F28335 GPIO OUTPUT PLUS PROBLEM

Hi~

Recently i used the pin GPIO33 of F28335 to send a plus, the program copied from controlSUITE gpio_setup.c and  add simple line :

while(1){

GpioDataRegs.GPBSET.bit.GPIO33=1;

GpioDataRegs.GPBCLEAR.bit.GPIO33 =1;

}

I configed the clock of CPU had up to 150Mhz and the plus width should be 6.67ns*2 per cycle, while through my oscilloscope it's about 100ns per cycle,  has somebody meet similar problem or just give me some suggestions?

Thanks！