We are experiencing problems with the USB port on iPad Pro 11 inch (M4) model number MVW13NF/A. Our custom peripheral device (based on Raspberry Pi Pico + tinyUSB stack, is configured as a network adapter class and has communication with our App over UDP protocol. Our device also acts as a DHCP server, providing the IP address for iPad.
The problem can be described as a “bus stall” or "bus hold" after sleep mode. To reproduce it we just send the iPad into sleep mode using a power button, the USB bus on M4 goes to the suspended state and won’t resume anymore when we wake the iPad up.
The problem has occurred since the upgrade to iOS 18.2.1 and has not been observed before on the previously installed iOS 17 on the same iPad Pro M4.
Also, the problem does not happen on the iPad Pro 11 inch (3rd gen with M1) model number MHW73FD/A, with the same iOS 18.2.1 installed. The problem also does not arise, if we connect our device via USB hub to the same iPad Pro M4.
We have tested different versions of tinyUSB stack (either included in RPi Pico SDK or native unpatched). The problem is independent of the library version. It occurs always if our device is connected directly to the USB port of iPad Pro (M4) with iOS 18. It also stays after upgrading to the latest iOS 18.3 (beta)
In the attached logs is (reduced for clarity) debug output from tinyUSB library about events on the USB bus. These logs were captured via RTT debugging output, using Segger J-Link debugger, so logging process does not affect the timings on the USB bus.
There are three logs attached, for cases 1: "iPad Pro M4 + iOS18" (i.e. problematic case), 2: "iPad Pro M1 + iOS18", and 3: "iPad Pro M4 + iOS18 + external USB hub" (they are non-problematic cases).
case1_usbd_log.txt
case2_usbd_log.txt
case3_usbd_log.txt
This was already posted as feedback with id FB16366509