trigger interrupt

why don't the docs make it apparrent that this is possible, yet alone required?

main.c

@@ -16,14 +16,46 @@
 #include "Crystalfontz128x128_ST7735.h"
 #include <stdio.h>
 #include "buttons.h"
+#include "sampling.h"
+#include <math.h>
+#include "inc/hw_memmap.h"
+#include "driverlib/gpio.h"
+#include "driverlib/pwm.h"
+#include "driverlib/pin_map.h"
+#define PWM_FREQUENCY 20000 // PWM frequency = 20 kHz
 
 uint32_t gSystemClock; // [Hz] system clock frequency
 volatile uint32_t gTime = 0; // time in hundredths of a second
 
-int main(void)
-{
+// start a pwm test signal
+void start_signal() {
+  // configure M0PWM2, at GPIO PF2, BoosterPack 1 header C1 pin 2
+  SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOF);
+  GPIOPinTypePWM(GPIO_PORTF_BASE, GPIO_PIN_2);
+  GPIOPinConfigure(GPIO_PF2_M0PWM2);
+  GPIOPadConfigSet(GPIO_PORTF_BASE, GPIO_PIN_2, GPIO_STRENGTH_2MA,
+                   GPIO_PIN_TYPE_STD);
+  // configure the PWM0 peripheral, gen 1, outputs 2 and 3
+  SysCtlPeripheralEnable(SYSCTL_PERIPH_PWM0);
+  // use system clock without division
+  PWMClockSet(PWM0_BASE, PWM_SYSCLK_DIV_1);
+  PWMGenConfigure(PWM0_BASE, PWM_GEN_1,
+                  PWM_GEN_MODE_DOWN | PWM_GEN_MODE_NO_SYNC);
+  PWMGenPeriodSet(PWM0_BASE, PWM_GEN_1,
+                  roundf((float)gSystemClock / PWM_FREQUENCY));
+  PWMPulseWidthSet(PWM0_BASE, PWM_OUT_2,
+                   roundf((float)gSystemClock / PWM_FREQUENCY * 0.4f));
+  PWMOutputState(PWM0_BASE, PWM_OUT_2_BIT, true);
+  PWMGenEnable(PWM0_BASE, PWM_GEN_1);
+}
+
+int main(void) {
     IntMasterDisable();
 
+    start_signal();
+
+    start_sampler();
+
     // Enable the Floating Point Unit, and permit ISRs to use it
     FPUEnable();
     FPULazyStackingEnable();

sampling.c

@@ -0,0 +1,68 @@
+#include <stdint.h>
+#include <stdbool.h>
+#include "inc/tm4c1294ncpdt.h"
+#include "driverlib/adc.h"
+#include "driverlib/pin_map.h"
+#include "driverlib/gpio.h"
+#include "driverlib/sysctl.h"
+#include "driverlib/interrupt.h"
+#include "sysctl_pll.h"
+#include "inc/hw_types.h"
+#include "inc/hw_memmap.h"
+#include <math.h>
+#include "buttons.h"
+#include "sampling.h"
+
+// index wrapping macro
+#define ADC_BUFFER_WRAP(i) ((i) & (ADC_BUFFER_SIZE - 1))
+// latest sample index
+volatile int32_t gADCBufferIndex = ADC_BUFFER_SIZE - 1;
+volatile uint16_t gADCBuffer[ADC_BUFFER_SIZE]; // circular buffer
+volatile uint32_t gADCErrors = 0; // number of missed ADC deadlines
+void ADC_ISR(void)
+{
+    // clear ADC1 sequence0 interrupt flag in the ADCISC register
+    //HWREGBITW(ADC1_ISC_R, 1) = 1;
+    ADC1_ISC_R |= 1;
+
+    // check for ADC FIFO overflow
+    if(ADC1_OSTAT_R & ADC_OSTAT_OV0) {
+    gADCErrors++; // count errors
+    ADC1_OSTAT_R = ADC_OSTAT_OV0; // clear overflow condition
+    }
+    gADCBufferIndex = ADC_BUFFER_WRAP(gADCBufferIndex + 1);
+    // read sample from the ADC1 sequence 0 FIFO
+    gADCBuffer[gADCBufferIndex] = (ADC1_SSFIFO0_R & ADC_SSFIFO0_DATA_M);
+}
+
+
+void start_sampler() {
+    SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOE);
+    GPIOPinTypeADC(GPIO_PORTE_BASE,
+                    GPIO_PIN_0); // GPIO setup for analog input AIN3
+    // initialize ADC peripherals
+    SysCtlPeripheralEnable(SYSCTL_PERIPH_ADC0);
+    SysCtlPeripheralEnable(SYSCTL_PERIPH_ADC1);
+    // ADC clock
+    uint32_t pll_frequency = SysCtlFrequencyGet(CRYSTAL_FREQUENCY);
+    uint32_t pll_divisor =
+        (pll_frequency - 1) / (16 * ADC_SAMPLING_RATE) + 1; // round up
+    ADCClockConfigSet(ADC0_BASE, ADC_CLOCK_SRC_PLL | ADC_CLOCK_RATE_FULL,
+                    pll_divisor);
+    ADCClockConfigSet(ADC1_BASE, ADC_CLOCK_SRC_PLL | ADC_CLOCK_RATE_FULL,
+                    pll_divisor);
+    // choose ADC1 sequence 0; disable before configuring
+    ADCSequenceDisable(ADC1_BASE, 0);
+    ADCSequenceConfigure(ADC1_BASE, 0, ADC_TRIGGER_ALWAYS,
+                        0); // specify the "Always" trigger
+    // in the 0th step, sample channel 3 (AIN3)
+    // enable interrupt, and make it the end of sequence
+    ADCSequenceStepConfigure(ADC1_BASE, 0, 0, ADC_CTL_CH3 | ADC_CTL_END | ADC_CTL_IE);
+    // enable the sequence. it is now sampling
+    ADCSequenceEnable(ADC1_BASE, 0);
+    // enable sequence 0 interrupt in the ADC1 peripheral
+    ADCIntEnable(ADC1_BASE, 0); // INT_ADC1SS0
+    IntPrioritySet(INT_ADC1SS0, 0); // set ADC1 sequence 0 interrupt priority
+    // enable ADC1 sequence 0 interrupt in int. controller
+    IntEnable(INT_ADC1SS0);
+}

sampling.h

@@ -0,0 +1,11 @@
+#ifndef SAMPLING_H_
+#define SAMPLING_H_
+
+#include <stdint.h>
+
+#define ADC_BUFFER_SIZE 2048 // size must be a power of 2
+
+// initialize ADC and ISR
+void start_sampler(void);
+
+#endif /* SAMPLING_H_ */

tm4c1294ncpdt_startup_ccs.c

@@ -34,6 +34,7 @@ static void NmiSR(void);
 static void FaultISR(void);
 static void IntDefaultHandler(void);
 void ButtonISR(void);
+void ADC_ISR(void);
 
 //*****************************************************************************
 //
@@ -131,7 +132,7 @@ void (* const g_pfnVectors[])(void) =
     IntDefaultHandler,                      // PWM Generator 3
     IntDefaultHandler,                      // uDMA Software Transfer
     IntDefaultHandler,                      // uDMA Error
-    IntDefaultHandler,                      // ADC1 Sequence 0
+    ADC_ISR,                                // ADC1 Sequence 0
     IntDefaultHandler,                      // ADC1 Sequence 1
     IntDefaultHandler,                      // ADC1 Sequence 2
     IntDefaultHandler,                      // ADC1 Sequence 3