USB Accessory Device Charging Behavior Changed with iOS18

App & System Services Drivers
nares OP
Created 3d
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Hello,

We are experiencing some issues with our USB accessory unexpectedly charging the iOS device it is connected with only when the iOS device supports USB-C and is on iOS 18+

The following is a description of the discrepancy we note between iOS versions:

  • After performing a USB Role switch, our Accessory becomes a typical USB Device and the Apple device becomes the USB host.

with iOS 17: 


  • The Accessory then sends a PowerSourceUpdate message to the iOS 17 device via iAP2 protocol. Apple device has a USB Type C Connector. *

  • We are specifying:

  1. AvailableCurrentForDevice = 0 mA 
  2. DeviceBatteryShouldChargeIfPowerIsPresent = 1.
  • Three observations:
  1. iPad Battery Settings page -  we observe  'Last charged to…' (indicating no charging)
  2. On the Lumify App running (iOS 17), we observe that UIKit.current.batteryState indicated 'Not charging'
  3. Battery icon on top right of the screen indicates 'No Charging'

with iOS 18:

  • The same Accessory sends the same PowerSourceUpdate message to the iOS 18 device via iAP2 protocol using USB Type C Connector.

  • We are specifying the same:

  1. AvailableCurrentForDevice = 0 mA
  2. DeviceBatteryShouldChargeIfPowerIsPresent = 1.
  • We observe:
  1. iPad Battery Settings page -  we observe  'Charging' 
  2. On the Lumify App running (iOS 18), we observe that UIKit.current.batteryState indicated 'Charging'
  3. Battery icon on top right of the screen indicates 'No Charging'

Please could you help us understand why the Battery status is showing as 'Charging' in the Settings page and with the 'UIKit.current.batteryState' even though we have specified 'AvailableCurrentForDevice = 0 mA'?


Since our accessory is heavily reliant on the Battery status / Charging state, is there potentially another way we get an accurate battery charging status that we are missing? Or are there other suggestions outside of what we do currently to ensure our accessory does not place the iOS18 device into a charging state?

Replies  2
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DTS Engineer OP
Apple
3d

So, three points here:

  1. The MFi program has its own support process, which you can find more information on in the "MFi Portal Technical Support" section of the MFi Licensing Handbook on the MFi portal. I have one brief comment (see below), but a more detailed investigation should go through that process.

  2. Regardless of what you find (see below), please file a bug on this and then post that number back here. Something is obviously wrong here and we should correct that.

  3. Has anything actually changed in terms of what's actually happening on the USB bus? If actual bus behavior hasn't changed, then I think this is basically just a bug. Note that the main reason split behavior like this happen:

  1. iPad Battery Settings page - we observe 'Charging'
  2. On the Lumify App running (iOS 18), we observe that UIKit.current.batteryState indicated 'Charging'

Versus:

  1. Battery icon on top right of the screen indicates 'No Charging'

...is that the first two case are pulling from one API and the second case is pulling from a different (typically lower level) API.

In any case, the first thing to sort out here is whether there's been an actually behavior change here (and the battery indicator is wrong) or whether UIKit.current.batteryState is just returning the wrong value.

__
Kevin Elliott
DTS Engineer, CoreOS/Hardware

0
nares OP
16h

Thank you Kevin for this detailed response!

I have submitted an MFI DTS ticket now. It has the case ID: (Case-ID: 12584819)

I am additionally going to file a bug as you suggested as well and am just gathering all the needed information for that (mainly getting a good sysdiagnose log to include there). I will update here with the number for this issue once I have it submitted as well.

As far as anything changing in terms of USB bus behavior, It should be untouched since the time of the initial accessory development so I suppose this leans more towards the bug potential.

We have some further info after measuring the current flowing into the iOS device in both cases as well:

Conditions: On Boot up PowerSourceUpdate msg sent by LPM to iPad -> AvailableCurrentForDevice = 0 mA

iOS 17 Ipad Battery Level 31 PowerUpdate message parameters sent by iPad to LPM MaximumCurrentDrawnFromAccessory 0 DeviceBatteryWillChargeIfPowerIsPresent 0 IsExternalChargerConnected 0 BatteryChargingState 1 BatteryChargeLevel 30 Current measured at Connector 420 mA -> 0 mA

iOS 18 Ipad Battery Level 46 PowerUpdate message parameters sent by iPad to LPM MaximumCurrentDrawnFromAccessory 0 DeviceBatteryWillChargeIfPowerIsPresent 0 IsExternalChargerConnected 0 BatteryChargingState 1 BatteryChargeLevel 45 Current measured at Connector 420 mA -> Persists at 420mA

I'll be sure to include this above information in that new bug when it is written as well.

Thank you, Nick

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USB Accessory Device Charging Behavior Changed with iOS18
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