MSP430FR5969: multiple interrupts set-up

Hi Brandon, 

Thank you for your prompt response. Please see the feedback from our customer.

"The response was kinda on the right path, but my question is more about how to continue processing in the main loop after starting the interrupts.

I have Timer B0 set to interrupt on at 250 Hz rate. When that interrupt occurs, that ISR merely starts a new A/D Conversion and returns. When the A/D Conversion is done, that ISR reads the value from MEM0 and puts it into an array. Originally, I was also having this ISR do all the processing of the digitized data, but I'm pretty sure there's too much to do in 1/256th of a second.

Since the bulk of the processing work only needs to be done every 1/2 sec, I have now set up Timer A0 to generate an interrupt every 0.5 seconds. Inside this ISR, my intention is to do the minimum needed with interrupts disabled, then enable interrupts and continue processing. If Timer B0 interrupts again, that's fine - it'll start another ADC cycle and then RTI; the ADC will complete & interrupt will occur & save MEM0; and I'll go back to my processing. The array is big enough to hold several seconds of samples.

At the end of the Time B0 and ADC ISR's, I have this code:
__bis_SR_register(LPM0_bits + GIE); // LPM0, ADC12_B_ISR will force exit
__no_operation(); // For debugger

If the processor goes into LPM0 but returns to the Timer A0 ISR, does it automatically come out of LPM0?
When it's OK to allow interrupts in Timer A0 ISR, how do I do that? Is it as simple as calling
__enable_interrupt();
__no_operation();"

Hi Marvin,

The TB0 interrupt vector is  higher priority than TIMA0 interrupts in this device, so this can function this way naturally, but it isn't ideal to nest* ISRs like this, as time spent in the other ISR will add to the total execution time of their TA ISR. 

They can continue in the main loop (i.e. come out of LPM0) by adding a call to the __bic_SR_register_on_exit intrinsic. Dennis provides a very good explanation of how this works in this thread: https://e2e.ti.com/support/microcontrollers/msp-low-power-microcontrollers-group/msp430/f/msp-low-power-microcontroller-forum/1016520/msp430fr2433-inquiry-about-__bis_sr_register-and-__bic_sr_register_on_exit

I feel like there is still the option of using the Timer A if they want to time when these calculations occur, just to set a flag that causes the calculations to start when you return to your main loop. If TIMB/ADC interrupt occurs during that, then you will return to where you were executing in the loop and just continue.

Best Regards,
Brandon Fisher

Hi Brandon, 

Thank you for your response. Please see the feedback from our customer.

"Based on the information you've shared, here's the basic flow I'm going to try:

MAIN():
Set up ADC12 to write to ADC12MEM0
Set up TB0 for 256 Hz interrupt
Start TB0
__enable_interrupts()
__no_operation()

while (1) {
while (sample_count == current_sample_count)
Wait for ADC to generate another value
Perform necessary work on the value in array[current_sample_count]
current_sample_count++
If current_sample_count > max, currnet_sample_count = 0
}

TB0 ISR:
Start ADC12
__bic_SR_register_on_exit(LPM3_bits)
__no_operation()

ADC12MEM0 ISR:
Read MEM0 into array[sample_count)
sample_count++
If sample_count > max, sample_count = 0
__bic_SR_register_on_exit(LPM3_bits)
__no_operation()


This means MSP doesn't ever go into LPM0 but I'm not worried about that in my application. I could perhaps go into LPM0 during the "Wait for ADC to generate another value" loop."

Thank you for extending your help. Your support is much appreciated.

Kind regards, 

Marvin

Hi Brandon, 

Please see the feedback from our customer. 

"I checked out the response in E2E. I had gone ahead with my plan and that seems to be working quite well. It was good to get some validation from Brandon, though.

Thanks so much for your help, and please thank Brandon for me!"

Your support is much appreciated. Thank you for your help.

Kind regards, 

Marvin