MSP430F5510: Using HW timers to do an efficient blocking delay

Jordi Armengol

Prodigy 10 points

Part Number: MSP430F5510

Hello,

I am trying to do an efficient blocking delay for my university project. What i have right now working:

volatile int32_t counter;

void timers_init(void) {

TA0CTL |= TASSEL__SMCLK | MC__UP;
TA0CCR0 = 16000; //SMCLK is 16MHz so this way we count to 1 ms every interrupt

}

void wait_ms(uint32_t delay) {

counter = delay;
TA0CTL |= TACLR;
TA0CCTL0 |= CCIE;

__bis_SR_register(LPM0_bits + GIE);
while(counter > 0);

}

#pragma vector=TIMER0_A0_VECTOR
__interrupt void timer0_A0_ISR(void) {

--counter;
if (counter == 0) {

__bic_SR_register_on_exit(LPM0_bits);
TA0CCTL0 &= ~(CCIE);

}

TA0CCTL0 &= ~(TA0IV_TA0IFG);

}

Is there any way to make it more efficient? The precision of the delay is not a priority but i don't want to settle by only "it's working"

Any help will be appreciated!

over 7 years ago

0 Bruce McKenney over 7 years ago

Guru 103195 points

I'm not sure the "efficient" is a major concern when you're spending almost all of your time waiting in LPM, but I do see some holes:
-----------------------
> TA0CCTL0 &= ~(TA0IV_TA0IFG);

If the goal here was to clear TA0CCTL0:CCIFG, then (1) this doesn't do it and (2) you don't need to do it since TA0CCTL0:CCIFG (specifically) auto-clears when you take the interrupt. I suspect you should just remove this line.
-----------------------
> __bis_SR_register(LPM0_bits + GIE);
>while(counter > 0);

If you believe that the (only possible) wakeup happens when counter==0, then the second line is unnecessary. If you think some other entity in your program might also do a wakeup, it should probably look more like:

>while(counter > 0)
> __bis_SR_register(LPM0_bits + GIE);

(For that matter, if there are multiple wakeup agents in the program, I would probably make this more fail-safe by moving the clearing of CCIE from the ISR to here, so the ISR just keeps issuing wakeups -- typically only one -- until this code recognizes it.)
-----------------------
>volatile int32_t counter;

A 32-bit variable can't be atomically fetched/stored. If you can't use an int16_t (32+ seconds), you should disable interrupts around the fetches and stores.

0 Wei.Jetim Zhao over 7 years ago

TI__Genius 13215 points

Hi Jordi,

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MSP430F5510: Using HW timers to do an efficient blocking delay