Hello @Maotom
I hope you are doing very well.
Which i.MX8MP Image are you using? (Multimedia, Full, core, etc.).
Normally, the memtool is located under /unit_tests/memtool on the i.MX BSPs.
About the registers, there are not described on the reference manual, but please follow the i.MX 6/7/8 series USB Certification Guide (AN12409).
Best regards,
Salas.