4.1cBSD/usr/man/man4/en.4v

.TH EN 4V "26 March 1982"
.UC 4
.SH NAME
en \- Xerox 3 Mb/s Ethernet interface
.SH SYNOPSIS
.B "device en0 at uba0 csr 161000 flags 0x4e000226 vector enrint enxint encollide"
.SH DESCRIPTION
The
.I en
interface provides access to a 3 Mb/s Ethernet network.
In configuring, the flags value is used to define the 
network to which the interface is attached.
The host's address
is discovered at boot time by probing the Ethernet address
register.  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.
.PP
The interface software implements an exponential backoff algorithm
when notified of a collision on the cable.  This algorithm utilizes
a 16-bit mask and the VAX-11's interval timer in calculating a series
of random backoff values.  The algorithm is as follows:
.TP
1.
Initialize the mask to be all 1's.
.TP
2.
If the mask is zero, 16 retries have been made and we give
up.
.TP
3.
Shift the mask left one bit and formulate a backoff by
masking the interval timer with the mask (this is actually
the two's complement of the value).
.TP
4.
Use the value calculated in step 3 to delay before retransmitting
the packet.
.PP
The interface handles both Internet and PUP protocol families,
with the interface address maintained in Internet format.
PUP addresses are converted to Internet addresses by subsituting
PUP network and host values for Internet network and imp values,
and setting the Internet host number to zero.
.SH DIAGNOSTICS
.BR "en%d: output error" .
The hardware indicated an error on
the previous transmission.
.PP
.BR "en%d: send error" .
After 16 retransmissions using the
exponential backoff algorithm described above, the packet
was dropped.
.PP
.BR "en%d: input error" .
The hardware indicated an error
in reading a packet off the cable.
.PP
.BR "en%d: can't handle af%d" .
The interface was handed
a message with addresses formatted in an unsuitable address
family; the packet was dropped.
.SH SEE ALSO
intro(4N), inet(4F)
.SH BUGS
The device has insufficient buffering to handle back to
back packets.  This makes use in a production environment
painful.