ARM, RISC-V контроллеры

IAR 4.1 и ISR проблема Сконфигурировал UART1 для генерации сообщений по U1THRE. Но при отладке не вызывается обработчик ISR. Что тут может быть не правильно? startup.s79

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

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
	
		MODULE	?RESET
		COMMON	INTVEC:CODE:NOROOT(2)
		PUBLIC  __program_start
		EXTERN	?cstartup
		EXTERN	irq_handler
		CODE32	; Always ARM mode after reset	
		org	0x00
__program_start
		ldr	pc,=?cstartup  ; Absolute jump can reach 4 GByte
		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

		MODULE	?CSTARTUP

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

		CODE32
?cstartup

                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

                ldr     r0,=?main        
                bx      r0        
            
                LTORG
                ENDMOD
                END

main.c

#include 
#include 
#include 
#include "iolpc210x.h"

//XTAL frequency in Hz
#define XTALFREQ 14745600

//pclk must always be XTALFREQ/4 when using the ROM monitor.
#define PCLKFREQ (XTALFREQ/4)
#define BAUDRATE    9600
#define BAUDRATEDIVISOR (PCLKFREQ/(BAUDRATE*16))


// IRQ exception handler. Calls the interrupt handlers.
__irq __arm void irq_handler(void)
{
  void (*interrupt_function)();
  unsigned int vector;

  vector = VICVectAddr;   // Get interrupt vector.
  interrupt_function = (void(*)())vector;
  (*interrupt_function)();  // Call vectored interrupt function.

  VICVectAddr = 0;        // Clear interrupt in VIC.
}

//Dummy interrupt handler, called as default in irqHandler() if no other
//vectored interrupt is called.
static void DefDummyInterrupt()
{
}

//UART1 interrupt handler
static void UART1Interrupt()
{
}

void main(void)
{
  MEMMAP = 2;
	
  //Set pins for use with UART
  PINSEL0_bit.P0_8=0x1; // Set pin function to TxD (UART1)
  PINSEL0_bit.P0_9=0x1; // Set pin function to RxD (UART1)

  //Set the FIFO enable bit in the FCR register. This bit must be set for
  //proper UART operation.
  U1FCR_bit.FCRFE = 1;

  //Set baudrate
  U1LCR_bit.DLAB = 1;
  U1DLL = BAUDRATEDIVISOR & 0x00ff;
  U1DLM = (BAUDRATEDIVISOR >> 8) & 0x00ff;
  U1LCR_bit.DLAB = 0;

  //Set mode
  U1LCR_bit.WLS = 0x3;   //8 bit word length
  U1LCR_bit.SBS = 0x0;   //1 stop bit
  U1LCR_bit.PE  = 0x0;   //No parity

  //Enable UART1 interrupts
  U1IER_bit.RDAIE  = 0;  //Enable byte received interrupt
  U1IER_bit.THREIE = 1;  //Enable tx buf empty interrupt	
  
  __disable_interrupt();

  // Setup interrupt controller.
  VICProtection = 0;
  VICIntEnClear = 0xffffffff;
  VICSoftIntClear = 0xffffffff;
  VICDefVectAddr = (unsigned int)&DefDummyInterrupt;  
  VICIntSelect &= ~(1<