CCS/MSP432P401R: Explanation about MSP432P401 delay provider

Armando Ferreira

Expert 1945 points

Part Number: MSP432P401R

Tool/software: Code Composer Studio

Hello my fellows,
I have facing some dificultys to understand how to provide a delay in MSP432P401R, so, I run the MSP432 clock system at 24MHz, after this I configure my SMCLK to run at 12MHz, when I calculate the delay wich clock I should use? the 24MHz or the 12MHz clock? How can I create a delay, can give me a example.

over 5 years ago

0 Bruce McKenney over 5 years ago

Guru 99665 points

__delay_cycles generates a (CPU) spin-loop, so it implicitly uses MCLK.

>#define HZ 24000000UL // 24MHz

>__delay_cycles(HZ/4); // Spin for one-fourth of a second

0 Armando Ferreira over 5 years ago in reply to Bruce McKenney

Expert 1945 points

Hello Bruce,

Can I preforme a delay in the following way:

void init_SysTick(void){
    SysTick->CTRL = 0;              /**/ Disable SysTick durring step
    SysTick->LOAD = 0xFFFFFFFF;     /**/ Max reload value
    SysTick->VAL = 0;               /**/ Anywrite to current clears it
    SysTick->CTRL = 0x00000005;     /**/ Enable SysTick, 24MHz, no interuptions
}

/*DELAY MICROSECONDS*/
void delay_us(unsigned microseconds){
    SysTick->LOAD = (microsec * 24 - 1);
    SysTick->VAL = 0;
    while ((SysTick->CTRL & 0x00010000) == 0);
}

the "SysTick->CTRL = 0x00000005;" it gives me a big doubt because it is not clear how it works

0 Bruce McKenney over 5 years ago in reply to Armando Ferreira

Guru 99665 points

It seems that it should work. The meanings of the CTRL bits are given in TRM (SLAU356H) Table 2-54.

It's not clear to me what you gain by doing it this way. You're still doing a spin loop based on MCLK, but it's cost you the use of SysTick.

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CCS/MSP432P401R: Explanation about MSP432P401 delay provider