Resolved MacBook Air strange behavior while powered off

[revmacian]

This incident involves a MacBook Air (Retina, 13-inch, 2019), 8GB RAM, 128GB SSD. I take excellent care of my MBA, I don't even allow food or drink around it.

I powered off my machine and had forgotten bout it. This morning I pressed the Space key to wake the machine and it displayed the Apple logo.. the machine was powering up and I had forgotten that I powered it off. So, from the login screen I clicked the Shutdown button at the bottom of the screen to power off the machine - I was curious and wanted to test something. After it was powered off I pressed the "S" key and the machine began to power up (Apple logo again). I tried this with some of the other keys and the result was the same.

Pressing any key powers up the machine? How is that possible when the machine shouldn't be running at all? I mean, if the machine can detect a keypress then there is some part of the operating system running that detects the keypress. Isn't the kernel involved when a hardware state change is detected and acted upon? Do the newer MacBook Air/Pro models ever truly power down? I ask this because if it were truly powered down, then the machine wouldn't know that a key was pressed.

If you have a 2019/2018 MacBook Air/Pro, could you test this scenario and post your results? I'm curious how far back this goes.

 

[mollyc]

Yes, this is described on the Apple website.

https://support.apple.com/en-us/HT201150

Additionally, MacBook Pro (2018) and MacBook Air (Retina, 13-inch, 2018) turn on when you press any key on the keyboard or press the trackpad.

 

[revmacian]

Yes, this is described on the Apple website.

https://support.apple.com/en-us/HT201150

Thank you very much for that link. The information therein leads me to believe that the machine is never truly powered down. Something has to be running for the machine to be able to detect a keypress while the machine is in a powered down state. So, what happens when the battery is depleted to the point that there is not enough battery life to detect a keypress? Whatever was running to detect a keypress is now no longer running and we can't turn on the machine, after a recharge, because it won't detected a keypress. This seems like a software deep "sleep" state rather than a truly powered down state.

 

[casperes1996]

Thank you very much for that link. The information therein leads me to believe that the machine is never truly powered down. Something has to be running for the machine to be able to detect a keypress while the machine is in a powered down state. So, what happens when the battery is depleted to the point that there is not enough battery life to detect a keypress? Whatever was running to detect a keypress is now no longer running and we can't turn on the machine, after a recharge, because it won't detected a keypress. This seems like a software deep "sleep" state rather than a truly powered down state.

... When you press the power button on any other device, how is that any different? The difference is a dedicated key vs. all keys, but behaviour isn't really any different.

I don't know the exact details of how this is implemented, but it's definitely not related to operating system code, I can tell you that much. At most a firmware chip and even then, it'll not be a problem if It entirely loses charge, as it won't require anything but to receive power again to work, which wouldn't be gated if that were the case.

 

[revmacian]

... When you press the power button on any other device, how is that any different? The difference is a dedicated key vs. all keys, but behaviour isn't really any different.

I don't know the exact details of how this is implemented, but it's definitely not related to operating system code, I can tell you that much. At most a firmware chip and even then, it'll not be a problem if It entirely loses charge, as it won't require anything but to receive power again to work, which wouldn't be gated if that were the case.

A hardware power button is normally a physical switch that is located within the power distribution path. The regular keys (numbers, letters, etc.) are not within the power distribution path because they don't have anything to do with changing the power state of the machine. It now appears that every button is a "power button" so there is no need to have a dedicated "power button". Making every key a power button requires a huge re-working of the circuit board.

Ah, yes, a firmware chip that detects a keypress, that makes sense. I wonder if that is one of the functions of the T2 chip. I also wonder if the butterfly mechanism was important in the creation of the every-key-is-a-power-key keyboard and that is why Apple didn't want to give up on the butterfly keyboard so easily.

 

[casperes1996]

A hardware power button is normally a physical switch that is located within the power distribution path. The regular keys (numbers, letters, etc.) are not within the power distribution path because they don't have anything to do with changing the power state of the machine. It now appears that every button is a "power button" so there is no need to have a dedicated "power button". Making every key a power button requires a huge re-working of the circuit board.

Yes and no. For a long time power buttons on computers have been more sophisticated than that. If you tap the power button on a 2014 MacBook Pro for instance, if it is already turned on, the OS will react to it, not the power circuitry. Hold it for a few seconds, the OS gets an call to sleep. Clearly more is going on than just wiring it to the power directly even back then.

Ah, yes, a firmware chip that detects a keypress, that makes sense. I wonder if that is one of the functions of the T2 chip. I also wonder if the butterfly mechanism was important in the creation of the every-key-is-a-power-key keyboard and that is why Apple didn't want to give up on the butterfly keyboard so easily.

Doubt there's anything that couldn't be done easily with a traditional keyboard switch.

 

[revmacian]

Yes and no. For a long time power buttons on computers have been more sophisticated than that. If you tap the power button on a 2014 MacBook Pro for instance, if it is already turned on, the OS will react to it, not the power circuitry. Hold it for a few seconds, the OS gets an call to sleep. Clearly more is going on than just wiring it to the power directly even back then.



Doubt there's anything that couldn't be done easily with a traditional keyboard switch.

Thank you for your explanations, you've helped me to better understand my machine and you really cannot put a price on that. It is clear that my understanding of electronics would benefit from an upgrade.

 

[Clix Pix]

When I bought my 2017 12" MacBook two years ago I was startled when I lifted the lid and the thing powered up before I was quite ready to do anything with it -- that was my introduction to the new way of doing things! That machine, however, once shut down does not power up when the lid is open and I touch any of the keys. It took a little getting-used-to with the 2018 MBP to have the lid remaining open with the machine shut down and when I touch any key and it powers on!

 

[casperes1996]

Thank you for your explanations, you've helped me to better understand my machine and you really cannot put a price on that. It is clear that my understanding of electronics would benefit from an upgrade.

I'd just like to add the disclaimer that I could use such an upgrade as well, and when it comes to hardware and power delivery I'm far from an expert. My knowledge is mostly in software, and the overlaps where software needs to know about hardware, but purer electronics I'm not the greatest at, so what I say is true based on my understanding of things and such, but yeah, I won't claim expertship on this.

 

[revmacian]

When I bought my 2017 12" MacBook two years ago I was startled when I lifted the lid and the thing powered up before I was quite ready to do anything with it -- that was my introduction to the new way of doing things! That machine, however, once shut down does not power up when the lid is open and I touch any of the keys. It took a little getting-used-to with the 2018 MBP to have the lid remaining open with the machine shut down and when I touch any key and it powers on!

Yes, it does take some getting used to. I'm guessing it is the T2 chip that has something to do with keypress detection. I'm also guessing that the only reason for a "power button" now is dual duty as a fingerprint reader.

There are indeed interesting times!