The Coprocessor Data Processing (CDP) instruction is used for coprocessor instructions that do not operate on values in ARM registers or in main memory. One example is a floating-point multiply instruction for a floating-point accelerator processor.

To enable coprocessors to continue execution of CDP instructions while the ARM9E-S core pipeline is stalled (for instance while waiting for an AHB transfer to complete), the coprocessor receives the free-running system clock CLK, and a clock enable signal CPCLKEN. If CPCLKEN is LOW around the rising edge of CLK then the ARM9E-S core pipeline is stalled and the coprocessor pipeline follower must not advance.

This prevents any new instructions entering Execute within the coprocessor but enables a CDP instruction in Execute to continue execution. The coprocessor is only stalled when the current instruction leaves Execute and new instructions are required from the ARM946E-S interface.This goes some way towards decoupling the external coprocessor from the ARM9E-S memory interface.

There are three classes of coprocessor instructions:

Examples of how a coprocessor executes these instruction classes are given in the following sections: