An integrated circuit chip comprising system circuitry and debugging circuitry. The system circuitry comprises a peripheral circuit. The debugging circuitry comprises a debug unit and a debug adapter. The debug unit is connected to the peripheral circuit. The debug adapter interfaces between the debug unit and a debug controller. The debug adapter is configured to receive a sequence of debug commands from the debug controller, each debug command instructing the debug unit to perform an action other than responding to a poll. In respect of each debug command, the debug adapter sends the debug command to the debug unit, and polls the debug unit to query whether the debug unit has performed the action instructed in that debug command.