使用内部HF振荡器，SYSCLK倍频到48MHz，USBCLK也为48MHz-use internal oscillator, then the SYSCLK frequency of 48MHz, USBCLK for 48 MHz

ofdm系统的仿真实现 加入导频 训练序列 小数倍频偏估计-Join ofdm system simulation pilot training sequence to achieve a small multiple of the frequency offset estimate