MSP430F1611: Changing timer_a source does not work

shadowfax47

Part Number: MSP430F1611

I am using Timer_A in compare mode to generate PWM output on my MSP430f1xx. During Osc failure, I am changing Timer_A source from SMCLK to ACLK (XTS=1).

ACLK now runs on the same frequency as SMCLK did, and all the Timer registers look ok. But the PWM output frequency is now random (which i assume is because Timer_A is not running on ACLK as intended).

Here is my NMI routine,

#pragma vector=NMI_VECTOR
__interrupt void nmi_ (void)
{
if (OFIFG) {
configure_lfxt1(); // Ok
IFG1 &= ~NMIIFG;
IFG1 &= ~OFIFG;
IE1 |= NMIIE;

TACTL &= ~(MC0 | MC1);
TACTL &= ~TASSEL_2;
TACTL |= TASSEL_1;
__delay_cycles(200);
TACTL |= MC_1;
}

Any pointers would be appreciated. Thanks,

over 8 years ago

0 Caleb Overbay over 8 years ago

TI__Genius 15370 points

Hi,

Just so I understand your application, you have an external source(XT2) feeding SMCLK and when you get an oscillator fault you want to switch to a separate external source(LFXT1) for Timer A?

The code snippet you've posted above looks good to me. I suspect this is an issue where the ACLK is not operating at the frequency you think it is or it hasn't been configured properly. Have you tried outputting the value of ACLK to a pin and checking that you are getting the frequency you expect?

Best regards,
Caleb Overbay

0 shadowfax47 over 8 years ago in reply to Caleb Overbay

Prodigy 240 points

Hi Caleb,

You understood the scenario right. Yes I did try to output the ACLK frequency and it is clocking as expected (The other applications which switch to ACLK, run without any issues).

Also, the reason I switch to ACLK from SMCLK is because I cannot configure SMCLK with LFXT1 (XTS=1).

Here's how I switch from XT2 to LFXT1.

BCSCTL1 |= XT2OFF + XTS + DIVA_2;
__delay_cycles(2000); // Wait for Osc to kick in
BCSCTL2 |= SELM_3 + DIVM_1 + SELS + DIVS_2;

Best Regards,

0 Caleb Overbay over 8 years ago in reply to shadowfax47

TI__Genius 15370 points

Hi,

Everything I see so far looks correct. Could you try running Timer-A off the ACLK from the beginning and see if you get the same results? By doing this, we can narrow whether the issue is in the code when switching from SMCLK to ACLK or if there is something wrong with running Timer-A from ACLK.

Best regards,
Caleb Overbay

0 Tony Philipsson over 8 years ago in reply to shadowfax47

Guru 12050 points

BCSCTL2 |=
ORing placeholder-values may produce incorrect settings depending on what prevoius bit already set.

0 MichRFT over 8 years ago in reply to Tony Philipsson

Expert 2110 points

A clear during configuration change could help?

0 Bruce McKenney over 8 years ago

Guru 99455 points

> if (OFIFG) {
Since OFIFG is a constant, this is always true.

> IE1 |= NMIIE;
See also: "Note:" about setting NMIIE in the ISR at the end of SLAU049F section 2.2.1 (notwithstanding the prior text which seems to say exactly the opposite).

0 shadowfax47 over 8 years ago in reply to Tony Philipsson

Prodigy 240 points

This works as expected with both MCLK and ACLK clocking desired frequencies.

0 shadowfax47 over 8 years ago in reply to Bruce McKenney

Prodigy 240 points

Regarding the OFIFG you are right, I modified the code.

But regarding setting NMIIE, I am not sure which part of the note you are referring to. I am not holding RST/NMI low or am I modifying NMI edge select bit.

0 shadowfax47 over 8 years ago in reply to Caleb Overbay

Prodigy 240 points

Hi,

I ran Timer_A off the ACLK from the beginning as suggested and noticed that the it still fails.
Basically, TASSEL is having no effect on Timer_A. Irrespective of what source is selected, it always chooses SMCLK.
Any idea why this happens?

Best Regards

0 Caleb Overbay over 8 years ago in reply to shadowfax47

TI__Genius 15370 points

Hi,

Can you post code that we can use to try to replicate this issue? I'd like to try this out on my end.

Best regards,
Caleb Overbay

0 Caleb Overbay over 8 years ago in reply to shadowfax47

TI__Genius 15370 points

Hi,

Do you still need help with this issue or do you have any progress you'd like to share?

Best regards,
Caleb Overbay

0 shadowfax47 over 8 years ago in reply to Caleb Overbay

Prodigy 240 points

This issue is solved. The problem as imagined was because Timer_A was not switching to ACLK at all. There was a bug in the code.

0 Caleb Overbay over 8 years ago in reply to shadowfax47

TI__Genius 15370 points

Hi,

That's good to hear. I hope you don't mind me prying a little further, but where was the bug in the code?

Best regards,
Caleb Overbay

0 shadowfax47 over 8 years ago in reply to Caleb Overbay

Prodigy 240 points

Sure Caleb, one of the functions was assigning a value to TACTL register thereby modifying TASSELx (instead of ORing relevant bits) which i completely overlooked.

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MSP430F1611: Changing timer_a source does not work