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DC(4)                  FreeBSD Kernel Interfaces Manual                  DC(4)

     dc -- DEC/Intel 21143 and clone 10/100 ethernet driver

     device miibus
     device dc

     The dc driver provides support for several PCI fast ethernet adapters and
     embedded controllers based on the following chipsets:

           +o   DEC/Intel 21143
           +o   Macronix 98713, 98713A, 98715, 98715A and 98725
           +o   Davicom DM9100, DM9102 and DM9102A
           +o   ASIX Electronics AX88140A and AX88141
           +o   ADMtek AL981 Comet and AN985 Centaur
           +o   Lite-On 82c168 and 82c169 PNIC
           +o   Lite-On/Macronix 82c115 PNIC II
           +o   Conexant LANfinity RS7112 (miniPCI)

     All of these chips have the same general register layout, DMA descriptor
     format and method of operation.  All of the clone chips are based on the
     21143 design with various modifications.  The 21143 itself has support
     for 10baseT, BNC, AUI, MII and symbol media attachments, 10 and 100Mbps
     speeds in full or half duplex, built in NWAY autonegotiation and wake on
     LAN.  The 21143 also offers several receive filter programming options
     including perfect filtering, inverse perfect filtering and hash table

     Some clone chips duplicate the 21143 fairly closely while others only
     maintain superficial similarities.  Some support only MII media attach-
     ments.  Others use different receiver filter programming mechanisms.  At
     least one supports only chained DMA descriptors (most support both
     chained descriptors and contiguously allocated fixed size rings). Some
     chips (especially the PNIC) also have peculiar bugs.  The dc driver does
     its best to provide generalized support for all of these chipsets in
     order to keep special case code to a minimun.

     These chips are used by many vendors which makes it difficult to provide
     a complete list of all supported cards.  The following NICs are known to
     work with the dc driver at this time:

           +o   Digital DE500-BA 10/100 (21143, non-MII)
           +o   Built in DE500-BA on DEC Alpha workstations (21143, non-MII)
           +o   Built in 10Mbps only ethernet on Compaq Presario 7900 series
               desktops (21143, non-MII)
           +o   Built in ethernet on LinkSys EtherFast 10/100 Instant GigaDrive
               (DM9102, MII)
           +o   Kingston KNE100TX (21143, MII)
           +o   D-Link DFE-570TX (21143, MII, quad port)
           +o   NDC SOHOware SFA110 (98713A)
           +o   SVEC PN102-TX (98713)
           +o   CNet Pro120A (98715A or 98713A) and CNet Pro120B (98715)
           +o   Compex RL100-TX (98713 or 98713A)
           +o   LinkSys LNE100TX (PNIC 82c168, 82c169)
           +o   NetGear FA310-TX Rev. D1, D2 or D3 (PNIC 82c169)
           +o   Matrox FastNIC 10/100 (PNIC 82c168, 82c169)
           +o   Kingston KNE110TX (PNIC 82c169)
           +o   LinkSys LNE100TX v2.0 (PNIC II 82c115)
           +o   Jaton XpressNet (Davicom DM9102)
           +o   Alfa Inc GFC2204 (ASIX AX88140A)
           +o   CNet Pro110B (ASIX AX88140A)

     The dc driver supports the following media types:

     autoselect            Enable autoselection of the media type and options.
                           The user can manually override the autoselected
                           mode by adding media options to the /etc/rc.conf

                           Note: the built-in NWAY autonegotiation on the
                           original PNIC 82c168 chip is horribly broken and is
                           not supported by the dc driver at this time (see
                           the BUGS section for details).  The original 82c168
                           appears on very early revisions of the LinkSys
                           LNE100TX and Matrox FastNIC.

     10baseT/UTP           Set 10Mbps operation.  The mediaopt option can also
                           be used to enable full-duplex operation.  Not spec-
                           ifying full duplex implies half-duplex mode.

     100baseTX             Set 100Mbps (fast ethernet) operation.  The
                           mediaopt option can also be used to enable
                           full-duplex operation.  Not specifying full duplex
                           implies half-duplex mode.

     The dc driver supports the following media options:

     full-duplex           Force full duplex operation.  The interface will
                           operate in half duplex mode if this media option is
                           not specified.

