I'm using MPC5777c and setup clock speed of core 0 to be 264Mhz, which I've tested via measuring the ENGCLK on evaluation board. Then I try to test the actual main loop performance. But when I toggle a pin inside main loop and measure the pin using oscilloscope, the frequency only around 1.4 MHz, which is pretty slower compared with its core clock. I've checked that my main loop only contains like 5 instructions (write 1 to a pin, write 0 to a pin, that's all), and it doesn't contain anything else. The activation of cache doesn't cause any change of this.