这是ti官网的一个例子片段
void InitPll(Uint16 val, Uint16 divsel)
{
// Make sure the PLL is not running in limp mode
if (SysCtrlRegs.PLLSTS.bit.MCLKSTS != 0)
{
// Missing external clock has been detected
// Replace this line with a call to an appropriate
// SystemShutdown(); function.
asm(" ESTOP0");
}
// DIVSEL MUST be 0 before PLLCR can be changed from
// 0x0000. It is set to 0 by an external reset XRSn
// This puts us in 1/4
if (SysCtrlRegs.PLLSTS.bit.DIVSEL != 0)
{
EALLOW;
SysCtrlRegs.PLLSTS.bit.DIVSEL = 0;
EDIS;
}
// Change the PLLCR
if (SysCtrlRegs.PLLCR.bit.DIV != val)
{
EALLOW;
// Before setting PLLCR turn off missing clock detect logic
SysCtrlRegs.PLLSTS.bit.MCLKOFF = 1;
SysCtrlRegs.PLLCR.bit.DIV = val;
EDIS;
// Optional: Wait for PLL to lock.
// During this time the CPU will switch to OSCCLK/2 until
// the PLL is stable. Once the PLL is stable the CPU will
// switch to the new PLL value.
//
// This time-to-lock is monitored by a PLL lock counter.
//
// Code is not required to sit and wait for the PLL to lock.
// However, if the code does anything that is timing critical,
// and requires the correct clock be locked, then it is best to
// wait until this switching has completed.
// Wait for the PLL lock bit to be set.
// The watchdog should be disabled before this loop, or fed within
// the loop via ServiceDog().
// Uncomment to disable the watchdog
DisableDog();
while(SysCtrlRegs.PLLSTS.bit.PLLLOCKS != 1)
{
// Uncomment to service the watchdog
// ServiceDog();
}
EALLOW;
SysCtrlRegs.PLLSTS.bit.MCLKOFF = 0;
EDIS;
}
// If switching to 1/2
if((divsel == 1)||(divsel == 2))
{
EALLOW;
SysCtrlRegs.PLLSTS.bit.DIVSEL = divsel;
EDIS;
}
// If switching to 1/1
// * First go to 1/2 and let the power settle
// The time required will depend on the system, this is only an example
// * Then switch to 1/1
if(divsel == 3)
{
EALLOW;
SysCtrlRegs.PLLSTS.bit.DIVSEL = 2;
DELAY_US(50L);
SysCtrlRegs.PLLSTS.bit.DIVSEL = 3;
EDIS;
}
}
从程序来看分频倍频由val divsel这两个变量决定，我在外部用30MHZ晶振，应选取10倍频，2分频，那这两个值需要在头文件分别定义为10和2，但是官方程序的头文件2833x_example.这样写的//#define DSP28_DIVSEL 0 // Enable /4 for SYSCLKOUT
//#define DSP28_DIVSEL 1 // Disable /4 for SYSCKOUT
#define DSP28_DIVSEL 2 // Enable /2 for SYSCLKOUT
//#define DSP28_DIVSEL 3 // Enable /1 for SYSCLKOUT
#define DSP28_PLLCR 10
//#define DSP28_PLLCR 9
//#define DSP28_PLLCR 8
//#define DSP28_PLLCR 7
//#define DSP28_PLLCR 6
//#define DSP28_PLLCR 5
//#define DSP28_PLLCR 4
//#define DSP28_PLLCR 3
//#define DSP28_PLLCR 2
//#define DSP28_PLLCR 1
//#define DSP28_PLLCR 0 /
意思是让我们从中各选择一个，其它的宏定义删掉，但是程序中是val divsel这两个值对寄存器赋值，而不是DSP28_DIVSEL 和DSP28_PLLCR，我是否应该改成/#define divsel 2和#define val 10？ |
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