Triggering ADC conversions with a timer on the MSP430FR5969

Question

I am trying to repeatedly sample one channel from the ADC on my MSP430FR5969 using timer TA0. Unfortunately, the timer doesn't appear to be causing conversions. I expect my issue lies in my configuration of the ADC control registers.

void init()
{
    // Set up clock
    CSCTL0_H = CSKEY >> 8;    // Unlock CS registers
    CSCTL2 |= SELA__LFMODCLK; // Set ACLK= MODCLK / 128
    CSCTL3 |= DIVA__1;        // Set divider for ACLK = 1
    CSCTL0_H = 0;             // Lock CS registers

    // Set up timer
    TA0CCR0 = 4;         // Period (should come to ~7.5kHz)
    TA0CCTL1 = OUTMOD_3; // CCR1 reset/set

    // Set up ref voltage
    REFCTL0 = REFVSEL_2 | REFTCOFF | REFON; // Set reference voltage to 2.5V

    // Set up ADC
    ADC12CTL0 = ADC12SHT0_0 | ADC12ON;      // Sampling time, ADC12 on
    ADC12CTL1 = ADC12SHS_1;                 // Use TA0.1 as sample and hold source
    ADC12CTL2 = ADC12RES__12BIT;            // 12-bit conversion results
    ADC12MCTL0 |= AUDIO_PIN | ADC12VRSEL_1; // A15 ADC input select; Vref=2.5V
    ADC12IER0 |= ADC12IE0;                  // Enable ADC conv complete interrupt
    ADC12IFGR0 &= ~ADC12IFG0;               // Clear interrupt flag
}

void start_samples()
{
    // Enable conversions
    ADC12CTL0 |= ADC12ENC;

    // Enable timer
    TA0CTL = TASSEL__ACLK | MC__UP | TACLR;

    // Enter LPM3, enable interrupts
    __bis_SR_register(LPM3_bits | GIE);
    __no_operation();
}

#pragma vector = ADC12_VECTOR
__interrupt void ADC12_ISR(void)
{
    // Push sample to buffer
    *dst++ = ADC12MEM0;
}

Answer 1

I use the MSP430FR5994, but I believe that the ADC12 is the same.

For repeated samples triggered on a timer, I believe that you need to set 2 more bits.

ADC12CTL1 = ADC12SHP | ADC12SHS_1 | ADC12CONSEQ_2;

You may also need to send one "start" command to start the process.

ADC12CTL0 |= ADC12ENC | ADC12SC;