A processor clock control device operable to control a plurality of clock signals output to a processor, said processor comprising a plurality of domains each clocked by a respective one of said plurality of clock signals, said processor being operable in different modes including a functional mode and a test mode, said processor clock control device comprising: a clock signal input operable to receive a slower reference clock signal or a higher speed operational clock signal; at least two clock signal outputs each operable to output a clock signal to a respective domain of said processor; a mode control signal input operable to receive a mode control signal indicating a mode of operation of said processor; a launch control signal input operable to receive a launch control signal, said launch control signal indicating portions of said processor to be tested; and an initiation signal input operable to receive an initiation signal indicating initiation of a processor test; wherein said processor clock control device is operable: in response to receipt of a test mode signal at said mode control signal input to receive a reference clock at said clock signal input and to output said reference clock at at least one of said plurality of clock signal outputs; and in response to a predetermined launch control signal received at said launch control signal input, said predetermined launch control signal indicating testing of a path between one of said clocked domains clocked by one of said clock signal outputs and one other of said clocked domains clocked by one other of said clock signal outputs, and following receipt of said initiation signal, to independently control said plurality of clock signal outputs such that at least one launch clock pulse is output from said one of said clock signal outputs while said one other of said clock signal outputs is suppressed, and following this to output at least one capture clock pulse from said one other of said clock signal outputs while said one of said plurality of clock signal outputs is suppressed.