P33M

Do you have a minimal python script that will run on a basic Pi OS install that stimulates the ring expansion?

Modbus RTU is just a framed serial protocol. I doubt the actual messages matter, just the fact that bytes are being received by the UART. If you have two rs-485...

It must be something specific in how the FTDI driver is manipulating its URBs. RS232-mode FTDI serial converters don't have this issue, or at least nobody has reported that they...

The patch is entirely driver-agnostic (and mentioned earlier in the thread). This doesn't discount the possibility that there might be some other ring condition that triggers expansion that the patch...

How are the ports being used? Do you get the out-of-memory condition if a single port is used? What userspace program is accessing the ports?

The python fragment appears to be incomplete. Can you post a self-contained testcase that you know will stimulate the bug? ``` File "serial.py", line 1, in import serial File "/home/pi/serial.py",...

> `usbreset` doesn't seem to fix when applied to a single port (using 3-digit bus and device number - BBB/DDD - as argument). Would introducing a separate USB hub change...

The bug is effectively random, but only occurs immediately after a Link TRB is traversed. I get this odd condition in room_on_ring(): `xhci_hcd 0000:01:00.0: room_on_ring B num_trbs_free 248 num_trbs 1...

Spent several hours looking at trace logs and got mightily confused until I realised there's two "bugs" happening simultaneously. usb-serial submits multiple URBs for the IN endpoint and this is...

One obvious bug was in xhci_move_dequeue_past_td() where the ring state was advanced but not accounted for. With this fixed, I still get _occasional_ drops across device open/close which makes me...