EtherCAT.Bus.Datagram (ethercat v0.4.2)

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An EtherCAT datagram struct and wire-format codec (spec §2.2).

Wire layout (all little-endian, LSB first)

Byte  0:     CMD (8 bit)
Byte  1:     IDX (8 bit)
Bytes 2–5:   Address (32 bit, layout depends on CMD)
Bytes 6–7:   Len[10:0] | R[13:11]=0 | C[14] | M[15]
Bytes 8–9:   IRQ (16 bit)
Bytes 10…n:  Data (Len bytes)
Last 2:      WKC (16 bit)

The circulating bit (C) is a slave-side mechanism for detecting frames that loop in a ring after a cable break (spec §3.5). The master always sends C=0; a returned C=1 means the frame circulated (error condition).

Summary

Types

t()

Functions

decode(bin)

Decode a binary into a list of datagrams. Trailing padding bytes (after the last datagram where M=0) are ignored.

encode(datagrams)

Encode a list of datagrams into a contiguous binary.

wire_size(datagram)

Encoded size in bytes: 10-byte header + data + 2-byte WKC.

Types

t()

@type t() :: %EtherCAT.Bus.Datagram{
  address: <<_::32>>,
  circular: boolean(),
  cmd: 0..14,
  data: binary(),
  idx: byte(),
  irq: non_neg_integer(),
  wkc: non_neg_integer()
}

Functions

decode(bin)

@spec decode(binary()) :: {:ok, [t()]} | {:error, atom()}

Decode a binary into a list of datagrams. Trailing padding bytes (after the last datagram where M=0) are ignored.

encode(datagrams)

@spec encode([t()]) :: binary()

Encode a list of datagrams into a contiguous binary.

Sets the M (more) bit on all but the last datagram. The C (circulating) bit is always sent as 0.

wire_size(datagram)

@spec wire_size(t()) :: non_neg_integer()

Encoded size in bytes: 10-byte header + data + 2-byte WKC.