USB snooping tools

Suggestions for good USB snooping tools. The AppleTV has an IR Controller located on an internal USB bus. This IR Controller also handles front panel LED control, Fan control and boot counts. Normally these type of functions are handled by applesmc but the AppleTV does not have SMC, AppleSMC is just a stub.

I'm tired of the blinking LED under linux boot and would like to also be able to control the internal fan so I need to snoop the USB bus to trap and decode transactions/message content. Thus the need for USB snooping tools. Any suggestions?

Thanks