CCS/TMS320F28069: F28069 usb_bulk application ILLEGAL_ISR issue

Tool/software: Code Composer Studio

I am developing a USB application on 28069PFP

I copied the usb_dev_bulk example code into my application.

I compiled it with RAM_lnk.cmd and run. It died.

So I step into here

it goes into USBOTGMode()

when I continue to step over, it goes to ILLEGAL_ISR and stays in ILLEGAL_ISR and USER1_ISR

But it does set the SOFTCONN bit and "Unknown device" displayed

Can anyone give me some advice on this? what might be the problem? How to debug this?

Thanks