TM4C1231H6PM: ADC Digital Comparator output

Suraj Pramanik

Part Number: TM4C1231H6PM

Trigger ADC Digital Comparator by timer in every 1ms

#define ADC_SEQUENCE_NUMBER 3

void adc_comparator_config(void) {
    SysCtlPeripheralEnable(SYSCTL_PERIPH_ADC0);
    SysCtlPeripheralReset(SYSCTL_PERIPH_ADC0);

    GPIOPinTypeADC(GPIO_PORTD_BASE, GPIO_PIN_0);
    GPIOPinTypeGPIOOutput(GPIO_PORTD_BASE, GPIO_PIN_2);
    GPIOPinWrite(GPIO_PORTD_BASE, GPIO_PIN_2, GPIO_PIN_2);

    //
    // Disable the sequence.
    //
    ADCSequenceDisable(ADC0_BASE, ADC_SEQUENCE_NUMBER);
    ADCSequenceDisable(ADC0_BASE, 0);
    ADCIntClear(ADC0_BASE, ADC_SEQUENCE_NUMBER); // Clear any interrupts

    //
    // Reconfigure and enable the sequence.
    //
    ADCSequenceConfigure(ADC0_BASE, ADC_SEQUENCE_NUMBER,
                         ADC_TRIGGER_TIMER, 3);
    ADCSequenceStepConfigure(ADC0_BASE, ADC_SEQUENCE_NUMBER, 0,
                             ADC_CTL_CH7 | ADC_CTL_END | ADC_CTL_IE | ADC_CTL_CMP7);
	ADCSequenceEnable(ADC0_BASE, ADC_SEQUENCE_NUMBER);

    // Reset the ADC comparator
    ADCComparatorReset(ADC0_BASE, ADC_CTL_CH7, true, true);
    ADCComparatorIntClear(ADC0_BASE, ADC_SEQUENCE_NUMBER);
    
    // Configure the ADC comparator
    ADCComparatorConfigure(ADC0_BASE, ADC_CTL_CMP7,
                           ADC_COMP_INT_HIGH_ALWAYS);
    ADCComparatorRegionSet(ADC0_BASE, ADC_CTL_CH7, 1024, 3600); // High threshold = 3600mV
    ADCComparatorIntEnable(ADC0_BASE, ADC_SEQUENCE_NUMBER);
    
    // Register the interrupt handler
    IntMasterEnable();
    ADCIntRegister(ADC0_BASE, ADC_SEQUENCE_NUMBER, adc_comparator_int_handler);
    ADCIntEnable(ADC0_BASE, ADC_SEQUENCE_NUMBER);
    IntEnable(INT_ADC0SS3);

}

// Once interrupt trigger, get the ADC value and print.
void adc_comparator_int_handler(void) {
    ADCComparatorIntClear(ADC0_BASE, ADC_SEQUENCE_NUMBER);
    uint32_t pui32ADC0Value[8] = {0};
    ADCSequenceDataGet(ADC0_BASE, ADC_SEQUENCE_NUMBER, pui32ADC0Value);
    printf("ADC value: %d", pui32ADC0Value[0]);
}

// Enable hw timer to trigger the ADC in every 1ms
void hw_timer_init()
{
    SysCtlPeripheralEnable(SYSCTL_PERIPH_WTIMER1);

    TimerDisable(WTIMER1_BASE, TIMER_A);

    TimerConfigure(WTIMER1_BASE, TIMER_CFG_A_PERIODIC);
    TimerLoadSet(WTIMER1_BASE, TIMER_A, SysCtlClockGet() / 1000 * 1);
    TimerControlTrigger(WTIMER1_BASE, TIMER_A, true);
    TimerEnable(WTIMER1_BASE,TIMER_A);

}

Problem statement: ADC digital Comparator interrupt status is not set (ADCComparatorIntStatus(ADC0_BASE)).

Q1. How to get/calculate ADC Digital Comparator value(read value from which register)? (I would like to make sure that the ADC value is higher than 3600 mV)

Q2. Is the ADC Digital Comparator configuration correct?
Q3. How to make sure that the interrupt trigger due to the ADC value is higher than threshold?

