reTerminal DM — RAK4631-based module (mPCIe, USB variant) never enumerates in LTE/4G slot; confirmed-good module works instantly via external USB

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Hi,

I’m trying to use a RAK19713 (mPCIe-format RAK4630/RAK4631 core module) in the reTerminal DM’s 4G/LTE-designated mPCIe slot. It never appears on USB at all, with symptoms I’ve fully isolated to that slot rather than the module or host:

What works:

  • The RAK19713’s bootloader was flashed successfully via SWD (RAKDAP1, pyocd) — confirmed good.
  • Application firmware (Arduino/PlatformIO, rak4630 board target) builds and flashes successfully via UF2 drag-and-drop while the module sits in the LTE mPCIe slot — mass-storage enumeration (sd 0:0:0:0: [sda] ... Adafruit nRF UF2) works every time.
  • The same module, plugged into an external USB-A port on the same reTerminal, enumerates instantly and correctly as 239a:8029 Adafruit WisCore RAK4631 Board, with a working CDC-ACM serial interface and firmware running correctly.

What doesn’t work:

  • With the module seated in the LTE mPCIe slot, lsusb shows nothing at 239a:*, and dmesg shows zero USB/xHCI enumeration attempts for that slot at all — not a failed enumeration, just complete silence. This is consistent across two full power cycles and a physical reseat.
  • Only USB (CDC-ACM/mass-storage) is affected — SWD-based flashing to the same module while in that slot works fine, since it doesn’t depend on the slot’s USB routing.

What I suspect, from your own reTerminal DM manual’s block diagram (section 2.1.4): the legend shows a “Wi-Fi Toggle Switch” sitting between USB HUB2, the onboard WiFi module, and the Mini PCIe USB path, controlled via a GPIO expansion IC (PCA9535, I2C 0x21). This suggests the LTE slot’s USB lines may share a hub port with onboard WiFi through a switch that isn’t currently routed to the mPCIe slot, rather than the slot being an independent always-on USB path.

Question: is there a documented way (dtoverlay, script, or direct I2C write to the PCA9535) to route USB to the LTE mPCIe slot? /boot/firmware/config.txt has no relevant dtoverlay lines by default, and I haven’t found this documented in the Hardware Guide or Getting Started wiki pages.

For context, I found a related (unresolved) report on a different reTerminal model with a similar “4G module disappears after installing reTerminal drivers” symptom: [link to that forum thread]. Wondering if this is the same underlying mux/driver interaction.

Happy to provide lsusb/dmesg output, OS version, or anything else that’d help.

Thanks,
Troy (drafted by Claude)