     Note that the 100baseTX media type may not be available on certain Intel
     21143 adapters which support 10mbps media attachments only.  For more
     information on configuring this device, see ifconfig(8).

     dc%d: couldn't map ports/memory  A fatal initialization error has

     dc%d: couldn't map interrupt  A fatal initialization error has occurred.

     dc%d: watchdog timeout  A packet was queued for transmission and a trans-
     mit command was issued, but the device failed to acknowledge the trans-
     mission before a timeout expired.  This can happen if the device is
     unable to deliver interrupts for some reason, of if there is a problem
     with the network connection (cable or network equipment) that results in
     a loss of link.

     dc%d: no memory for rx list  The driver failed to allocate an mbuf for
     the receiver ring.

     dc%d: TX underrun -- increasing TX threshold  The device generated a
     transmit underrun error while attempting to DMA and transmit a packet.
     This happens if the host is not able to DMA the packet data into the
     NIC's FIFO fast enough.  The driver will dynamically increase the trans-
     mit start threshold so that more data must be DMAed into the FIFO before
     the NIC will start transmitting it onto the wire.

     dc%d: TX underrun -- using store and forward mode  The device continued
     to generate transmit underruns even after all possible transmit start
     threshold settings had been tried, so the driver programmed the chip for
     store and forward mode.  In this mode, the NIC will not begin transmis-
     sion until the entire packet has been transfered into its FIFO memory.

     dc%d: chip is in D3 power state -- setting to D0  This message applies
     only to adapters which support power management.  Some operating systems
     place the controller in low power mode when shutting down, and some PCI
     BIOSes fail to bring the chip out of this state before configuring it.
     The controller loses all of its PCI configuration in the D3 state, so if
     the BIOS does not set it back to full power mode in time, it won't be
     able to configure it correctly.  The driver tries to detect this condi-
     tion and bring the adapter back to the D0 (full power) state, but this
     may not be enough to return the driver to a fully operational condition.
     If you see this message at boot time and the driver fails to attach the
     device as a network interface, you will have to perform a second warm
     boot to have the device properly configured.

     Note that this condition only occurs when warm booting from another oper-
     ating system.  If you power down your system prior to booting FreeBSD,
     the card should be configured correctly.

     arp(4), miibus(4), netintro(4), ng_ether(4), ifconfig(8)

     ADMtek AL981, AL983 and AL985 data sheets,

     ASIX Electronics AX88140A and AX88141 data sheets,

     Davicom DM9102 data sheet,

     Intel 21143 Hardware Reference Manual,

     Macronix 98713/A, 98715/A and 98725 data sheets,

     Macronix 98713/A and 98715/A app notes,

     The dc device driver first appeared in FreeBSD 4.0.

     The dc driver was written by Bill Paul <>.

     The Macronix application notes claim that in order to put the chips in
     normal operation, the driver must write a certain magic number into the
     CSR16 register.  The numbers are documented in the app notes, but the
     exact meaning of the bits is not.

     The 98713A seems to have a problem with 10Mbps full duplex mode.  The
     transmitter works but the receiver tends to produce many unexplained
     errors leading to very poor overall performance.  The 98715A does not
     exhibit this problem.  All other modes on the 98713A seem to work cor-

     The original 82c168 PNIC chip has built in NWAY support which is used on
     certain early LinkSys LNE100TX and Matrox FastNIC cards, however it is
     horribly broken and difficult to use reliably.  Consequently, autonegoti-
     ation is not currently supported for this chipset: the driver defaults
     the NIC to 10baseT half duplex, and it's up to the operator to manually
     select a different mode if necessary.  (Later cards use an external MII
     transceiver to implement NWAY autonegotiation and work correctly.)

     The dc driver programs 82c168 and 82c169 PNIC chips to use the store and
     forward setting for the transmit start threshold by default.  This is to
     work around problems with some NIC/PCI bus combinations where the PNIC
     can transmit corrupt frames when operating at 100Mbps, probably due to
     PCI DMA burst transfer errors.

     The 82c168 and 82c169 PNIC chips also have a receiver bug that sometimes
     manifests during periods of heavy receive and transmit activity, where
     the chip will improperly DMA received frames to the host.  The chips
     appear to upload several kilobytes of garbage data along with the
     received frame data, dirtying several RX buffers instead of just the
     expected one.  The dc driver detects this condition and will salvage the
     frame; however, it incurs a serious performance penalty in the process.

     The PNIC chips also sometimes generate a transmit underrun error when the
     driver attempts to download the receiver filter setup frame, which can
     result in the receive filter being incorrectly programmed.  The dc driver
     will watch for this condition and requeue the setup frame until it is
     transfered successfully.

     The ADMtek AL981 chip (and possibly the AN985 as well) has been observed
     to sometimes wedge on transmit: this appears to happen when the driver
     queues a sequence of frames which cause it to wrap from the end of the
     transmit descriptor ring back to the beginning.  The dc driver attempts
     to avoid this condition by not queing any frames past the end of the
     transmit ring during a single invocation of the dc_start() routine.  This
     workaround has a negligible impact on transmit performance.

FreeBSD 4.10                   November 20, 1999                  FreeBSD 4.10


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