# `EtherCAT.Transport.BPF`
[🔗](https://github.com/tallakt/yaethercat/blob/v0.1.0/lib/ethercat/transport/bpf.ex#L1)

Raw Ethernet on macOS, through a BPF device (`/dev/bpfN`).

macOS has no packet sockets, and a BPF device needs `ioctl` calls that the BEAM can't make. So a
small C program, `priv/bpf/ethercat_bpf.c`, opens the device and passes frames to and fro as an
Erlang port: a process of its own, so that a crash there closes the port and leaves the BEAM
running. It is built with `cc` when yaethercat is compiled on macOS, and nowhere else. It receives
frames of EtherType 0x88A4 only, and none this machine sent.

It needs read and write access to `/dev/bpf*`: root, or membership of the group `access_bpf`, which
Wireshark's ChmodBPF sets up.

Options of `open/1`:

  * `interface:`, required, as `"en7"`

# `program`

```elixir
@spec program() :: Path.t()
```

The path of the port program, built when yaethercat is compiled on macOS.

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*Consult [api-reference.md](api-reference.md) for complete listing*