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12. CPU control registers (CCRs)

Modern CPUs have a plethora of special registers, used to control various features such as performance monitoring, virtual memory, cache control, timestamp counters/timers, etc. The F-CPU architecture is no exception, but it innovates in that there is a single, standard mechanism for accessing such registers that is at once fast, secure and simple to implement. In the F-CPU architecture, all CPU control registers are mapped in the first half (32KB) of the special coprocessor address space. Moving a value between any CCR and any virtual register takes a single instruction which executes in a single clock cycle.

The CCRs are only accessible in supervisor mode. Trying to access a CCR in user mode results in an illegal instruction exception.


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