The CPU has control over access to the RCP. The RSP and RDP portions of the RCP can be used individually, or as a group. The CPU creates a task list that specifies what microcode to run and what command list to execute. The task is then run on the RSP.
There are OS commands to start the task and to end (i.e., preempt) a task. The RDP usually receives graphics rendering commands directly from the RSP. However, it is also possible to drive the RDP from a list that is in DRAM.