package udp // import "github.com/anviod/EtherCAT/internal/link/udp"

Package udp provides a UDP multicast link-layer driver for EtherCAT. 包 udp 提供
EtherCAT 的 UDP 多播链路层驱动。

It implements the ecmd.Framer interface using UDP multicast transport over
golang.org/x/net/ipv4 for multicast group management.

本包使用 golang.org/x/net/ipv4 进行多播组管理， 通过 UDP 多播传输实现 ecmd.Framer 接口。

CONSTANTS

const (
	// EthercatUDPPort is the standard EtherCAT UDP port number.
	EthercatUDPPort = 0x88A4
)

TYPES

type UDPFramer struct {
	// Has unexported fields.
}
    UDPFramer implements ecmd.Framer using UDP multicast transport.

func NewUDPFramer(iface *net.Interface, group net.IP, cycletime time.Duration) (*UDPFramer, error)
    NewUDPFramer creates a new UDP multicast EtherCAT framer.

    It binds a UDP socket to EthercatUDPPort, joins the given multicast group on
    the specified interface, and configures the ipv4.PacketConn for multicast
    send/receive. Loopback is disabled.

func (f *UDPFramer) Close() error
    Close releases the UDP socket and the ipv4.PacketConn.

    Bug fix: the original code called f.Close() recursively inside Close(),
    causing a stack overflow. This version correctly calls f.sock.Close() and
    f.conn.Close() directly.

func (f *UDPFramer) Cycle() (iframes []*ecfr.Frame, err error)
    Cycle sends all queued outgoing frames to the multicast group and reads
    incoming responses.

    It supports cycle stretching: if fewer responses than sent frames are
    received, it will wait up to 10 additional cycle-time periods before giving
    up. Each read operation uses a deadline-based timeout.

func (f *UDPFramer) DebugMessage(m string)
    DebugMessage sends a debug message string to the multicast group on port
    1024. Any error is intentionally ignored.

func (f *UDPFramer) New(maxdatalen int) (*ecfr.Frame, error)
    New creates a new EtherCAT frame wrapped in an Ethernet frame.

    It allocates an Ethernet frame buffer via ecfr.OverlayETHFrame, creates an
    ecfr.Frame in the payload area, and sets the EtherCAT type to 1. The frame
    is queued for the next Cycle() call.