The processor has three major clock domains:
High speed core clock used to clock all major processor interfaces. The Cortex-A8 processor uses only the rising edge of CLK.
CLK controls the following units within the processor:
instruction fetch unit
instruction decode unit
instruction execute unit
L2 cache unit, including AXI interface
ETM unit, not including the ATB interface
debug logic, not including the APB interface.
The instruction fetch, instruction decode, instruction execute, load/store, and L2 cache are called the core or integer core.
APB clock that controls the debug interface for the processor. PCLK is asynchronous to CLK and ATCLK. PCLK controls the debug interface and logic in the PCLK domain.
ATB clock that controls the ATB interface for the processor. ATCLK is asynchronous to CLK and PCLK. ATCLK controls the ATB interface.
You can implement PCLK and ATCLK to be synchronous to CLK. You can also implement PCLK and ATCLK to run synchronously to each other.