[zxzxwu]

Implement the non-enhanced Setup/Accept/Reject Synchronous Connection commands, so that SCO and eSCO links can be set up with controllers that do not implement the enhanced commands, and let the SCO examples fall back to them.

Problem

Bumble had the non-enhanced Accept and Reject Synchronous Connection commands (0x0429, 0x042A) and the events that go with them, but not the non-enhanced Setup Synchronous Connection command (0x0428), so a host could not create a SCO or eSCO link on a controller that only implements the non-enhanced commands. Realtek RTL8761 based dongles (e.g. ASUS BT600) are such controllers: they report neither 0x043D nor 0x043E.

The SCO examples sent the enhanced commands unconditionally (one of them had a hand-rolled fallback with its own voice setting mapping), and the emulated controller only implemented the enhanced commands, so that path could not be tested without hardware.

Fix

• bumble/hci.py: add the missing HCI_Setup_Synchronous_Connection_Command (0x0428), with a PacketType flag and SCO_PACKET_TYPES / ESCO_PACKET_TYPES masks, and VoiceSetting.codec_id(), which maps the Air_Coding_Format of a voice setting to the air mode (codec ID) of the Synchronous Connection Complete event (the two use different numbering).
• bumble/controller.py: implement the non-enhanced Setup, Accept and Reject commands. The non-enhanced setup command does not say whether a SCO or an eSCO link is wanted: make it an eSCO link if any of the eSCO packet types is allowed, and a SCO link otherwise. Also report the air mode of the link in the Synchronous Connection Complete event (from the voice setting for the non-enhanced commands, from the coding format for the enhanced ones) instead of always reporting 0 — the USB transport uses that air mode to select the isochronous alternate setting (see Fix SCO over USB: align packets to the alternate setting, select it per SCO link #1011).
• bumble/hfp.py: add EscoParameters.as_legacy_dict(), which reduces codec parameters to the parameters of the non-enhanced commands (the air coding format is taken from the transmit coding format: mSBC and LC3 are coded by the host, so they go over the air as transparent data; the rest of the coding format is reduced to the sample size, format and bit position of the PCM data on HCI), and setup_synchronous_connection_command() / accept_synchronous_connection_request_command(), which return the enhanced command when the controller supports it and the non-enhanced one otherwise.
• examples/: run_esco_connection.py, run_hfp_gateway.py and run_hfp_handsfree.py use those builders, so they work with both kinds of controller (and the hand-rolled fallback in run_hfp_handsfree.py goes away).

Testing

• Unit tests: the non-enhanced Setup command round-trips (SCO and eSCO packet types); VoiceSetting.codec_id(); the legacy parameter mapping (CVSD, mSBC, 8-bit PCM, sign and magnitude); a full eSCO setup and a full SCO setup over the emulated controller with the non-enhanced commands, a setup that the peer rejects, and the existing enhanced setups, all asserting the link type and the air mode. Full suite: 1045 passed, 2 skipped. black -S --check, ruff check, mypy and pylint -E are clean.

• Realtek (2x ASUS BT600, 0b05:1d70, RTL8761CU), which only implements the non-enhanced commands: examples/run_esco_connection.py between the two dongles picks the non-enhanced commands automatically, and both sides report an eSCO link with CVSD air mode and 60-byte packets:

  HOST -> CONTROLLER: HCI_SETUP_SYNCHRONOUS_CONNECTION_COMMAND
  HOST -> CONTROLLER: HCI_ACCEPT_SYNCHRONOUS_CONNECTION_REQUEST_COMMAND
  ### SCO CONNECTION: [0x0002] …
    link_type: ESCO
    air_mode:  CVSD
    rx_packet_length: 60   tx_packet_length: 60
  

  Requesting HV3 only (Core spec SCO packet types) still yields an eSCO link on this controller (link_type 0x02, tx_packet_length 540), which looks like a firmware quirk: bumble reports what the controller reports.

Notes

• This does not change the enhanced commands or the behaviour of controllers that implement them; the builders only choose the command that the controller advertises.
• SCO data on the dongles above still needs the alternate setting handling of Fix SCO over USB: align packets to the alternate setting, select it per SCO link #1011 (the link itself is set up with or without it).
• The non-enhanced commands have no way to describe the codec, so the fallback cannot express everything the enhanced commands can: as_legacy_dict() documents what is kept and what is not.