AirPlay.V2.PtpBmca (AirPlay v0.4.2)

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AirPlay 2 gPTP BMCA-yield worker.

This follows the audible airplay2-rs/HomePod flow:

  • bind PTP event/general sockets on 319/320
  • send Mac-style Sync + Announce + Signaling with priority 250
  • yield to the receiver's better clock
  • act as a PTP slave and derive the receiver-clock offset

HomePods never answer our Delay_Req, so the classic two-way exchange cannot complete. Instead the offset is taken one-way from each Sync/Follow_Up pair (t1 - t2), which is what lets receiver_time_ns/2 track the receiver's own PTP clock — a HomePod's clock is its uptime, nowhere near the host's wall clock, so an un-converged (zero) offset stamps audio decades into the receiver's future and it plays nothing.

Summary

Types

t()

Functions

offset(ptp_bmca)

Return the last measured clock offset.

receiver_time_ns(session, local_ns \\ now_ns())

Convert local wall-clock time to the receiver's PTP timeline.

start_link(host, opts \\ [])

Start the BMCA-yield worker for a receiver host.

stop(ptp_bmca)

Stop a BMCA worker.

Types

t()

@type t() :: %AirPlay.V2.PtpBmca{clock_id: binary() | nil, pid: pid(), state: pid()}

Functions

offset(ptp_bmca)

@spec offset(t()) :: map()

Return the last measured clock offset.

receiver_time_ns(session, local_ns \\ now_ns())

@spec receiver_time_ns(t(), integer()) :: non_neg_integer()

Convert local wall-clock time to the receiver's PTP timeline.

start_link(host, opts \\ [])

@spec start_link(
  String.t() | :inet.ip_address(),
  keyword()
) :: {:ok, t()} | {:error, term()}

Start the BMCA-yield worker for a receiver host.

stop(ptp_bmca)

@spec stop(t()) :: :ok

Stop a BMCA worker.