JME(4)

💖 JME(4) — the jme girlies' field guide 💖

okay bestie, sit down, hydrate, because we're talking about the jme driver — the JMicron Gigabit/Fast Ethernet driver — and it's giving networking icon energy. this is a Kernel Interfaces Manual page, so like, very serious, very official, but we're gonna make it cute. 🎀

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✨ NAME ✨

jme — the JMicron Gigabit/Fast Ethernet driver. that's her. that's the whole name. slay. 💅

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🦋 SYNOPSIS 🦋

so you wanna get this driver into your kernel? no cap, it's easy. drop these lines in your kernel configuration file:

device miibus
device jme

or, if you're more of a "load it at boot like a module" kinda girl (valid!), put this line in loader.conf(5):

if_jme_load="YES"

boom. done. ✨

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🌸 DESCRIPTION 🌸

the jme device driver provides support for JMicron JMC25x PCI Express Gigabit Ethernet controllers and JMicron JMC26x PCI Express Fast Ethernet controllers. two controller families, one iconic driver, we love to see it. 👑

and listen — all the LOMs supported by jme are absolutely stacked, no crumbs. they all have:

• TCP/UDP/IP checksum offload for both transmit and receive (both!! balanced!!)
• TCP segmentation offload (TSO)
• hardware VLAN tag stripping/insertion features
• Wake On Lan (WOL) — yes she can wake you up, respectfully
• an interrupt coalescing/moderation mechanism
• a 64-bit multicast hash filter

the JMC25x is the overachiever of the family and also supports Jumbo Frames (up to 9216 bytes), which you configure via the interface MTU setting. if you select an MTU larger than 1500 bytes with the ifconfig(8) utility, you're configuring the adapter to receive and transmit Jumbo Frames. periodt. 🫶

💫 media types she supports 💫

• autoselect — enables autoselection of the media type and options. you can manually override the autoselected mode by adding media options to rc.conf(5). letting her choose, but you can step in. main character energy.
• 10baseT/UTP — set 10Mbps operation. slow and steady, still valid.
• 100baseTX — set 100Mbps (Fast Ethernet) operation.
• 1000baseTX — set 1000baseTX operation over twisted pair. gigabit babe.

💅 media options 💅

• full-duplex — force full duplex operation.
• half-duplex — force half duplex operation.

for more info on configuring this device, see ifconfig(8). iykyk. 🌈

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👑 HARDWARE 👑

the jme device driver provides support for the following Ethernet controllers:

• JMicron JMC250 PCI Express Gigabit Ethernet controller
• JMicron JMC251 PCI Express Gigabit Ethernet with Card Read Host controller
• JMicron JMC260 PCI Express Fast Ethernet controller
• JMicron JMC261 PCI Express Gigabit Ethernet with Card Read Host controller

four icons. a whole squad. 🧚

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🔥 LOADER TUNABLES 🔥

tunables can be set at the loader(8) prompt before booting the kernel, or stored in loader.conf(5). your choice, bestie, both are valid.

• hw.jme.msi_disable — this tunable disables MSI support on the Ethernet hardware. the default value is 0.
• hw.jme.msix_disable — this tunable disables MSI-X support on the Ethernet hardware. the default value is 0.

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⭐ SYSCTL VARIABLES ⭐

the following variables are available as both sysctl(8) variables and loader(8) tunables. double duty, she's versatile. 💜

• dev.jme.%d.tx_coal_to — this variable sets the maximum amount of time to delay before sending a Tx completion interrupt, in microseconds. the accepted range is 1 to 65535; the default is 100 (100us).
• dev.jme.%d.tx_coal_pkt — this variable sets the maximum number of outgoing packets which may be coalesced together into a single Tx completion interrupt. the accepted range is 1 to 255; the default is 8.
• dev.jme.%d.rx_coal_to — this variable sets the maximum amount of time to wait for additional packets to arrive (for possible packet coalescing) before firing an Rx completion interrupt, in microseconds. the accepted range is 1 to 65535; the default is 100 (100us).
• dev.jme.%d.rx_coal_pkt — this variable sets the maximum number of incoming packets which may be coalesced into a single Rx completion interrupt. the accepted range is 1 to 255; the default is 2.
• dev.jme.%d.process_limit — this variable sets the maximum number of events that will be processed in a single batch before the handler is requeued into a taskqueue. the accepted range is 10 to 255; the default value is 128 events. the interface does not need to be brought down and up again before a change takes effect. (no dramatic restart required, we love a low-maintenance queen ✨)

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🌈 SEE ALSO 🌈

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

go read those too, they're all part of the extended universe bestie 📚

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💖 HISTORY 💖

the jme driver was written by Pyun YongHyeon <yongari@FreeBSD.org>. it first appeared in FreeBSD 7.1. a legend, an origin story, we stan. 🫶

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😭 CAVEATS 😭

okay bestie this is the part where we get serious, because this is the do not play with this section. no cap.

the eFuse thing. read this twice.

the jme driver tries to avoid unnecessary station address reprogramming for controllers that use eFuse to store station address. the number of times that eFuse can be safely reprogrammed is 16 at most. and it gets worse: there is no way to restore the factory default station address once the station address has been reprogrammed via eFuse.

it is highly recommended not to reprogram the station address, and it is the responsibility of the administrator to store the original station address in a safe place when station address is changed. like, screenshot it, write it on a sticky note, tattoo it, whatever — just don't lose it. 💀

the 1000baseT link drama. two known issues with JMC25x.

1. If the full mask revision number of the JMC25x controller is less than or equal to 4 and the link partner enabled the IEEE 802.3az Energy Efficient Ethernet feature, the controller will not be able to establish a 1000baseT link.
2. Also, if the length of the cable is longer than 120 meters, the controller can not establish a 1000baseT link.

the known workaround for these issues is to force manual link configuration with 100baseTX instead of relying on auto-negotiation. not ideal, but it works, and we adapt. 💅

the full mask revision number of the controller can be checked with the verbose kernel boot option. use the lower nibble of the chip revision number to get the full mask revision of the controller. tiny detail, big consequences. 🙈

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and that's the whole page, bestie!! this was the JME(4) manpage from the Debian crew, dated March 4, 2012 — vintage but still serving. go forth, configure your ethernet, and remember: back up that station address. mwah 💋✨