ADC采样得到的值为什么都是0？

我下边的代码的目的是从UART得到信号后，ADC采集20个信号，然后将信号返回到UART，其中ADC信号采集部分是参照官方例子(见附件)写的

官方的例子可以运行并得到变化的采样值，但是我的程序得到的值都是0，是哪里没有配置合适吗

#include <stdbool.h>
#include <stdint.h>
#include "inc/hw_ints.h"
#include "inc/hw_memmap.h"
#include "inc/hw_types.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"
#include "driverlib/timer.h"

uint8_t State = 0;
uint32_t adc_count = 0;
uint32_t adc_val[20];
uint32_t total_samples = 20;
uint32_t adc_v;

//! - ADC0 peripheral
//! - GPIO Port E peripheral (for ADC0 pins)
//! - AIN0 - PE3
//! - AIN1 - PE2

//! - UART0 peripheral
//! - GPIO Port A peripheral (for UART0 pins)
//! - UART0RX - PA0
//! - UART0TX - PA1
//! - UART1RX - PB0
//! - UART1TX - PB1

void UART0_IntHandler(void)
{
    uint32_t ui32Status;
    ui32Status = UARTIntStatus(UART0_BASE, true); //get interrupt status
    UARTIntClear(UART0_BASE, ui32Status); //clear the asserted interrupts

	while(UARTCharsAvail(UART0_BASE))
	{
		uint32_t get_char;
		get_char = UARTCharGetNonBlocking(UART0_BASE);
		switch(get_char)
		{
		case 0x00000001:
			State = 1;
			break;
		case 0x00000002:
			State = 2;
			break;
		case 0x00000003:
			State = 3;
			break;
		case 0x00000004:
			State = 4;
			break;
		default:
			break;
		}
	}
}
void UART1_IntHandler(void)
{
	uint32_t ui32Status;
	ui32Status = UARTIntStatus(UART1_BASE, true); //get interrupt status
	UARTIntClear(UART1_BASE, ui32Status); //clear the asserted interrupts

	while(UARTCharsAvail(UART1_BASE))
	{
		uint32_t get_char;
		get_char = UARTCharGetNonBlocking(UART1_BASE);
		switch(get_char)
		{
		case 0x00000001:
			break;
		case 0x00000002:
			break;
		case 0x00000003:
			break;
		default:
			break;
		}
	}
}
void ADC_IntHandler(void)
{
	ADCIntClear(ADC0_BASE,3);
	ADCSequenceDataGet(ADC0_BASE, 3,adc_v);
	adc_val[adc_count++] = adc_v;
}
void UART0_init(void)
{
	SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOA);
	GPIOPinConfigure(GPIO_PA0_U0RX);
	GPIOPinConfigure(GPIO_PA1_U0TX);
	SysCtlPeripheralEnable(SYSCTL_PERIPH_UART0);
	UARTClockSourceSet(UART0_BASE, UART_CLOCK_PIOSC);
	GPIOPinTypeUART(GPIO_PORTA_BASE, GPIO_PIN_0 | GPIO_PIN_1);
	UARTStdioConfig(0, 115200, 16000000);

	IntEnable(INT_UART0); //enable the UART interrupt
	UARTIntEnable(UART0_BASE, UART_INT_RX | UART_INT_RT); //only enable RX and TX interrupts
}
void UART1_init(void)
{
	SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOB);
	GPIOPinConfigure(GPIO_PB0_U1RX);
	GPIOPinConfigure(GPIO_PB1_U1TX);
	SysCtlPeripheralEnable(SYSCTL_PERIPH_UART1);
	UARTClockSourceSet(UART1_BASE, UART_CLOCK_PIOSC);
	GPIOPinTypeUART(GPIO_PORTB_BASE, GPIO_PIN_0 | GPIO_PIN_1);
	UARTStdioConfig(1, 115200, 16000000);

	IntEnable(INT_UART0); //enable the UART interrupt
	UARTIntEnable(UART0_BASE, UART_INT_RX | UART_INT_RT); //only enable RX and TX interrupts
}
void ADC_init(void)
{
	SysCtlPeripheralEnable(SYSCTL_PERIPH_ADC0);
	SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOE);
	GPIOPinTypeADC(GPIO_PORTE_BASE,GPIO_PIN_3 | GPIO_PIN_2);
	ADCSequenceConfigure(ADC0_BASE, 3,ADC_TRIGGER_TIMER, 0);
    ADCSequenceStepConfigure(ADC0_BASE, 3, 0, ADC_CTL_D | ADC_CTL_CH0 |
                             ADC_CTL_IE | ADC_CTL_END);
	//ADCReferenceSet(ADC0_BASE,ADC_REF_INT);
	ADCIntEnable(ADC0_BASE,3);
	IntEnable(INT_ADC0SS3);
	ADCIntClear(ADC0_BASE, 3);
	ADCIntRegister(ADC0_BASE,3,ADC_IntHandler);  // 注册序列3中断 函数
	ADCSequenceEnable(ADC0_BASE, 3);

}
void TIMER0_init(void)
{
	SysCtlPeripheralEnable(SYSCTL_PERIPH_TIMER0);//使能TIMER0
	TimerConfigure(TIMER0_BASE, TIMER_CFG_PERIODIC);//周期性计数模式
	//TimerLoadSet(TIMER0_BASE, TIMER_A,SysCtlClockGet() / 12800);
	TimerLoadSet(TIMER0_BASE, TIMER_A,SysCtlClockGet() / 100);
	TimerADCEventSet(TIMER0_BASE,TIMER_ADC_TIMEOUT_A);//超时触发采样设置
	TimerEnable(TIMER0_BASE, TIMER_A);//TIMER0A开始计数，当计数值等于TimerLoadSet，触发中断
}
void store_raw_data(void)
{
	adc_count = 0;
	TimerControlTrigger(TIMER0_BASE,TIMER_A,true);

	while(adc_count < total_samples){};

	TimerControlTrigger(TIMER0_BASE,TIMER_A,false);
}
int main(void)
{

    uint32_t pui32ADC0Value[1];

    SysCtlClockSet(SYSCTL_SYSDIV_10 | SYSCTL_USE_PLL | SYSCTL_OSC_MAIN |
                   SYSCTL_XTAL_16MHZ);
    //这个函数定义结果，外部输入16MHz，经PLL至400MHz，再2分频（芯片自带）至200MHz，再10分频至20MHz。因此这个设置的结果为主频20MHz。

    IntMasterEnable();

    UART0_init();
    ADC_init();
    TIMER0_init();

    UARTprintf("ADC ->\n");
    UARTprintf("  Type: differential\n");
    UARTprintf("  Samples: One\n");
    UARTprintf("  Update Rate: 250ms\n");
    UARTprintf("  Input Pin: (AIN0/PE3 - AIN1/PE2)\n\n");


	while(1){
		switch(State)
		{
		case 1:
			UARTprintf("00000001");
			State = 0;
			break;
		case 2:
			UARTprintf("00000002");
			State = 0;
			break;
		case 3:
			UARTprintf("00000003");
			State = 0;
			break;
		case 4:
			store_raw_data();
			uint8_t i;
			for(i=0;i<total_samples;i++) UARTprintf("%4d\r",adc_val[i]);
			State = 0;
			break;
		default:
			break;
		}

	}
}