[ixp1200] Timer in IXP1200EB

Hello All, Has anybody tried to program the timer in IXP1200? I currently have VxWorks running on it. I am trying to use Timer 4 for my application, but control is not reaching my ISR. I believe I have done everything as mentioned in the programmer's guide. I have enabled the IXP1200_IRQSTATUS, but it still doesnt work. Can anybody tell me what step I could be missing. Thanks, Sandeep.