I’m not sure I understand the question, but are you asking how to use the micro-OTG port in devie mode as a custom device? If this is the case, then you’d want to check out the Linux kerne’s “gadget” framework. I have not yet looked at it, but I believe in R28.2 the OTG port does have some device mode function assigned to it, whereas in earlier releases this would not be the case.