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iPhone 15 Pro Max can Degrade Thunderbolt Peripherals to USB 2.0 Speed

re: Apple Core Rot

Downloads from your card reader molasses-slow? This drove me crazy!

Summary: first plugging-in the iPhone 15 Pro Max results in USB 2.0 speeds for certain Thunderbolt 3 periphals —  50X to 100X too slow.

Details: macOS Ventura 13.6, 2021 MacBook Pro M1 Max, variety of different Thunderbolt cables.

It took me hours to sort this out, since it depended only on the order in which things were connected. And on the road in my Sprinter van, the iPhone almost always got plugged in first, for internet access.

In my case, I was trying to download using the OWC Atlas FXR card reader, which operates at 1600MB/sec or so for CFExpress Type B cards. But when I plugged it in, it was connecting at USB 2.0 speeds eg about 50X slower than it ought.

Atlas FXR:
Product ID:	0xde60
Vendor ID:	0x1e91
Version:	f0.01
Serial Number:	067345680364
Speed:	Up to 480 Mb/s <=== should be 40000 Mb/sec
Manufacturer:	OWC
Location ID:	0x01100000 / 1
Current Available (mA):	500
Current Required (mA):	500
Extra Operating Current (mA):	0

While running macOS Monterey and using iPhone 7 Plus back in July, no such issue existed. It all came about with macOS Ventura—yet another macOS bug.

What makes this bizarre and surprising is that each port is its own Thunderbolt bus. For one peripheral to affect another peripheral on a different bus is bizarre at best. Still, the iPhone 15 Pro Max is itself super flaky, sometimes connecting at USB-C speeds, but most often connecting at USB 2.0 speeds. And on my 2023 Mac Pro, it has never connected at anything but USB 2.0 speeds and that’s trying half a dozen qualified cables. Clearly something is seriously broken in macOS.

Steps to reproduce:

This process could be repeated with the same results over and over:

  1. With nothing else plugged into any of the ports, plug-in the iPhone 15 Pro Max using a Thunderbolt 4 or 3 cable. It would usually connect at USB 2.0 speeds. Then it flipped to USB 3 10 Gbps for no apparent reason. It seems to come in "runs" of either/or. For the longest time it was USB 2.0 and rebooting, etc had no effect.
  2. Plug in a peripheral like the OWC Atlas FXR; FXR will connect at USB 2.0 speeds regardless of iPhone connectivity speed (two samples of FXR, multiple qualified cables used).
  3. Unplug the iPhone; the FXR now renegotiates at full speed (no unplug/replug involved).
  4. Plug the iPhone in again; the FXR remains at TB speed.

None of this makes any sense in the context of 3 independent Thunderbolt busses of the 2021 MacBook Pro M1 Max. Clearly it is a nasty macOS bug.

Issues like this should not surprise: in macOS Ventura, Apple broke Personal Hotspot and Apple broke Bluetooth and Apple broke command key shortcuts in Terminal. And a lot more. Apple quality control is rotten to the core.

Related findings:

  • A brand-new OWC Atlas FXR and cable make no difference. It is not an FXR-sample issue.
  • iPhone 15 Pro Max randomly sees USB 2.0 480 Gbps or USB 3 10 GBps with no apparent rhyme or reason. It seems to get “stuck” on one speed with repeated tests, then flip and get stuck at the other speed.
  • Plugging in the FXR after the iPhone results in USB 2.0 speeds, regardless of the iPhone connection speed. No exceptions seen. Plugging the FXR in first and it always runs at full speed.
  • Unplugging the iPhone resets the FXR to full speed without unplugging/replugging.

For weeks, the iPhone 15 Pro Max would only connect at USB 2.0 speeds. Then it finally started connecting at 10 Gbps/sec... and then reverting to 480 Mbps—flaky and random but tending to run in streaks of either/or.

Product ID:	0x12a8
Vendor ID:	0x05ac (Apple Inc.)
Version:	16.02
Serial Number:	00008130000E20C82061401C
Speed:	Up to 10 Gb/s  (or, randomly, 480 Mbps)
Manufacturer:	Apple Inc.
Location ID:	0x00200000 / 1
Current Available (mA):	900
Current Required (mA):	896
Extra Operating Current (mA):	1500
Sleep current (mA):	2400
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