The ZPU is designed to use as few FPGA resources as possible. So if you're looking for something to just do a little bit of control logic to tie things together

The ZPU is designed to use as few FPGA resources as possible. So if you're looking for something to just do a little bit of control logic to tie things together, it probably is the way to go. Rocket on the other hand is a full-fledged in-order core with hardware mutliplier, single-precision and double-precision floating-point units, and MMU. Therefore, it can do things like boot a full Linux kernel, which the ZPU cannot. Rocket also has the RoCC co-processor interface, which allows you to define your own ISA extensions in Chisel.