Accurate software delay method in IAR FOR AVR

Note: __delay_cycles(x), x must be a constant or a constant expression. If it is a variable, the compiler will report an error!

Delay functions are often used when using microcontrollers, and 430 is no exception. Common forms are:
void delay(unsigned int ms)
{
unsigned int i,j;

for( i=0;i
for(j=0;j<1141;j++); //8MHz crystal oscillator
}

Copy code //The above program segment can be used in situations where the delay accuracy is not required.

However, in the IAR software 430 compiler, we can use its internal delay subroutine to achieve the high-precision software delay we want. The method is as follows:

(1): Copy the following code to your .C source file.

#define CPU_F ((double)8000000)
#define delay_us(x) __delay_cycles((long)(CPU_F*(double)x/1000000.0))
#define delay_ms(x) __delay_cycles((long)(CPU_F*(double)x/1000.0))

Copy code (2): Modify

the #define CPU_F ((double)8000000) statement. Change 8000000 to the main frequency of your current MSP430 CPU, that is, the MCLK of the CPU.

The unit is Hz. In this example, 8000000 means MCLK=8MHZ.

(3): Usage example

delay_us(1); //1 microsecond delay

delay_ms(1); //1 millisecond delay

delay_us(3.5); //3.5 microsecond

delay delay_ms(3.5); //3.5 millisecond delay

delay_ms(1000); //delay 1 second

reason:

__delay_cycles() is a compiler system "function" and will be replaced with the corresponding loop code when IAR is compiled.

Look at the picture, the instruction (clock) cycle delay of 100 is required, and after compilation, it is exactly 100 cycles.

The result is: (1+2)*33 + 1 = 100