Allen,
The basic functionality of a PRD is equivalent to a continous or periodic Clock instance in BIOS 6.x.
There are some differences though, like PRD runs at SWI level in BIOS 5.x but Clocks run a Hwi level in BIOS 6.x.
I think your PRD objects should become Clock objects.
So in your app where are you calling PRD_tick from?
Judah