| EN(4) | Device Drivers Manual (vax) | EN(4) | 
en —
en0 at uba0 csr 161000 vector enrint enxint encollide
The en interface provides access to a 3
    Mb/s Ethernet network. Due to limitations in the hardware, DMA transfers to
    and from the network must take place in the lower 64K bytes of the UNIBUS
    address space, and thus this must be among the first UNIBUS devices enabled
    after boot.
Each of the host's network addresses is specified at boot time
    with an SIOCSIFADDR
    ioctl(2). The station
    address is discovered by probing the on-board Ethernet address register, and
    is used to verify the protocol addresses. No packets will be sent or
    accepted until a network address is supplied.
The interface software implements an exponential backoff algorithm when notified of a collision on the cable. This algorithm uses a 16-bit mask and the VAX-11's interval timer in calculating a series of random backoff values. The algorithm is as follows:
en driver appeared in
  4.2BSD.
The hardware does word at a time DMA without byte swapping. To
    compensate, byte swapping of user data must either be done by the user or by
    the system. A kludge to byte swap only IP packets is provided if the
    ENF_SWABIPS flag is defined in the driver and set at
    boot time with an SIOCSIFFLAGS
    ioctl(2).
| February 5, 2019 | NetBSD 10.0 |