@Tim Edwards Do we have any data on maximum frequency operation for caravel Riscv + Subsystem in CI2306Q ? Is there is any improvement in Caravel PLL and what will be it's stable working frequency range.

I believe that the processor is rated for 40MHz operation and this is unchanged since the VexRISC was introduced. Not sure what you mean by "improvement" in the PLL (by which I assume you mean the DLL), as it works as designed. With the 10MHz clock on the board, the working range of the DLL oscillator is 50 to 113 MHz, so the output range is 5.5MHz to 113MHz.