[Teensy 3.1] Reset while reading USB related registers...

Hello,

Sorry for any dumb question.... I'm learning...

I try to read the USB registers content (USB0_USBTRC0, USB0_BDTPAGE1....) and it makes the teensy to reboot so I'd like to know :

- How to write an simple exception handler to get the reason ? Should I implement an handler to the Fault vectors ? (0x0000_0014,...) ? If yes, is there any example somewhere ?
- Why reading the registers make the teensy rebooting ? Is it a supervisor issue ?
- How to enter in spv mode ? (if relevant..)

Thanks in advance !

shazz

ok partially solved.... USB registers cannot be read before USB Clock Gate Control is enabled in SIM_SCGC4...

by the way, I'll still be happy to get a nice exception handler