// Interrupt handlers.
void TimerInterrupt()
{
  (*timer_function)(); // Call timer callback function.
  Timer3Clear = 0x0; // Clear timer 3 interrupt line.
}

// IRQ interrupt handler.
// Only the timer interrupt is used by this example.
__irq __arm void irq_handler(void)
{
  void (*interrupt_function)();
  unsigned int vector;
  // Called at 1000 Hz rate.
  vector = VIC2VectAddr; // Get interrupt vector.
  interrupt_function = (void(*)())vector;
  (*interrupt_function)(); // Call vectored interrupt function.
  VIC2VectAddr = 0; // Clear interrupt in VIC.
}

// Interrupt functions.
void EP9312InitInterrupt(void(*timer_func)())
{
  // Setup timer callback function.
  timer_function = timer_func;

  // Setup interrupt controller.
  VIC1Protection = 0;
  VIC2Protection = 0;
  // Disable all interrupts
  VIC1IntEnClear = 0xffffffff;
  VIC2IntEnClear = 0xffffffff;

  VIC2IntSelect &= ~TC3OI_bit; // IRQ on timer 3 line.
  VIC2VectAddr0 = (unsigned int)&TimerInterrupt;
  VIC2VectCntl0 = 0x20 | VIC2_TC3OI; // Enable vector interrupt for timer 3.
  VIC2IntEnable |= TC3OI_bit; // Enable timer 3 interrupt.

  VIC2IntSelect &= ~TC39OI_bit; // IRQ on MAC line.
  VIC2VectAddr1 = (unsigned int)&InterruptMac;
  VIC2VectCntl1 = 0x20 | VIC2_INT_MAC; // Enable vector interrupt for MAC.
  VIC2IntEnable |= TC39OI_bit; // Enable MAC interrupt.
}

;-----------------------------------------------------------------------------
; This file contains the startup code used by the ICCARM C compiler.
;
; The modules in this file are included in the libraries, and may be replaced
; by any user-defined modules that define the PUBLIC symbol _program_start or
; a user defined start symbol.
; To override the cstartup defined in the library, simply add your modified
; version to the workbench project.
;
; All code in the modules (except ?RESET) will be placed in the ICODE segment.
;
; $Revision: 1.2 $
;
;-----------------------------------------------------------------------------
    
;
; Naming covention of labels in this file:
;
;  ?xxx      - External labels only accessed from assembler.
;  __xxx  - External labels accessed from or defined in C.
;  xxx      - Labels local to one module (note: this file contains
;           several modules).
;  main      - The starting point of the user program.
;

;---------------------------------------------------------------
; Macros and definitions for the whole file
;---------------------------------------------------------------

; Mode, correspords to bits 0-5 in CPSR
MODE_BITS    DEFINE    0x1F    ; Bit mask for mode bits in CPSR
USR_MODE    DEFINE    0x10    ; User mode
FIQ_MODE    DEFINE    0x11    ; Fast Interrupt Request mode
IRQ_MODE    DEFINE    0x12    ; Interrupt Request mode
SVC_MODE    DEFINE    0x13    ; Supervisor mode
ABT_MODE    DEFINE    0x17    ; Abort mode
UND_MODE    DEFINE    0x1B    ; Undefined Instruction mode
SYS_MODE    DEFINE    0x1F    ; System mode
    
;---------------------------------------------------------------
; ?RESET
; Reset Vector.
; Normally, segment INTVEC is linked at address 0.
; For debugging purposes, INTVEC may be placed at other
; addresses.
; A debugger that honors the entry point will start the
; program in a normal way even if INTVEC is not at address 0.
;---------------------------------------------------------------

        MODULE    ?RESET
        COMMON    INTVEC:CODE:NOROOT(2)
        PUBLIC  __program_start
        EXTERN    ?cstartup
;        EXTERN    undef_handler, swi_handler, prefetch_handler
;        EXTERN    data_handler, fiq_handler
        EXTERN    irq_handler
        CODE32; Always ARM mode after reset    
        org    0x00
__program_start
        ldr    pc,=?cstartup ; Absolute jump can reach 4 GByte
;        ldr    b,?cstartup   ; Relative branch allows remap, limited to 32 MByte
        org    0x04
undef_handler    ldr    pc,=undef_handler
        org    0x08
swi_handler    ldr    pc,=swi_handler
        org    0x0c
prefetch_handler ldr    pc,=prefetch_handler
        org    0x10
data_handler    ldr    pc,=data_handler
        org    0x18
        ldr    pc,=irq_handler
        org    0x1c
fiq_handler    ldr    pc,=fiq_handler

    ; Constant table entries (for ldr pc) will be placed at 0x20
        org    0x20
        LTORG
;        ENDMOD    __program_start
                ENDMOD

;---------------------------------------------------------------
; ?CSTARTUP
;---------------------------------------------------------------
        MODULE    ?CSTARTUP

        RSEG    IRQ_STACK:DATA(2)
        RSEG    SVC_STACK:DATA:NOROOT(2)
        RSEG    CSTACK:DATA(2)
        RSEG    ICODE:CODE:NOROOT(4)
        PUBLIC    ?cstartup
        EXTERN    ?main

; Execution starts here.
; After a reset, the mode is ARM, Supervisor, interrupts disabled.

        CODE32
?cstartup

; Add initialization nedded before setup of stackpointers here


; Initialize the stack pointers.
; The pattern below can be used for any of the exception stacks:
; FIQ, IRQ, SVC, ABT, UND, SYS.
; The USR mode uses the same stack as SYS.
; The stack segments must be defined in the linker command file,
; and be declared above.
                mrs     r0,cpsr                            ; Original PSR value
                bic     r0,r0,#MODE_BITS                   ; Clear the mode bits
                orr     r0,r0,#IRQ_MODE                    ; Set IRQ mode bits
                msr     cpsr_c,r0                          ; Change the mode
                ldr     sp,=SFE(IRQ_STACK) & 0xFFFFFFF8    ; End of IRQ_STACK

                bic     r0,r0,#MODE_BITS                   ; Clear the mode bits
                orr     r0,r0,#SYS_MODE                    ; Set System mode bits
                msr     cpsr_c,r0                          ; Change the mode
                ldr     sp,=SFE(CSTACK) & 0xFFFFFFF8       ; End of CSTACK

#ifdef __ARMVFP__
; Enable the VFP coprocessor.
                mov     r0, #0x40000000                ; Set EN bit in VFP
                fmxr    fpexc, r0                      ; FPEXC, clear others.

; Disable underflow exceptions by setting flush to zero mode.
; For full IEEE 754 underflow compliance this code should be removed
; and the appropriate exception handler installed.
                mov     r0, #0x01000000               ; Set FZ bit in VFP
                fmxr    fpscr, r0                      ; FPSCR, clear others.
#endif

; Add more initialization here

; Continue to ?main for more IAR specific system startup

                ldr     r0,=?main
                bx      r0

                LTORG
                ENDMOD
                END

00000010: 18 F0 9F E5 00 00 00 00  18 F0 9F E5 18 F0 9F E5  |................|
                                   ^^^^^^^^^^^

   18:    e59ff018     ldr    pc, [pc, #18]; 0x38

unsigned int old_0x38;
unsigned int *ptr_0x38=(unsigned int *)0x38;

old_0x38= *ptr_0x38;
*ptr_0x38 = (unsigned int)irq_handler;