A computer system includes a processor, a submodule connected to the processor, an external access monitor configured to monitor a data transfer between the processor and the submodule, and a synchronization/desynchronization controller configured to synchronize or desynchronize the clock of the processor with respect to the clock of the submodule, depending on the result of the monitoring. Specifically, the processor clock is synchronized to the submodule clock when the frequency of access to the submodule by the processor is high, and the processor clock is desynchronized with respect to the submodule clock when the access frequency is low.