No firmware is required. Macbooks manufactured since 2014 turn on the LED whenever any power is supplied to the camera sensor, and force the LED to remain on for at least 3 seconds.

(Source: I architected the feature)

Thanks for your reply — yourself as the Source can only make me feel flattered then for you responding to me.

> Macbooks manufactured since 2014 turn on the LED whenever any power is supplied to the camera sensor, and force the LED to remain on for at least 3 seconds.

That convinced me originally I think, good old days! I'd almost forgotten about it. The way you phrased it, it sounded like 50% OS concern to me.

But if cam & LED rly share a power supply, and the LED is always on without any external switch, Good then!

I was not very popular with the camera firmware folks for a while. They had to re-architect a bunch of things as they used to occasionally power on the camera logic without powering the sensor array to get information out of the built-in OTP. Because the LED now came on whenever the camera was powered they had to defer all that logic.

What does OTP stand for in this case? The camera PROM??

Apologies. OTP is One-Time-Programmable. The physical implementation of this varies, in this specific case it was efuses (anti-fuse, actually). It's used for things like calibration data. For a camera it contains information about the sensor (dead pixels, color correction curves, etc.).