I know, it's probably a design flaw, but hear me out.
I'm designing a board with an STM32MP135 (in the form of a Myir Tech SoM). I have both USB1, and USB2 configured as USB-A / host mode. There is also an FTDI chip attached to UART4 for a console.
The problem that I'm having is that when I try to enter USB DFU mode (bootn = 0, 0, 0) it will only work if I connect through an OTG-style adapter to another USB-A port. The only way that I can get it to enumerate is if I connect USB2 (type A plug on the target) to a USB-C to A converter, and then to a USB-A port on the laptop. If I connect USB-A on the target to USB-C on the laptop it does not enumerate at all and if I connect via a powered HUB it gets stuck in some sort of enumeration loop.
This is the first board revision and I did not expect to need USB-OTG so those pins are floating, which I'm guessing is what I've missed, but I can't find where it mentions how they are used in the documentation. I don't have any use for USB-OTG otherwise. So my question is what is the expected setup? Why is it being fussy about cables, ports, and connectors? Would the FTDI chip be interfering somehow?
(also other features of the board work fine, and when it does enumerate properly I can flash firmware without a problem, and there does not seem to be any issue with USB host mode. So while it could certainly be poor design I'm not seeing signs of problems otherwise.)
Thanks for any advice you can offer.
