame_router.h

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