I just picked up a USB hub "HAT" (it actually attaches underneath, so it's more of a HAB I guess?) for my pi zero 2 W (running Ubuntu 24.04 server):
https://makerspot.com/stackable-usb-hub-for-raspberry-pi-zero/
This was pretty straightforward to attach. it interfaces via pogo pins on the bottom, and the pins appear to line up correctly with the appropriate pads on the bottom.
I power up the combined zero+hat via the hat's microUSB port and it boots as expected, so at least the power pins are working as designed.
However, the USB ports all seem to be nonfunctional. I watch dmesg when I attach known good working devices (SDR dongle, flash drive, etc) and I never see any activity. It seems that the two most likely causes are 1) bad hardware or 2) the Pi is in OTG mode (several reports in reviews about this behavior in OTG mode).
I checked a few things from this article: Debugging USB OTG Serial on the Pi Zero W
The things I checked seem to imply I am not in OTG mode and should be in USB host mode, I think. E.g.
goldeen:~ # sudo lsmod | grep g_serial
goldeen:~ # sudo dmesg | grep g_serial
goldeen:~ # ls -l /dev/ttyGS*
ls: cannot access '/dev/ttyGS*': No such file or directory
goldeen:~ # cat /boot/firmware/cmdline.txt
console=serial0,115200 multipath=off dwc_otg.lpm_enable=0 console=tty1 root=LABEL=writable rootfstype=ext4 rootwait fixrtc cfg80211.ieee80211_regdom=US
I did have dtoverlay=dwc2 in my config.txt (I commented this out and rebooted and nothing changed)
So, given all of that I believe I'm in host mode and the hub should work. But I'm not sure (it's hard to find something that definitively says "this will tell you that you're in host mode" via googling) so I'm looking for anything else to check or reconfigure. I suspect the hardware itself may be bad (seeing more than a few reports of faulty units).
