DDT(9)

✨ DDT(9) — the HAL Component that's literally just vibing with derivatives 💅

okay bestie, so this is a HAL component manual page, and we're talking about ddt — she computes the derivative of the input function, and honestly? iconic. 🦋

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🌸 NAME 🌸

ddt — Compute the derivative of the input function. that's it, that's the whole job, and she does it flawlessly. periodt. 💖

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🎀 SYNOPSIS 🎀

loadrt ddt [count=N|names=name1[,name2...]]

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👑 DESCRIPTION 👑

ok so listen. every single time the real time thread calls a function, ddt does the math:

it takes the difference between the old and the current input value, and divides that by the timer elapsed since the last call.

that's the derivative, babes. rate of change. slope of the line. no cap. 🔥

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⭐ FUNCTIONS ⭐

• ddt.N — hiii she requires a floating-point thread, just so you know 💅

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🧚 PINS 🧚

• ddt.N.in float in — the input, bestie, feed her numbers 🍓
• ddt.N.out float out — the output, aka the derivative itself, go off 👑

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💀 NOTES 💀

ngl this is important, so read it fr fr.

because this only works on two consecutive input values, it's only gonna work well if the input changes every function call.

it will not work so well if the rate of change is very low and the input doesn't change every time the real time function is called. like, it's giving stale data energy. 😭

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🫶 AUTHOR 🫶

Jeff Epler

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🌈 LICENSE 🌈

GPL

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okay that's the whole page, you're so welcome 💖 this was pulled straight from the LinuxCNC Documentation, dated 2026-03-17, and the manual is called DDT(9). mwah, go compute some derivatives cutie 🎀✨