ADDCOM(4)

💅 ADDCOM(4) — bestie's guide to the multiplexing serial situation

okay so this is a page from the Kernel Interfaces Manual, and it's about addcom, which is giving "one board, many serial ports" realness. let me tell you everything 🫶

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✨ SYNOPSIS ✨

like, here's the config vibe, literally copy it:

addcom0 at isa? port 0x108 irq 5
com* at addcom?

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🌸 DESCRIPTION 🌸

so the addcom driver is out here providing support for Addonics FlexPort 8/S boards — and probably the FlexPort 4/S too, ngl they're pretty sure but not like sure sure. these boards multiplex together up to eight (or four, for the smaller one) EIA RS-232C (CCITT V.28) communications interfaces. iconic honestly. ✨

each addcom device is the master device for up to eight com devices. the way that works: the kernel configuration specifies these com devices as slave devices of the addcom device, exactly like the “SYNOPSIS” shows. 👑

the slave ID you give each com device is what decides which bit in the interrupt multiplexing register gets tested to find interrupts for that device. so like, that number? it matters. don't just put anything. 💅

the port specification for the addcom device is what gets used to compute the base addresses for the com subdevices. cute, right?

⚠️ and here's the part where I hold your hand: the port for the interrupt multiplexing register is fixed, so it is doubtful that more than one addcom can be used in a machine. like, don't count on it, bestie. one board per machine energy. 💀

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🎀 FILES 🎀

• /dev/tty??

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🦋 SEE ALSO 🦋

• com(4)
• intro(4)
• isa(4)

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⭐ HISTORY ⭐

OpenBSD support for addcom devices first appeared in OpenBSD 3.0. historic. a little retro moment for us. 🌈

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and that's the whole page, no notes 💖 this edition was served to you by Debian, dated May 21, 2008 — yeah she's vintage, we stan a classic. mwah 💋✨