#define DELAY_US(A) DSP28x_usDelay(((((long double) A * 1000.0L) / (long double)CPU_RATE) - 9.0L) / 5.0L)
中
A对应需要延迟的时间，单位是us，L代表ns
CPU clock speed 代表主频即SYSCLKOUT
而 CPU_RATE是CPU clock speed的倒数
如
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| Specify the clock rate of the CPU (SYSCLKOUT) in nS.
Take into account the input clock frequency and the PLL multiplier
selected in step 1.
Use one of the values provided, or define your own.
The trailing L is required tells the compiler to treat
the number as a 64-bit value.
Only one statement should be uncommented.
Example 1:150 MHz devices:
CLKIN is a 30MHz crystal.
In step 1 the user specified PLLCR = 0xA for a
150Mhz CPU clock (SYSCLKOUT = 150MHz).
In this case, the CPU_RATE will be 6.667L
Uncomment the line: #define CPU_RATE 6.667L
Example 2: 100 MHz devices:
CLKIN is a 20MHz crystal.
In step 1 the user specified PLLCR = 0xA for a
100Mhz CPU clock (SYSCLKOUT = 100MHz).
In this case, the CPU_RATE will be 10.000L
Uncomment the line: #define CPU_RATE 10.000L
-----------------------------------------------------------------------------*/
#define CPU_RATE 6.667L // for a 150MHz CPU clock speed (SYSCLKOUT)
//#define CPU_RATE 7.143L // for a 140MHz CPU clock speed (SYSCLKOUT)
//#define CPU_RATE 8.333L // for a 120MHz CPU clock speed (SYSCLKOUT)
//#define CPU_RATE 10.000L // for a 100MHz CPU clock speed (SYSCLKOUT)
//#define CPU_RATE 13.330L // for a 75MHz CPU clock speed (SYSCLKOUT)
//#define CPU_RATE 20.000L // for a 50MHz CPU clock speed (SYSCLKOUT)
//#define CPU_RATE 33.333L // for a 30MHz CPU clock speed (SYSCLKOUT)
//#define CPU_RATE 41.667L // for a 24MHz CPU clock speed (SYSCLKOUT)
//#define CPU_RATE 50.000L // for a 20MHz CPU clock speed (SYSCLKOUT)
//#define CPU_RATE 66.667L // for a 15MHz CPU clock speed (SYSCLKOUT)
//#define CPU_RATE 100.000L // for a 10MHz CPU clock speed (SYSCLKOUT)
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