NPX(4)

📦 version 12.2, in debian bookworm, debian trixie, ubuntu jammy, ubuntu noble, ubuntu questing, ubuntu resolute, ubuntu stonking

💅 NPX(4) — bestie edition 💅

okay so this is from the i386 Kernel Interfaces Manual, and we're about to talk about the Numeric Processing Extension coprocessor. it's giving vintage, it's giving 1993, it's giving "your motherboard is the problem." let's go 🦋

✨ NAME ✨

npx — Numeric Processing Extension coprocessor

🌸 SYNOPSIS 🌸

device npx
hint.npx.0.at="nexus"
hint.npx.0.port="0x0F0"
hint.npx.0.flags="0x0"
hint.npx.0.irq="13"

💖 DESCRIPTION 💖

okay so the npx driver is what lets your system actually use the Numeric Processing Extension coprocessor. no cap. if you've got a 486DX CPU, or you've got a 387 or 487SX coprocessor hanging out in there, congrats, you have numeric processing extensions ✨

and bestie, listen — the npx driver is required for proper system functioning. not optional. not a vibe. if there is no NPX in the system, the system will not boot. that's not me being dramatic, that's literally the manpage. 💀

🎀 the flags for npx0 🎀

these are your little toggles, your switches, your "pls don't optimize this one" buttons:

  • 0x01 — do not use the NPX registers to optimize bcopy.
  • 0x02 — do not use the NPX registers to optimize bzero.
  • 0x04 — do not use the NPX registers to optimize copyin or copyout.

🧚 the optimization vibe check 🧚

so the NPX registers are normally used to optimize copying and zeroing — iconic behavior honestly — but ONLY when all of these conditions are satisfied:

  1. cpu I586_CPU is an option
  2. the CPU is an i586 (perhaps not a Pentium)
  3. the probe for npx0 succeeds
  4. INT 16 exception handling works.

when all that lines up? copying and zeroing using the NPX registers is normally 30-100% faster. literally slay. 🔥

the flags exist so you can control the cases where it does not work or is slower. and setting them at boot time using hints works correctly — because the optimizations are not used until later in the bootstrap when npx0 is attached. iykyk 💅

😭 BUGS 😭

not me having to say this but — there are lots of them, especially on old cheap motherboards. 🙈

in particular, some motherboards do not have the interrupt lines from the NPX to the CPU wired properly. that's it, that's the bug. go yell at your motherboard. 👑

and that's the whole page, bestie 🫶 — this one's from the Debian crew, dated August 28, 1993. yeah. 1993. ancient. historic. iconic. drink some water and check your IRQ wiring 💜

📦 where this page comes from