Doubts in code, while reading ADC-input in the simplest of case

Other Parts Discussed in Thread: TM4C1230D5PM

Hi All.

We have written the simplest of code (hopefully), trying to read a ADC value on a TM4C1230D5PM.

However, the code does not work (always shows values from 1405-1409, irrespective of whether the analog-voltage source is on/off, or the value of analog-voltage when the analog-voltage source is on).

#include <stdbool.h>
#include <stdint.h>
#include "inc/hw_memmap.h"
#include "driverlib/adc.h"
#include "driverlib/gpio.h"
#include "driverlib/pin_map.h"
#include "driverlib/sysctl.h"
#include "driverlib/uart.h"
#include "utils/uartstdio.h"

uint32_t pui32ADC0Value[1];

void adc_initialize(void)
{

    /*
     * Set the clocking to run directly from the crystal.
     */
    ROM_SysCtlClockSet(SYSCTL_SYSDIV_1 | SYSCTL_USE_OSC | SYSCTL_OSC_MAIN |
                       SYSCTL_XTAL_16MHZ);

    //
    // The ADC0 peripheral must be enabled for use.
    //
    SysCtlPeripheralEnable(SYSCTL_PERIPH_ADC0);


    //
    // For this example ADC0 is used with AIN0 on port E7.
    // The actual port and pins used may be different on your part, consult
    // the data sheet for more information.  GPIO port E needs to be enabled
    // so these pins can be used.
    // TODO: change this to whichever GPIO port you are using.
    //
    SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOE);


    //
    // Select the analog ADC function for these pins.
    // Consult the data sheet to see which functions are allocated per pin.
    // TODO: change this to select the port/pin you are using.
    //
    GPIOPinTypeADC(GPIO_PORTE_BASE, GPIO_PIN_1);


    //
    // Enable sample sequence 3 with a processor signal trigger.  Sequence 3
    // will do a single sample when the processor sends a signal to start the
    // conversion.  Each ADC module has 4 programmable sequences, sequence 0
    // to sequence 3.  This example is arbitrarily using sequence 3.
    //
    ADCSequenceConfigure(ADC0_BASE, 3, ADC_TRIGGER_PROCESSOR, 0);


    //
    // Configure step 0 on sequence 3.  Sample channel 0 (ADC_CTL_CH0) in
    // single-ended mode (default) and configure the interrupt flag
    // (ADC_CTL_IE) to be set when the sample is done.  Tell the ADC logic
    // that this is the last conversion on sequence 3 (ADC_CTL_END).  Sequence
    // 3 has only one programmable step.  Sequence 1 and 2 have 4 steps, and
    // sequence 0 has 8 programmable steps.  Since we are only doing a single
    // conversion using sequence 3 we will only configure step 0.  For more
    // information on the ADC sequences and steps, reference the datasheet.
    //
    ADCSequenceStepConfigure(ADC0_BASE, 3, 0, ADC_CTL_CH0 | ADC_CTL_IE |
                             ADC_CTL_END);


    //
    // Since sample sequence 3 is now configured, it must be enabled.
    //
    ADCSequenceEnable(ADC0_BASE, 3);


    //
    // Clear the interrupt status flag.  This is done to make sure the
    // interrupt flag is cleared before we sample.
    //
    ADCIntClear(ADC0_BASE, 3);

}

void process()
{
    //
    // Sample AIN0.
    //
    if(1)
    {
        //
        // Trigger the ADC conversion.
        //
        ADCProcessorTrigger(ADC0_BASE, 3);

        //
        // Wait for conversion to be completed.
        //
        while(!ADCIntStatus(ADC0_BASE, 3, false))
        {
        }

        //
        // Clear the ADC interrupt flag.
        //
        ADCIntClear(ADC0_BASE, 3);

        //
        // Read ADC Value.
        //
        ADCSequenceDataGet(ADC0_BASE, 3, pui32ADC0Value);

        //
        // Display the AIN0 (PE7) digital value on the console.
        //
        info_log("AIN0 = %u", pui32ADC0Value[0]);
    }
}


int main(int argc, char** argv)
{

    /*
     * All application-specific logger/timer initialization
     */

    adc_initialize();
    info_log("INIT done");

    while(1)
    {
        startAndCountdownTimer(1, 0);
        process();
    }

    return 0;
}

The above code has been picked up from the example single-ended ADC example from the gcc-toolchain.

Kindly provide pointers on what is missing.

We will be grateful.

Thanks and Regards,

Ajay