![]() The answer is, as long as the Intel side of your Mac is shut down, you can’t tell the normal from the broken. Just how long should take, and how can you tell if something has gone wrong, and your Mac is now frozen? So the only sensible course is to leave your Mac alone, staring alternately at its black screen and your watch. At worst, if that were to be done during a firmware update, it could damage the update, and then you’ll be nervously trying to perform a firmware restore, and worrying whether your Mac is now bricked. At best it will get you nowhere, as you’ll then need to start your Mac up again, and face the same black screen purgatory. Worse still is the fact that the only thing you can do is press the Power button to force your Mac to shut down, which is one action with the highest risk of making your problems far worse. Hearing of many T2 Macs which have managed somehow to brick themselves with a firmware problem, it’s natural that the user should come to suspect that’s the cause of the continuing black screen. But as time passes, it becomes more suspiciously the result of catastrophe. For the first thirty seconds or so, the black screen doesn’t cause any anxiety. The snag is that every Mac user has learned the meaning of a black screen: that Mac has been shut down, or has frozen and can’t recover except by rebooting. During much of this period in the update, the Intel side has to be shut down, providing the user with just a black screen to gaze at. ![]() This involves downloading it direct from Apple, checking it, and its installation. This situation is even more critical when the firmware of the T2 chip is to be updated. During those checks, there’s a phase in which the Intel side of the Mac has to be shut down, preventing any graphics display – hence the black screen, as the display is driven from the main chipset, not the T2. If they don’t match, integrity information may be needed to be downloaded from Apple before deciding whether to reinstall macOS or lower the security level. When a Mac with a T2 chip is starting up in its standard full security mode, once the user has entered their password in the login screen to give access to the startup disk, the T2 has to compare the signature of its boot loader and other components against a value saved in its NVRAM. I have described in some detail the main stages of the boot process, which are summarised in the diagram below. So why do they occur, and what can you do about them? ![]() If you have a Mac, even one as blisteringly fast as an iMac Pro or a high-end mini or MacBook Pro, these black screens are always worryingly long. The temptation to force it to shut down steadily increases, until at long last it shows signs of life again. The same happens whenever it updates its firmware: the display goes black, and it plays dead for at least a couple of minutes. It started up briskly, I logged in, then it showed a black screen for so long that I gave up waiting for it and got on with other tasks. This has a T2 chip, and FileVault is active on its internal SSD. The other day, I was in a hurry, but needed to restart my iMac Pro which had just completed cleaning up my Time Machine backups.
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