1. 硬件上连接晶振
2. 软件上在systemctrl.c中,改成下面的
//---------------------------------------------------------------------------
// Example: XtalOscSel:
//---------------------------------------------------------------------------
// This function switches to External CRYSTAL oscillator and turns off all other clock
// sources to minimize power consumption. This option may not be available on all
// device packages
void XtalOscSel (void) {
EALLOW;
SysCtrlRegs.CLKCTL.bit.XTALOSCOFF = 0; // Turn on XTALOSC
SysCtrlRegs.CLKCTL.bit.XCLKINOFF = 1; // Turn off XCLKIN
SysCtrlRegs.CLKCTL.bit.OSCCLKSRC2SEL = 0; // Switch to external clock
SysCtrlRegs.CLKCTL.bit.OSCCLKSRCSEL = 1; // Switch from INTOSC1 to INTOSC2/ext clk
SysCtrlRegs.CLKCTL.bit.WDCLKSRCSEL = 1; // Switch Watchdog Clk Src to external clock
SysCtrlRegs.CLKCTL.bit.INTOSC2OFF = 1; // Turn off INTOSC2
SysCtrlRegs.CLKCTL.bit.INTOSC1OFF = 1; // Turn off INTOSC1
EDIS;