STM32G030(SOP8) UART配置异常求助：TX引脚无数据输出

我正在尝试通过ARM汇编配置STM32G030（SOP8）的UART功能。目前外接LED可正常闪烁，说明循环逻辑正常；GDB显示寄存器值正确，但逻辑分析仪检测不到任何数据，TX引脚始终处于高电平状态。

当前寄存器数值 #

RCC_IOPENR = 0x00000003       @ GPIOA(UART) 和 GPIOB(LED)
RCC_APBENR2 = 0x00004000  
GPIOA_AFRH = 0x00000010  
GPIOA_MODER = 0xebfbffff  
USART_BRR = 0x00000683  
USART_CR1 = 0x00000009  
USART_CR2 = 0x00000000  
USART_CR3 = 0x00000000  
USART_ISR = 0x002000c0  

逻辑分析仪监测结果 #

• 通道1：LED正常闪烁
• STM32 TX引脚：预期输出连续的'A'，但实际始终处于高电平状态

请问我配置中存在什么问题？恳请各位提供帮助！

汇编代码 #

寄存器地址定义 #

.syntax unified
.cpu cortex-m0plus
.thumb

.word _StackEnd                 @       0x20000100
.word Reset_Handler             @       0x00000004
.space 0xb4  


.equ RCC, (0x40021000)
.equ RCC_IOPENR, (RCC + (0x34))
.equ RCC_APBENR2, (RCC + (0x40))        

.equ SYSCFG, (0x40010000)
.equ SYSCFG_CFGR1, (SYSCFG + (0x00))

.equ GPIOB, (0x50000400)
.equ GPIOB_MODER, (GPIOB + (0x00))
.equ GPIOB_BSRR, (GPIOB + (0x18))

.equ GPIOA, (0x50000000)                
.equ GPIOA_MODER, (GPIOA + (0x00))      
.equ GPIOA_AFRH, (GPIOA + (0x24))        

.equ USART1, (0x40013800)
.equ USART_CR1, (USART1 + (0x00))       
.equ USART_CR2, (USART1 + (0x04))       
.equ USART_CR3, (USART1 + (0x08))       
.equ USART_BRR, (USART1 + (0x0c))       
.equ USART_TDR, (USART1 + (0x28))       
.equ USART_ISR, (USART1 + (0x1c))       

UART配置代码 #

.text
.type Reset_Handler, %function
    Reset_Handler:

    ldr     r0, =RCC_IOPENR         @       (0x40021034)
    ldr     r2, [r0]                
    movs    r3, #0x1                @       0x1 用于GPIOA (UART1)
    orrs    r2, r2, r3              
    str     r2, [r0]                

    ldr     r0, =RCC_APBENR2        @       (0x40021040) UART时钟使能
    ldr     r2, [r0]                
    ldr     r3, =#0x4001            @   
    orrs    r2, r2, r3              
    str     r2, [r0]                

    ldr     r0, =SYSCFG_CFGR1       @       (0x40010000)
    ldr     r2, [r0]
    movs    r3, #0x8
    orrs    r2, r2, r3
    str     r2, [r0]

    ldr     r0, =GPIOA_AFRH         @       (0x50000024)
    ldr     r2, [r0]                
    ldr     r3, =#0x10              @       为PA9配置复用功能AF1 0x10
    orrs    r2, r2, r3              
    str     r2, [r0]

    ldr     r0, =GPIOA_MODER        @       (0x50000000)
    ldr     r2, [r0]                
    ldr     r3, =#0xfffbffff        @   为PA9开启复用模式       
    ands    r2, r2, r3              
    str     r2, [r0]

    ldr     r0, =USART_CR1          @       (0x40013800),
    movs    r3, #0x0                @
    str     r3, [r0]

    ldr     r0, =USART_BRR          @       (0x4001380c)
    ldr     r3, =#0x683             @       16MHz时钟，9600波特率
    str     r3, [r0]

    ldr     r0, =USART_CR2          @       (0x40013804),
    movs    r3, #0x0                @
    str     r3, [r0]

    ldr     r0, =USART_CR3          @   (0x40013808),
    movs    r3, #0x0                @
    str     r3, [r0]

    ldr     r0, =USART_CR1          @       (0x40013800),
    ldr     r2, [r0]
    movs    r3, #0x1               @       使能USART
    orrs    r2, r2, r3
    str     r2, [r0]

    ldr     r0, =USART_CR1          @       (0x40013800)
    ldr     r2, [r0]
    movs    r3, #0x8               @       使能发送器
    orrs    r2, r2, r3
    str     r2, [r0]
                              
teack_check:
    ldr     r0, =USART_ISR          @       (0x4001381c)
    ldr     r2, [r0]
    ldr     r3, =#0x200000          @       等待TEACK
    tst     r2, r3
    beq     teack_check

LED配置与主循环代码 #

ldr     r0, =RCC_IOPENR         @       (0x40021034)
    ldr     r2, [r0]                
    movs    r3, #0x2               @    0x2 用于GPIOB (LED)
    orrs    r2, r2, r3              
    str     r2, [r0]                

    ldr     r1, =GPIOB_MODER        @       (0x50000400)
    ldr     r4, [r1]                       
    ldr     r6, =#0xffff7fff        @       0xffff7fff 用于PB7 
    ands    r4, r4, r6              
    str     r4, [r1]                

blink_loop:

     txe_check:                             
             ldr     r1, =USART_ISR          @   (0x4001381c)
             ldr     r2, [r1]
             ldr     r3, =#0x80
             tst     r2, r3
             beq     txe_check

             ldr     r1, =USART_TDR          @       (0x40013828)
             movs    r3, #0x41              
             uxtb    r4, r3
             str     r4, [r1]

     tc_check:                              
             ldr     r1, =USART_ISR          @       (0x4001381c)
             ldr     r2, [r1]
             ldr     r3, =#0x40
             tst     r2, r3
             beq     tc_check


        ldr     r0, =GPIOB_BSRR         @   0x50000418
        ldr     r1, =#0x80          @   LED点亮
        str     r1, [r0]

        ldr     r2, =#10000000
    wait_1:
        subs    r2, #1
        bne     wait_1

        ldr     r1, =#0x800000          @   LED熄灭
        str     r1, [r0]

        ldr     r2, =#10000000
    wait_2:
        subs    r2, #1
        bne     wait_2

        b       blink_loop

内容的提问来源于stack exchange，提问作者michal