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 9.4 |