TM4C123GH6PM: Problem with Timer interrupt handler

I am using IAR workbench. EK-TM4C123GXL launchpad

I wrote code to get square wave 2 msec period, 50% duty cycle.

Below code works fine. My problem is with interrupt handler. How to add interrupt handler function. For my code I have added cstartup_M.c file. Is it correct way to add. If no, please share correct way.

.............................code..................................

#include <stdbool.h>
#include <stdint.h>
#include "inc/tm4c123gh6pm.h"
#include "inc/hw_ints.h"
#include "inc/hw_memmap.h"
#include "driverlib/gpio.h"
#include "driverlib/interrupt.h"
#include "driverlib/pin_map.h"
#include "driverlib/sysctl.h"
#include "driverlib/timer.h"

volatile uint8_t state=0;

uint32_t freq=0;

void TIMER0A_Handler(void)
{
TimerIntClear(TIMER0_BASE, TIMER_TIMA_TIMEOUT);
state^=GPIO_PIN_1;
GPIOPinWrite(GPIO_PORTF_BASE,GPIO_PIN_1, state);
}

int main(void)
{

SysCtlClockSet(SYSCTL_SYSDIV_5 | SYSCTL_USE_PLL | SYSCTL_OSC_MAIN | SYSCTL_XTAL_16MHZ);
SysCtlDelay(3);
freq = SysCtlClockGet();   // 40Mhz
//GPIO Configuration
SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOF);
SysCtlDelay(3);
GPIOPinTypeGPIOOutput(GPIO_PORTF_BASE, GPIO_PIN_1|GPIO_PIN_2|GPIO_PIN_3);
GPIOPinWrite(GPIO_PORTF_BASE, GPIO_PIN_1|GPIO_PIN_2|GPIO_PIN_3, 0);

SysCtlPeripheralEnable(SYSCTL_PERIPH_TIMER0);
SysCtlDelay(3);
TimerConfigure(TIMER0_BASE, TIMER_CFG_A_PERIODIC);
TimerLoadSet(TIMER0_BASE, TIMER_A, 39999);   // for 1msec
IntMasterEnable();
TimerIntEnable(TIMER0_BASE, TIMER_TIMA_TIMEOUT);
IntEnable(INT_TIMER0A);
TimerEnable(TIMER0_BASE, TIMER_A);

while(1){

}
}

.............................................................................................................................

............................ cstartup_M.c .........................................................................

/**************************************************
*
* This file contains an interrupt vector for Cortex-M written in C.
* The actual interrupt functions must be provided by the application developer.
*
* Copyright 2007 IAR Systems. All rights reserved.
*
* $Revision: 66254 $
*
**************************************************/

#pragma language=extended
#pragma segment="CSTACK"

extern void __iar_program_start( void );

extern void NMI_Handler( void );
extern void HardFault_Handler( void );
extern void MemManage_Handler( void );
extern void BusFault_Handler( void );
extern void UsageFault_Handler( void );
extern void SVC_Handler( void );
extern void DebugMon_Handler( void );
extern void PendSV_Handler( void );
extern void SysTick_Handler( void );

//...........................................................
extern void TIMER0A_Handler( void );      //************
//...........................................................
typedef void( *intfunc )( void );
typedef union { intfunc __fun; void * __ptr; } intvec_elem;

// The vector table is normally located at address 0.
// When debugging in RAM, it can be located in RAM, aligned to at least 2^6.
// If you need to define interrupt service routines,
// make a copy of this file and include it in your project.
// The name "__vector_table" has special meaning for C-SPY, which
// is where to find the SP start value.
// If vector table is not located at address 0, the user has to initialize
// the NVIC vector table register (VTOR) before using interrupts.

#pragma location = ".intvec"
const intvec_elem __vector_table[] =
{
{ .__ptr = __sfe( "CSTACK" ) },
__iar_program_start,

NMI_Handler,
HardFault_Handler,
MemManage_Handler,
BusFault_Handler,
UsageFault_Handler,
0,
0,
0,
0,
SVC_Handler,
DebugMon_Handler,
0,
PendSV_Handler,
SysTick_Handler,
//...........................................................
0,
0,
0,
0,
0,
0,
0,
0,
0,
0,
0,
0,
0,
0,
0,
0,
0,
0,
0,
TIMER0A_Handler                                      //************
//...........................................................
};

#pragma call_graph_root = "interrupt"
__weak void NMI_Handler( void ) { while (1) {} }
#pragma call_graph_root = "interrupt"
__weak void HardFault_Handler( void ) { while (1) {} }
#pragma call_graph_root = "interrupt"
__weak void MemManage_Handler( void ) { while (1) {} }
#pragma call_graph_root = "interrupt"
__weak void BusFault_Handler( void ) { while (1) {} }
#pragma call_graph_root = "interrupt"
__weak void UsageFault_Handler( void ) { while (1) {} }
#pragma call_graph_root = "interrupt"
__weak void SVC_Handler( void ) { while (1) {} }
#pragma call_graph_root = "interrupt"
__weak void DebugMon_Handler( void ) { while (1) {} }
#pragma call_graph_root = "interrupt"
__weak void PendSV_Handler( void ) { while (1) {} }
#pragma call_graph_root = "interrupt"
__weak void SysTick_Handler( void ) { while (1) {} }

//...........................................................
#pragma call_graph_root = "interrupt"
__weak void TIMER0A_Handler( void ) { while (1) {} }    //************
//...........................................................

void __cmain( void );
__weak void __iar_init_core( void );
__weak void __iar_init_vfp( void );

#pragma required=__vector_table
void __iar_program_start( void )
{
__iar_init_core();
__iar_init_vfp();
__cmain();
}

.............................................................................................................................