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.\"     from: @(#)ace.4	6.5 (Berkeley) 3/27/91
.\"	$Id: ace.4,v 1.2 1993/08/01 07:36:56 mycroft Exp $
.\"
.Dd March 27, 1991
.Dt ACE 4 tahoe
.Os BSD 4.2
.Sh NAME
.Nm ace
.Nd
.Tn ACC
10 Mb/s Ethernet interface
.Sh SYNOPSIS
.Cd "device ace0 at vba? csr 0xffff0000 flags 0xfff80000 vector acecint acerint"
.Sh DESCRIPTION
The
.Nm ace
interface provides access to a 10 Mb/s Ethernet network through
an
.Tn ACC
controller.
.Pp
The hardware has 32 kilobytes of dual-ported memory on the
.Tn VERSAbus . 
This memory
is used for internal buffering by the board, and the interface code reads
the buffer contents directly through the
.Tn VERSAbus .
The address of this memory is given in the
.Ar flags
field
in the configuration file.
.Pp
Each of the host's network addresses
is specified at boot time with an
.Dv SIOCSIFADDR
.Xr ioctl 2 .
The
.Nm ace
interface employs the address resolution protocol described in
.Xr arp 4
to dynamically map between Internet and Ethernet addresses on the local
network.
.Pp
The interface normally tries to use a
.Dq trailer
encapsulation
to minimize copying data on input and output.
The use of trailers is negotiated with
.Tn ARP .
This negotiation may be disabled, on a per-interface basis,
by setting the
.Dv IFF_NOTRAILERS
flag with an
.Dv SIOCSIFFLAGS
.Xr ioctl .
.Pp
The device implements an exponential backoff algorithm
when notified of a collision on the cable.  This algorithm utilizes
a table of random numbers setup by the system at boot time.
The delay is done in the controller.
.Sh DIAGNOSTICS
.Bl -diag
.It "ace%d: stray xmit interrupt, xnct %d."
An unexpected transmission complete interrupt was received;
the interrupt is ignored.
.It "ace%d: can't handle af%d."
The interface was handed
a message with addresses formatted in an unsuitable address
family; the packet was dropped.
.El
.Sh SEE ALSO
.Xr intro 4 ,
.Xr inet 4 ,
.Xr arp 4
.Sh HISTORY
The
.Nm
driver appeared in
.Bx 4.3 tahoe .
.Sh BUGS
The hardware is not capable of talking to itself.  The software
implements local sending and broadcast by sending such packets to the
loop interface.  This is a kludge.
.Pp
The device doesn't autoconfigure its interrupt vector; it is set
at 0x90 + eight times the unit number.