CCS/EK-TM4C1294XL: ADC not running at 2MSPS (capped at 1MSPS)

Sorry, there is an issue with the documentation. The ADC converter clock is really PLL VCO divided by 2, then divided by the value in the CLKDIV field (CLKDIV+1)  of the ADCCC register. You cannot get 32MHz ADC clock running the PLL VCO at 480MHz, but running the PLL VCO at 320MHz, you can get 2MSPS by using divide by 5.

The issue is further complicated by the fact that at 2MSPS there is not enough time to use TivaWare calls in the interrupt service routine to toggle a GPIO pin and clear the interrupt. (Much less, read and store the sample.) In the example below I replaced some TivaWare calls with direct register writes to avoid the overhead of the subroutine calls.

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#include <stdint.h>
#include <stdbool.h>
#include "inc/hw_types.h"
#include "inc/hw_ints.h"
#include "inc/hw_adc.h"
#include "inc/hw_memmap.h"
#include "driverlib/sysctl.h"
#include "driverlib/gpio.h"
#include "driverlib/adc.h"
#include "driverlib/timer.h"
#include "driverlib/interrupt.h"


#define USER_LED1  GPIO_PIN_0
#define USER_LED2  GPIO_PIN_1
void init_TIMER(void);
void init_ADC(void);

uint32_t ui32SysClock;

int
main(void)
{

    //
    // Run from the PLL at 120 MHz.
    //
    ui32SysClock = SysCtlClockFreqSet((SYSCTL_XTAL_25MHZ |
                                       SYSCTL_OSC_MAIN |
                                       SYSCTL_USE_PLL |
                                       SYSCTL_CFG_VCO_320), 120000000);

    SysCtlPeripheralEnable(SYSCTL_PERIPH_TIMER0);  //Enable the clock to TIMER0
    SysCtlPeripheralEnable(SYSCTL_PERIPH_ADC0);    //Enable the clock to ADC module
    //
    // Enable and wait for the port to be ready for access
    //
    SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOE);
    SysCtlPeripheralEnable(SYSCTL_PERIPH_GPION);
    while(!SysCtlPeripheralReady(SYSCTL_PERIPH_GPION))
    {
    }
    
    //
    // Configure the GPIO port for the LED operation.
    //
    GPIOPinTypeGPIOOutput(GPIO_PORTN_BASE, (USER_LED1|USER_LED2));

    init_ADC();
    init_TIMER();
    IntMasterEnable();
    TimerEnable(TIMER0_BASE, TIMER_A); // Start everything
    //
    // Loop Forever
    //
    while(1)
    {
//        GPIOPinWrite(GPIO_PORTN_BASE, (USER_LED1|USER_LED2), 0);
    	HWREG(GPIO_PORTN_BASE + 4) = 0;
    }
}

void init_TIMER()
{
    TimerConfigure(TIMER0_BASE, TIMER_CFG_SPLIT_PAIR | TIMER_CFG_A_PERIODIC);
    // Set sample frequency to 2MHz (every 62.5uS)
    TimerLoadSet(TIMER0_BASE, TIMER_A, 40 - 1);   //TODO: Timer Load Value is set here
    TimerControlTrigger(TIMER0_BASE, TIMER_A, true);
    TimerControlStall(TIMER0_BASE, TIMER_A, true); //Assist in debug by stalling timer at breakpoints
}

void init_ADC()
{
    GPIOPinTypeADC(GPIO_PORTE_BASE, GPIO_PIN_2);
    SysCtlDelay(80u);

    // Use ADC0 sequence 0 to sample channel 0 once for each timer period
    ADCClockConfigSet(ADC0_BASE, ADC_CLOCK_SRC_PLL | ADC_CLOCK_RATE_FULL, 5);

    SysCtlDelay(10); // Time for the clock configuration to set

    IntDisable(INT_ADC0SS0);
    ADCIntDisable(ADC0_BASE, 0u);
    ADCSequenceDisable(ADC0_BASE,0u);
    // With sequence disabled, it is now safe to load the new configuration parameters

    ADCSequenceConfigure(ADC0_BASE, 0u, ADC_TRIGGER_TIMER, 0u);
    ADCSequenceStepConfigure(ADC0_BASE,0u,0u,ADC_CTL_CH0 | ADC_CTL_END | ADC_CTL_IE);
    ADCSequenceEnable(ADC0_BASE,0u); //Once configuration is set, re-enable the sequencer
    ADCIntClear(ADC0_BASE,0u);
    ADCIntEnable(ADC0_BASE, 0u);
    IntEnable(INT_ADC0SS0);

}

void ADC0SS0IntHandler(void)
{
	HWREG(GPIO_PORTN_BASE + 4) = 1;
//	GPIOPinWrite(GPIO_PORTN_BASE, (USER_LED1|USER_LED2), USER_LED1);
    HWREG(ADC0_BASE + ADC_O_ISC) = 1 << 0;
//    ADCIntClear(ADC0_BASE, 0);
}