Mac OS 9 Lives
Mac OS 9 Discussion => Mac OS 9, Hacks & Upgrades => Topic started by: UnexpectedBomb on July 12, 2026, 01:18:03 PM
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Hi all,
I've been wishing I could get eyes on my MDD CPU temp for a long time, always worrying that it could be cooking without me knowing it, so I began working on a little side project that, to my knowledge, didn't previously exist: a Control Strip module that shows live CPU and case temperature under Mac OS 9 on the G4 MDD, reading straight from the machine's real hardware sensors.
https://github.com/UnexpectedBomb/MacOS9-G4-CPU-Temp
I was aware of a similar CSM existing in "Jeremy's CSM Bundle" but that one reads the PowerPC's on-chip Thermal Assist Unit (TAU). Motorola disabled the TAU on the 7450/7455 family, so on an MDD (and other Apollo-based G4s) it can't give you a real reading at all. This module ignores the TAU entirely and talks over the Uni-N / "KeyWest" I²C bus to the same chips Apple's firmware uses:
- DS1775 digital thermometer to get CPU temperature (within 0.5 °C accuracy, vs the TAU's ±12 °C spec)
- ADM1030 fan controller's local sensor to get case temperature
What it does:
- Shows CPU or case temperature right in the Control Strip, updating every couple of seconds
- Click the tile for a menu: pick the reading (CPU / Case) and the units (°F / °C) as two independent groups
- Text turns red as the CPU approaches its safe limit
- A Notification Manager alert pops up if the CPU ever exceeds the safe threshold (latched — it warns once, not in a loop) to prevent your CPU(s) from getting extra toasty
- Native look: bold text, fixed-width cell, custom Control-Strip-style icon
- Loads silently at startup like any stock module
It is strictly read-only on the hardware. It only reads the sensor temperature registers as an SMBus master. It never writes a sensor, fan, or config register, so it can't interfere with the ADM1030's automatic fan control. (I did try to add a fan-RPM readout, but that requires enabling the ADM1030's tachometer via a config write, and on my machine that audibly disturbed the fan... it was very angry with me... so I dropped it. Not worth frying anything!)
Give it a test-drive and let me know your experience; hopefully it gives you sane readings. I haven't tested on anything other than my MDD (FW400) so if there's other models it's compatible with, please let me know what hardware you used and how it went.
This was developed in parallel with another Mac OS 9 effort of mine, one that I think will be very exciting once it's done... you should be hearing about it hopefully later this month ;)
-UB
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I've been wishing for this for years.
I'll try it on my 2003 MDD with Sonnet MDX 2x1.8 Ghz.
I'll report back.