Why cortex m4 (stm32 discovery) usart3 is not working ??? (SOFTWARE)

Hello,

I have a problem,i wrote this program but it dosen't work.

It doesn't read its rx pin.

Can you help me pls ???

CODS:

PUBLIC MAINTASK
PUBLIC __vector_table
SECTION .text:CODE:REORDER(10)
;; Keep vector table even if it's not referenced
REQUIRE __vector_table
THUMB

BIT0 EQU 1 << 0
BIT1 EQU 1 << 1
BIT2 EQU 1 << 2
BIT3 EQU 1 << 3
BIT4 EQU 1 << 4
BIT5 EQU 1 << 5
BIT6 EQU 1 << 6
BIT7 EQU 1 << 7
BIT8 EQU 1 << 8
BIT9 EQU 1 << 9
BIT10 EQU 1 << 10
BIT11 EQU 1 << 11
BIT12 EQU 1 << 12
BIT13 EQU 1 << 13
BIT14 EQU 1 << 14
BIT15 EQU 1 << 15
BIT16 EQU 1 << 16
BIT17 EQU 1 << 17
BIT18 EQU 1 << 18
BIT19 EQU 1 << 19
BIT20 EQU 1 << 20
BIT21 EQU 1 << 21
BIT22 EQU 1 << 22
BIT23 EQU 1 << 23
BIT24 EQU 1 << 24
BIT25 EQU 1 << 25
BIT26 EQU 1 << 26
BIT27 EQU 1 << 27
BIT28 EQU 1 << 28
BIT29 EQU 1 << 29
BIT30 EQU 1 << 30
BIT31 EQU 1 << 31

RCC_BASE EQU 0x40023800
RCC_AHB1ENR EQU RCC_BASE + 0x30
RCC_APB1ENR EQU RCC_BASE + 0x40
RCC_CFGR EQU RCC_BASE + 0x08

GPIOD_BASE EQU 0x40020C00
GPIOD_MODER EQU GPIOD_BASE + 0x00
GPIOD_ODR EQU GPIOD_BASE + 0x14
GPIOD_IDR EQU GPIOD_BASE + 0x10
GPIOD_BSRR EQU GPIOD_BASE + 0x18
GPIOD_AFRH EQU GPIOD_BASE + 0x24

USART_SR EQU GPIOD_BASE + 0x00
USART_DR EQU GPIOD_BASE + 0x04
USART_BRR EQU GPIOD_BASE + 0x08
USART_CR1 EQU GPIOD_BASE + 0x0C

MAINTASK

LDR R0, =RCC_AHB1ENR 
LDR R1, [R0] 
ORR R1,R1,#BIT3
STR R1, [R0] 

LDR R0, =RCC_APB1ENR
LDR R1,[R0]
ORR R1,R1,#BIT18
str R1, [R0] 

LDR R0, =GPIOD_MODER 
LDR R1, =(BIT0|BIT2|BIT4|BIT6|BIT8|BIT10|BIT17|BIT19)
STR R1, [R0] 

LDR R0, =USART_CR1 
LDR R1, =(BIT13|BIT2|BIT3|BIT5) 
STR R1, [R0] 

LDR R0, =USART_BRR 
LDR R1, =0x341 ; BRAUD RATE 9600
STR R1, [R0] 

DATASTOCONTROL
LDR R2, =0x31 ;1 signal
LDR R3, =0x32 ;2 signal
LDR R4, =0x33 ;3 signal
LDR R5, =0x34 ;4 signal

CONTROLREAD

LDR R0, =USART_SR
LDR R1, [R0] 
MOVS R0, #BIT5 
TST R0, R1 
BEQ CONTROLREAD 

LDR R0, =USART_DR ; USART_DR(gelen veri) degerini R0'a yükle
LDR R1, [R0] ; USART_DR registerini R1'ye kopyala

MOVE

CMP R1, R2
BEQ FORWARD
CMP R1, R3
BEQ BACK
CMP R1, R4
BEQ RIGHT
CMP R1, R5
BEQ LEFT
BL CONTROLREAD

FORWARD
MOV R0,#0
MOV R1,#0
LDR R0,=GPIOD_ODR
MOV R1,#(BIT0|BIT2|BIT8|BIT10)
STR R1,[R0]
BL CONTROLREAD

BACK
MOV R0,#0
MOV R1,#0
LDR R0,=GPIOD_ODR
MOV R1,#(BIT4|BIT6|BIT8|BIT10)
STR R1,[R0]
BL CONTROLREAD

RIGHT
MOV R0,#0
MOV R1,#0
LDR R0,=GPIOD_ODR
MOV R1,#(BIT0|BIT6|BIT8|BIT10)
STR R1,[R0]
BL CONTROLREAD

LEFT
MOV R0,#0
MOV R1,#0
LDR R0,=GPIOD_ODR
MOV R1,#(BIT2|BIT4|BIT8|BIT10)
STR R1,[R0]
BL CONTROLREAD

;; Forward declaration of sections.

SECTION CSTACK:DATA:NOROOT(10)
SECTION .intvec:CODE:NOROOT(10)

DATA

__vector_table
DCD sfe(CSTACK)
DCD MAINTASK

DCD NMI_Handler
DCD HardFault_Handler
DCD MemManage_Handler
DCD BusFault_Handler
DCD UsageFault_Handler
DCD 0
DCD 0
DCD 0
DCD 0
DCD SVC_Handler
DCD DebugMon_Handler
DCD 0
DCD PendSV_Handler
DCD SysTick_Handler

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;
;; Default interrupt handlers.
;;

PUBWEAK NMI_Handler
PUBWEAK HardFault_Handler
PUBWEAK MemManage_Handler
PUBWEAK BusFault_Handler
PUBWEAK UsageFault_Handler
PUBWEAK SVC_Handler
PUBWEAK DebugMon_Handler
PUBWEAK PendSV_Handler
PUBWEAK SysTick_Handler

SECTION .text:CODE:REORDER:NOROOT(10)
THUMB

NMI_Handler
HardFault_Handler
MemManage_Handler
BusFault_Handler
UsageFault_Handler
SVC_Handler
DebugMon_Handler
PendSV_Handler
SysTick_Handler
Default_Handler
__default_handler
CALL_GRAPH_ROOT __default_handler, "interrupt"
NOCALL __default_handler
B __default_handler
BL MAINTASK
END