The author did not test the DFU flow, so I'm not sure why they're blaming the DFU port documentation.

Certainly there is a bug in the external disk upgrade sequence if switching the disk to a different (also non-DFU? They didn't specify) port solved their problem. But that's not necessarily related to which port is the DFU port.

To be clear, DFU (Device Firmware Upgrade) is a standard USB protocol (from 2004!), for a device to receive upgrades from a host. It is a specific port on the mac because that's all the boot-rom can support. This system does not come into play when booting from or upgrading an external disk, as the author was struggling with, because the external disk cannot be a USB Host to drive the DFU.

And I'm guessing that the reason macOS doesn't give more details is because macOS is likely not involved in the step that fails (maybe iBoot is?), and they didn't develop a way for the failing step to communicate failure data back to macOS. Yet another UX failure.

▲ numpad0 3 hours ago | parent | next [-]

  Situation:
  - The author is running macOS ARM64  
  - off of a USB disk  
      - plugged into DFU capable USB-C port    
      - that shouldn't be the DFU one according to docs
  - attempting to run macOS updater  
  - (supposedly)there's nothing else connected to it  

  Outcomes:  
  - updates were failing and rolling back with cryptic errors  
  - errors persist despite all efforts  
  - -> later magically solved after changing the port  
  - -> the problematic port later revealed to be the DFU port  
      - contradictory to Apple documentation

Or at least that's how it reads to me. As for reasons, I don't know why anything that can boot from USB can't from DFU-enabled USB port, but maybe it's configured as a special non-USB debug connector while bootloader is executing.

	▲	AceJohnny2 2 hours ago \| parent [-]
		`- plugged into DFU capable USB-C port` This is what I'm contending. No, I don't think this is true. All he found was the upgrading macOS on the external disk, which as documented must not be on a DFU capable USB-C port, did not work when plugged into a port that was documented to not be DFU. The source the author is referring to, Michael Tsai, indeed found that he had plugged his external disk into the DFU port. The author then (reasonably, but IMHO erroneously) deduced that his problem, also solved by changing ports, must thus have had the same cause. I say it may be confounding factors, and the only way to validate the wrong DFU port hypothesis is putting their mac in DFU mode and then running Recovery Assistant (from another machine) against it, on various ports. Tangentially, it is infuriating that Apple would swap what the DFU port is across generations, as if it wasn't confusing enough. Also... > As for reasons, I don't know why anything that can boot from USB can't from DFU-enabled USB port, but maybe it's configured as a special non-USB debug connector while bootloader is executing. My guess is it's because DFU requires the port to be in Device mode, whereas booting from a external disk requires the port to be in Host mode. Apple care about boot time, so perhaps they don't want to waste time in the boot process to check the port in Device mode for a few secs, then switch to Host mode to try external disk booting.

▲ 2 hours ago | parent | prev | next [-]

[deleted]

▲ j16sdiz 2 hours ago | parent | prev [-]

The author was not saying the document labeled wrong port as DFU port.

He is saying the documented _behaviour_ of DFU port is wrong (or, at least, in complete.)

	▲	tgma 2 hours ago \| parent [-]
		The post says: > This is wrong, a discovery that took me about a half dozen attempts to update macOS on an external disk. I have a 16-inch MacBook Pro with an M4 chip, specifically an M4 Pro chip, and the DFU port seems to be the USB-C port on the right side of the Mac, not on the left side." It appears that the author is directly contradicting your read.