CCS/TM4C123GH6PM: ADC Not Functioning

Cole Mowrer said:

However, now the program is getting stuck in FaultISR().

    //
    // Enable peripheral ADC0 and reset to apply
    //
    SysCtlPeripheralEnable(SYSCTL_PERIPH_ADC0);
    SysCtlPeripheralReset(SYSCTL_PERIPH_ADC0);

    //
    // Disable ADC0 sequencer 0 and reconfigure ADC0 sequencer
    //
    ADCSequenceDisable(ADC0_BASE,0);

Where the first ADC0 register which is attempted to be accessed by the ADCSequenceDisable() function is the ADC Active Sample Sequencer register at which the bus fault occurred.

On the Tiva parts the datasheet mentions there may be latency from when a peripheral is enabled or taken out of reset before the peripheral is ready to be accessed. Attempting to access a peripheral before it is ready results in a bus fault. By changing the ConfigureADC function to wait for the ADC0 peripheral to be become ready stopped the program getting stuck in the fault ISR:

    //
    // Enable peripheral ADC0 and reset to apply
    //
    SysCtlPeripheralEnable(SYSCTL_PERIPH_ADC0);
    while (!SysCtlPeripheralReady (SYSCTL_PERIPH_ADC0))
    {
    }
    SysCtlPeripheralReset(SYSCTL_PERIPH_ADC0);
    while (!SysCtlPeripheralReady (SYSCTL_PERIPH_ADC0))
    {
    }

Note that the actual latency for a peripheral to become ready is not specified in the datasheet, and so it is difficult to know if a program will encounter the fault. For robustness a while (!SysCtlPeripheralReady()) loop should be be used before the first attempt to access a peripheral.

Having stopped the program getting stuck in the faultISR found that was then getting stuck waiting for the ADC conversion to finish. Realized that the program was missing a call to ADCSequenceEnable() to enabled the ADC sequencer. Following adding the ADCSequenceEnable(ADC0_BASE, 0) call to ConfigureADC() the program is now running successfully. The complete code is:

#include <stdio.h>
#include <stdbool.h>
#include <stdint.h>
#include "driverlib/adc.h"
#include "driverlib/debug.h"
#include "driverlib/fpu.h"
#include "driverlib/gpio.h"
#include "driverlib/interrupt.h"
#include "driverlib/pin_map.h"
#include "driverlib/rom.h"
#include "driverlib/sysctl.h"
#include "driverlib/uart.h"
#include "inc/hw_adc.h"
#include "inc/hw_gpio.h"
#include "inc/hw_ints.h"
#include "inc/hw_memmap.h"
#include "inc/hw_sysctl.h"
#include "utils/uartstdio.h"
#include "driverlib/rom.h"

//*****************************************************************************
//
// Configure the ADC and its pins.
//
//*****************************************************************************
void
ConfigureADC(void)
{
    //-----------ADC Setup----------------
    //------------------------------------
    //
    // Enable peripheral ADC0 and reset to apply
    //
    SysCtlPeripheralEnable(SYSCTL_PERIPH_ADC0);
    while (!SysCtlPeripheralReady (SYSCTL_PERIPH_ADC0))
    {
    }
    SysCtlPeripheralReset(SYSCTL_PERIPH_ADC0);
    while (!SysCtlPeripheralReady (SYSCTL_PERIPH_ADC0))
    {
    }

    //
    // Disable ADC0 sequencer 0 and reconfigure ADC0 sequencer
    //
    ADCSequenceDisable(ADC0_BASE,0);
    ADCSequenceConfigure(ADC0_BASE, 0, ADC_TRIGGER_PROCESSOR, 0);
    ADCSequenceStepConfigure(ADC0_BASE, 0, 0, ADC_CTL_TS /*AIN0*/ | ADC_CTL_IE | ADC_CTL_END);

    //
    // Enable the sequence but do not start it yet.
    //
    ADCSequenceEnable(ADC0_BASE, 0);

    //
    // Enable GPIO Port E and set Pin 3 to ADC Type
    //
    SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOE);
    GPIOPinTypeADC(GPIO_PORTE_BASE, GPIO_PIN_3);
}

//*****************************************************************************
//
// Configure the UART and its pins.  This must be called before UARTprintf().
//
//*****************************************************************************
void
ConfigureUART(void)
{
    //-----------UART Setup---------------
    //------------------------------------
    //
    // Enable GPIO and UART 1 Peripherals
    //
    SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOB);
    SysCtlDelay(3);
    SysCtlPeripheralEnable(SYSCTL_PERIPH_UART1);
    SysCtlDelay(3);

    //
    // Configure GPIO Pins for UART Mode
    //
    GPIOPinConfigure(GPIO_PB1_U1TX);
    GPIOPinTypeUART(GPIO_PORTB_BASE, GPIO_PIN_1);

    //
    // Use the internal 16MHz oscillator as the UART clock source.
    //
    UARTClockSourceSet(UART1_BASE, UART_CLOCK_PIOSC);

    //
    // Initialize UART (port, baud rate, clock source)
    //
    UARTStdioConfig(0, 9600, 16000000);
}


int main(void) {
    uint32_t result;
    volatile float voltage;
    //
    // Clock Setup to 40 MHz
    //
    SysCtlClockSet(SYSCTL_SYSDIV_5|SYSCTL_USE_PLL|SYSCTL_OSC_MAIN|SYSCTL_XTAL_16MHZ);

    SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOF);
    GPIOPinTypeGPIOOutput(GPIO_PORTF_BASE, GPIO_PIN_2);

    ConfigureADC();
    ConfigureUART();

    UARTprintf("Hello, world!\n");

    while(1)
    {
            //
            // Turn on the BLUE LED.
            //
            GPIOPinWrite(GPIO_PORTF_BASE, GPIO_PIN_2, GPIO_PIN_2);

            //
            // Delay for a bit.
            //
            SysCtlDelay(SysCtlClockGet() / 10 / 3);

                //---------------ADC-----------------
                //
                // request ADC conversion
                //
                ADCProcessorTrigger(ADC0_BASE, 0);

                //
                // Wait until the conversion is finished
                //
                while(!ADCIntStatus(ADC0_BASE, 0, false))
                {
                }

                //
                // Clear interrupt flag for ADC0 sequencer 3
                //
                ADCIntClear(ADC0_BASE, 0);

                //----------Process the Data---------------
                //
                // Read in the data and convert
                //
                ADCSequenceDataGet(ADC0_BASE, 0, &result);
                voltage = result*0.000805664;

            //
            // Turn off the BLUE LED.
            //
            GPIOPinWrite(GPIO_PORTF_BASE, GPIO_PIN_2, 0);

            //
            // Delay for a bit.
            //
            SysCtlDelay(SysCtlClockGet() / 10 / 3);
        }
}