Please help to clarify the problems. Thanks for your time and help.

Regards,

Suraj Pramanik

over 2 years ago

0 Charles Tsai over 2 years ago

TI__Guru**** 190616 points

Hi Suraj,

In your code I don't see you enable PortD if you want to use PD0 for AIN7. You should have the below line of code.

SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOD);

0 Charles Tsai over 2 years ago in reply to Charles Tsai

TI__Guru**** 190616 points

Additional comments for your code.

You wrote the below code. ADC_CTL_CMP7 does not need to go with ADC_CTL_CH7. There is no strict one to one mapping here. You could have use ADC_CTL_CMP0 as the comparator for ADC_CTL_CH7 or another channel. With that said, using ADC_CTL_CMP7 is ok here. Just wanted to clarify there is no hard association between ADC_CTL_CMP7 and ADC_CTL_CH7.

ADCSequenceStepConfigure(ADC0_BASE, ADC_SEQUENCE_NUMBER, 0,
ADC_CTL_CH7 | ADC_CTL_END | ADC_CTL_IE | ADC_CTL_CMP7);

You wrote the below code. You are supposed to provide the bit-mapped interrupts status to clear, not ADC_SEQUENCE_NUMBER which is 3 all the time. Please refer to peripheral driverlib user's guide.

ADCComparatorIntClear(ADC0_BASE, ADC_SEQUENCE_NUMBER);

You wrote below line. You need to be aware that it is the conversion values that the the comparator is comparing against, not the voltage. When you input 3600, this does NOT mean 3600mV but rather a ADC conversion value. Since ADC is 12 bit and suppose the VDDA is 3.3V, 3600 would mean 3.3 * (3600 / 4096) = 2.9V. Is that what you really want? It is your application. You will need to figure what is the upper limit you want to trigger an interrupt.

ADCComparatorRegionSet(ADC0_BASE, ADC_CTL_CH7, 1024, 3600); // High threshold = 3600mV

0 Suraj Pramanik over 2 years ago in reply to Charles Tsai

Prodigy 10 points

Hello Charles,
Thanks for pointing it out about the ADCComparatorIntClear function usage. Now I am pretty clear how to calculate the higher threshold value.

I have a further question about the interrupt configurations. When I dump the

HWREG(ADC0_BASE + ADC_O_IM) register, I see the value is 0x80008(bit 3 and bit 19 are set).

Is it okay to set two different interrupt setting?
I can get interrupt from the ADC Int setting, however cannot see any interrupt from the digital comparator.

0 Charles Tsai over 2 years ago in reply to Suraj Pramanik

TI__Guru**** 190616 points

Suraj Pramanik said:
HWREG(ADC0_BASE + ADC_O_IM) register, I see the value is 0x80008(bit 3 and bit 19 are set).

Is it okay to set two different interrupt setting?
I can get interrupt from the ADC Int setting, however cannot see any interrupt from the digital comparator.

Hi,

Can you remove ADC_CTL_IE? Does that make a difference?

0 Suraj Pramanik over 2 years ago in reply to Charles Tsai

Prodigy 10 points

No. If I remove this, the interrupt callback function (adc_comparator_int_handler) never execute.

0 Charles Tsai over 2 years ago in reply to Suraj Pramanik

TI__Guru**** 190616 points

Hi,

Suraj Pramanik said:
Is it okay to set two different interrupt setting?
I can get interrupt from the ADC Int setting, however cannot see any interrupt from the digital comparator.

Suraj Pramanik said:
HWREG(ADC0_BASE + ADC_O_IM) register, I see the value is 0x80008(bit 3 and bit 19 are set).

I think in your case it should be ok to enable both both DCONSS3 and MASK3 bits in ADCIM register. The reason is that you are routing the input value to the digital comparator. The input value will not be saved in the FIFO. In your ISR, you should not expect to read the ADC value but instead check if DCONSS3 is set. If it is set, it means the upper threshold is detected.