Register Transfer Activity In a simple architecture(not considering parallel architecture) how exactly this can be performed in a single clock cycle:
P:R1 &lt;- R2, R2 &lt;-R1
where R1 and R2 are registers and P is a control variable.

I do not exactly understand when does this microoperation gets completed on the rising edge of the beginning of the cycle or just before clock transition.
One way this can be performed in a single cycle is through register renaming.  If the processor supports register renaming, no data needs to be moved: one simply renames which register is called R1 and which one is called R2.

If the processor doesn't support register renaming, the other option is that the data can simply be swapped between the two registers.