Problem in Interrupt for USB device

Hi,
 I added basic functionality in bootloader(eboot.nb0)for downloading
Nk.nb0  through USB. I am working in wince for ln2440sbc board.
I registered for Interrupt service routine in my bootloader like this.
pISR=((unsigned)EA000000+((unsigned)IsrHandler -(8c000000-18-8)>>2)
and my pISR is *((unsigned *)(0x30000000+0x18))
(Since 8c000000 is mapped to 0x30000000.)
IsrHandler is in assembly code and I am calling Isrusbd function from
assembly itself.
I Isrusbd i included reconfiguring USB device and other
functionalities of it.

My program control is not transferred to Isrusbd device itself

I think interrupt didn't come for USB device.
How I have to find out and trace for it...
I tried i didn't get interrupt for USB device.
Anything for interrupt i have to include in startup.s for interrupt
routine.

Regards,
Kirthika.