LPT(4)

💖 LPT(4) — the kernel interfaces manual, bestie edition 🎀

okay so real talk — this is lpt(4) from the Kernel Interfaces Manual, and it's basically the glow-up story of a printer driver. sit down, grab a boba, we're learning about parallel ports 🌸

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✨ NAME ✨

lpt — the generic printer device driver, aka the icon that handles your printing era 👑

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🦋 SYNOPSIS 🦋

device ppc
device ppbus
device lpt

three little lines, one big vibe. that's the whole config, no cap 💅

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🌈 DESCRIPTION 🌈

okay so the current lpt driver is literally the port of the original lpt driver to the ppbus(4) system. a rebrand, but make it functional ✨

one purpose of this port was to allow parallel port sharing with other parallel devices — yes bestie, sharing, we love a driver that plays nice 🫶

secondly, the inb()/outb() calls have been replaced by ppbus function calls. and because of that, lpt is now arch-independent thanks to the ppbus interface. so it works everywhere, it's giving main character energy across all architectures 😌

see ppbus(4) for more info about the ppbus system — that's the lore, go read it 📚

now the tea about the bus: the parallel port bus is allocated by lpt when the printer device is opened, and it's released only when the transfer is completed — which is either when:

• the device is closed, or
• the entire buffer is sent in interrupt driven mode 💫

the driver can be configured to be either interrupt-driven or to poll the printer. and here's the cute part: ports that are configured to be interrupt-driven can be switched to polled mode by using the lptcontrol(8) command. flexibility? we stan 🔥

depending on your hardware, extended capabilities may be configured with the lptcontrol(8) command. and with an ECP/ISA port, you can take advantage of FIFO and DMA — fancy hardware gets fancy features, iykyk 💜

last thing, and it's a fun one: in order to retrieve printer info from /dev/lpt0, just apply the cat command to the device 🐈

cat /dev/lpt0

if the printer supports IEEE1284 nibble mode and has data to send to the host, you will get it. literally just vibes and bytes coming at you, slay ⭐

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🎀 FILES 🎀

• /dev/lpt0 — the first parallel port driver. first, as in the main character of parallel ports 👑

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🌸 SEE ALSO 🌸

• ppbus(4) — the whole ppbus system, go get educated bestie
• ppc(4) — parallel port chipset driver, the friend group member
• lptcontrol(8) — the command that changes modes and configures your extended capabilities

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💫 HISTORY 💫

this driver replaces the functionality of the lpa driver, which is now defunct. lpa? never heard of her 🙈 RIP bozo, but respectfully 💀

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💀 BUGS 💀

okay so buckle up, we're in our honest era:

• there are lots of them — especially in cheap parallel port implementations. cheap hardware, cheap thrills, expensive problems 😭
• it is only possible to open a lpt port when a printer is connected and on-line — which makes it impossible to run lptcontrol(8) when there is no printer connected. yes, that's as annoying as it sounds. a whole catch-22, fr fr 🫠
• and finally: this driver could still stand a rewrite. the devs said it themselves, no notes 🔥

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and that's the page!! 🧚 written under Debian, dated February 14, 1999 — a Valentine's Day gift to parallel ports everywhere 💖 mwah, go print something pretty 🎀