CM(4) BSD Kernel Interfaces Manual CM(4)
cm -- SMC Arcnet Ethernet device driver
The cm driver provides support for the Arcnet ISA network adapters.
This driver also has quirks preset in the device.hints(5) file for card
The cm driver supports the following card models:
o SMC90c66 in '56 compatibility mode.
When the NOARP flag is set on the cm interface, it does not employ the
address resolution protocol described in arp(4) to dynamically map
between Internet and Ethernet addresses on the local network. Instead it
uses the least significant 8 bits of the IP address as the hardware
address like described in RFC 1051 and RFC 1201.
With the IFF_LINK0 flag cleared IP/ARP/RARP encoding is done according to
RFC 1201 that is, with Packet Header Definition Standard header and
packet type 212 / 213. The MTU is normally 1500. The IFF_LINK0 flag is
cleared by default.
With the IFF_LINK0 flag set, IP and ARP encoding is done according to the
deprecated RFC 1051 encoding, that is with simple header, packet type 240
/ 241, and the MTU is 507.
When switching between the two modes, use
ifconfig interfacename down up
to switch the MTU.
The following driver specific error messages may be reported:
reset: card reset, link addr = 0x%02x (cm%d) The card is being reset and
a new link address assigned.
srint: restarted rx on buf cm%d The rx buffer has been emptied and will
netintro(4), watchdog(4), device.hints(5), ifconfig(8), watchdog(8)
The cm device was ported from NetBSD by Max Khon <fjoeATFreeBSD.org> and
first appeared in FreeBSD 4.6. This manual page first appeared in
This manual page was written by Tom Rhodes <trhodesATFreeBSD.org>. The
IMPLEMENTATION NOTES section was submitted by
Max Khon <fjoeATFreeBSD.org> and originated from NetBSD.
The cm driver code could do with a bit of improvement, it would be nice
if some one could come along and take care of this.
The IMPLEMENTATION NOTES section is specific to all Arcnet devices (see
sys/net/if_arcsubr.c) and should be moved to a more generic location.
BSD July 28, 2004 BSD