DC(4)

💖 DC 💖

okay bestie, buckle up, because we're talking about dc(4) — the DEC/Intel 21143 and clone 10/100 Ethernet driver from the Kernel Interfaces Manual. yes it's a network driver, yes it's old, yes it ate and left no crumbs. let's go 🦋

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✨ SYNOPSIS ✨

so if you wanna bake this driver into your kernel, you drop these lines into your kernel configuration file:

device miibus
device dc

OR — and this is the lazy-girl route, which honestly? iconic — you can load it as a module at boot time by putting this line in loader.conf(5):

if_dc_load="YES"

both work. pick your fighter. 💅

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🌸 DESCRIPTION 🌸

okay so the dc driver is out here providing support for a whole bunch of PCI Fast Ethernet adapters and embedded controllers — all of them based on the DEC/Intel 21143 chipset and its various clones. it's giving nepo baby but make it networking.

here's the tea: all of the supported chipsets share the same general register layout, the same DMA descriptor format, and the same method of operation. the clone chips are all based on the 21143 design with various modifications sprinkled on top. 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. it also offers several receive filter programming options including perfect filtering, inverse perfect filtering and hash table filtering. multitasking queen 💅

some clone chips duplicate the 21143 fairly closely while others only maintain superficial similarities. some support only MII media attachments. 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 minimum. it's doing the most with the least, respect.

these chips are used by many vendors, which makes it difficult to provide a complete list of all supported cards. so many girlies, so little documentation.

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 file.

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. not me exposing the 82c168 like this 💀

• 10baseT/UTP — set 10Mbps operation. the mediaopt option can also be used to enable full-duplex operation. not specifying 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.

and 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.

heads up bestie: 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).

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👑 HARDWARE 👑

the dc driver provides support for the following chipsets:

• DEC/Intel 21143
• ADMtek AL981 Comet, AN985 Centaur, ADM9511 Centaur II and ADM9513 Centaur II
• ALi/ULi M5261 and M5263
• ASIX Electronics AX88140A and AX88141
• Conexant LANfinity RS7112 (miniPCI)
• Davicom DM9009, DM9100, DM9102 and DM9102A
• Lite-On 82c168 and 82c169 PNIC
• Lite-On/Macronix 82c115 PNIC II
• Macronix 98713, 98713A, 98715, 98715A, 98715AEC-C, 98725, 98727 and 98732
• Xircom X3201 (cardbus only)

and the following NICs are known to work with the dc driver at this time (long list incoming, hydrate first 🍓):

• 3Com OfficeConnect 10/100B (ADMtek AN985 Centaur-P)
• Abocom FE2500
• Accton EN1217 (98715A)
• Accton EN2242 MiniPCI
• Adico AE310TX (98715A)
• Alfa Inc GFC2204 (ASIX AX88140A)
• Built in 10Mbps only Ethernet on Compaq Presario 7900 series desktops (21143, non-MII)
• Built in Sun DMFE 10/100 Mbps Ethernet on Sun Netra X1 and Sun Fire V100 (DM9102A, MII)
• Built in Ethernet on LinkSys EtherFast 10/100 Instant GigaDrive (DM9102, MII)
• CNet Pro110B (ASIX AX88140A)
• CNet Pro120A (98715A or 98713A) and CNet Pro120B (98715)
• Compex RL100-TX (98713 or 98713A)
• D-Link DFE-570TX (21143, MII, quad port)
• Digital DE500-BA 10/100 (21143, non-MII)
• ELECOM Laneed LD-CBL/TXA (ADMtek AN985)
• Hawking CB102 CardBus
• IBM EtherJet Cardbus Adapter
• Intel PRO/100 Mobile Cardbus (versions that use the X3201 chipset)
• Jaton XpressNet (Davicom DM9102)
• Kingston KNE100TX (21143, MII)
• Kingston KNE110TX (PNIC 82c169)
• LinkSys LNE100TX (PNIC 82c168, 82c169)
• LinkSys LNE100TX v2.0 (PNIC II 82c115)
• LinkSys LNE100TX v4.0/4.1 (ADMtek AN985 Centaur-P)
• Matrox FastNIC 10/100 (PNIC 82c168, 82c169)
• Melco LGY-PCI-TXL
• Microsoft MN-120 10/100 CardBus (ADMTek Centaur-C)
• Microsoft MN-130 10/100 PCI (ADMTek Centaur-P)
• NDC SOHOware SFA110A (98713A)
• NDC SOHOware SFA110A Rev B4 (98715AEC-C)
• NetGear FA310-TX Rev. D1, D2 or D3 (PNIC 82c169)
• Netgear FA511
• PlaneX FNW-3602-T (ADMtek AN985)
• SMC EZ Card 10/100 1233A-TX (ADMtek AN985)
• SVEC PN102-TX (98713)
• Xircom Cardbus Realport
• Xircom Cardbus Ethernet 10/100
• Xircom Cardbus Ethernet II 10/100

