ec.4

<B>Digital的Unix操作系统VAX 4.2源码</B>

.\" SCCSID: @(#)ec.4	8.1	9/11/90
.TH ec 4 VAX "" Unsupported
.SH Name
ec \- 3Com 10 Mb/s Ethernet interface
.SH Syntax
.B "device ec0 at uba0 csr 0161000 vector ecrint eccollide ecxint"
.SH Description
The
.PN ec
interface provides access to a 10 Mb/s Ethernet network through
a 3com controller.
.PP
The hardware has 32 kilobytes of dual-ported memory on the UNIBUS. 
This memory
is used for internal buffering by the board, and the interface code reads
the buffer contents directly through the UNIBUS.
.PP
The host's Internet address is specified at boot time with an SIOCSIFADDR
ioctl.  The
.PN ec
interface employs the address resolution protocol described in
.MS arp 4p
to dynamically map between Internet and Ethernet addresses on the local
network.
.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 5
1.
Initialize the mask to be all 1's.
.TP 5
2.
If the mask is zero, 16 retries have been made and we give
up.
.TP 5
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 5
4.
Use the value calculated in step 3 to delay before retransmitting
the packet.  The delay is done in a software busy loop.
.PP
The interface normally tries to use a ``trailer'' encapsulation
to minimize copying data on input and output.  This may be
disabled, on a per-interface basis, by setting the IFF_NOTRAILERS
flag with an SIOCSIFFLAGS ioctl.
.SH Diagnostics
.BR "ec%d: send error" .
.br
After 16 retransmissions using the
exponential backoff algorithm described above, the packet
was dropped.
.PP
.BR "ec%d: input error (offset=%d)" .
.br
The hardware indicated an error
in reading a packet off the cable or an illegally sized packet.
The buffer offset value is printed for debugging purposes.
.PP
.BR "ec%d: can't handle af%d" .
.br
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), arp(4p)