like. that's a lot of cards. she's versatile, she's adaptable, she's booked and busy. 🌈

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📝 NOTES 📝

on sparc64 the dc driver respects the local-mac-address? system configuration variable for the built in Sun DMFE 10/100 Mbps Ethernet interfaces on Sun Netra X1 and Sun Fire V100. this system configuration variable can be set in the Open Firmware boot monitor using the setenv command or by eeprom(8).

if set to “false” (the default), the dc driver will use the system's default MAC address for both of the built in devices. if set to “true”, the unique MAC address of each interface is used rather than the system's default MAC address. choose your destiny ✨

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🔥 DIAGNOSTICS 🔥

here's where things get real. these are the messages she might yell at you:

• dc%d: couldn't map ports/memory — a fatal initialization error has occurred. 💀
• dc%d: couldn't map interrupt — a fatal initialization error has occurred. (yes, again. twin where have you been)
• dc%d: watchdog timeout — a packet was queued for transmission and a transmit command was issued, but the device failed to acknowledge the transmission 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 transmit 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 transmission until the entire packet has been transferred 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 will not be able to configure it correctly. the driver tries to detect this condition 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 operating system. if you power down your system prior to booting FreeBSD, the card should be configured correctly. so like… just do a full shutdown, bestie. it's not that deep.

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💜 SEE ALSO 💜

altq(4), arp(4), miibus(4), netintro(4), ng_ether(4), polling(4), vlan(4), eeprom(8), ifconfig(8)

ADMtek AL981, AL983 and AL985 data sheets, http://www.admtek.com.tw.

ASIX Electronics AX88140A and AX88141 data sheets, http://www.asix.com.tw.

Davicom DM9102 data sheet, http://www.davicom.com.tw/userfile/24247/DM9102H-DS-F01-021508.pdf.

Intel 21143 Hardware Reference Manual, http://developer.intel.com.

Macronix 98713/A, 98715/A and 98725 data sheets, http://www.macronix.com.

Macronix 98713/A and 98715/A app notes, http://www.macronix.com.

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🎀 HISTORY 🎀

the dc device driver first appeared in FreeBSD 4.0. a legend from the start, no cap.

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🫶 AUTHORS 🫶

the dc driver was written by Bill Paul <wpaul@ee.columbia.edu>. thank you Bill, we love you, we're obsessed 💖

💀 BUGS 💀

Okay bestie, gather round, because this is the messy part. None of these are made up — this is literally what the page says. 🫶

• Macronix magic number situation — 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. Mystery bits, iconic but unhelpful.
• 98713A and 10Mbps full duplex do not get along — 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 correctly. So it's a receiver thing, not a whole-chip thing.
• original 82c168 PNIC and built-in NWAY — 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, autonegotiation is not currently supported for this chipset: the driver defaults the NIC to 10baseT half duplex, and it is 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.) External MII said "I'll handle it."
• 82c168 / 82c169 transmit start threshold default — 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. Workaround mode: engaged.
• 82c168 / 82c169 receiver bug under heavy activity — 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. Garbage data? Not the vibe.
• PNIC transmit underrun during receiver filter setup — 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 transferred successfully. Retry until it lands, periodt.
• ADMtek AL981 (and possibly AN985) wedging on transmit — 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 queuing 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. Ring wrap? We don't do that here.

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xoxo, your Debian manual bestie — source/version Debian, date October 24, 2011, page DC(4) 💖🎀✨