一、串口低功耗模式介绍
1.1 介绍
+ B! f; m. ?; r' u6 o6 g7 Gstm32可以通过串口来从stop模式唤醒，如果基于hal库，只要进行一些配置就能使用，这种通过串口唤醒的低功耗模式可以用在带电池的设备上，在需要设备工作的时候才将其唤醒处理事务，处理完后进入stop模式降低功耗。

% k! Y. \. M1 E1.2 三种模式和相关的寄存器
1.2.1 寄存器
: P- b. L6 E2 ~1.2.1.1 CR3[21:20] WUS[1:0]
- k$ \8 n/ d) F: n功能：选择从低功耗模式中断唤醒的标志
* t/ t( |, x9 E$ U3 i配置说明：
' N- n# J; `/ o0 d' b  n- n7 H, q00：地址匹配模式
7 |+ B! p! M7 p01：保留
10：检测起始位
& ~4 {! _3 S# Q; l11：RXNE/RXFNE中断
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- T9 K( `) @: P1.2.1.2 CR3[22] WUFIE
! X; \) n4 S* D5 k2 _1 f功能：使能从低功耗模式唤醒
配置说明：
0：关闭中断
1：使能WUF中断，即当ISR的WUF为1时产生一个中断

$ s8 ?8 s- ?( X, L9 g1.2.1.3 CR1[1] UESM
- k% e9 g( v# ~  S' Y. o功能：使能串口的低功耗模式
配置说明：
- f4 ^$ }- H9 g1 |% y9 }; ~0：串口不能唤醒低功耗模式
. L2 q4 _% i4 {4 D1：串口能唤醒低功耗模式

% H/ p* B: I) S0 u& r3 o1.2.1.4 PWR_CR1[2:0] LPMS[2:0]
功能：低功耗模式选择
配置说明：
2 `# m+ H. s3 v" Z& \000：stop 0模式
1 {/ ]. S- c5 N- Z  u! {001：stop1模式
010：保留
011：stanby模式
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1.2.1.5 SCB_SCR[2] SLEEPDEEP
功能：决定处理器在低功耗模式时选择睡眠模式还是深度睡眠模式，SCB寄存器的内容在m0+编程手册里。
配置说明：
0：睡眠模式
1：深度睡眠模式

1.2.2 模式
4 h, N* T" D% ]0 m地址匹配模式
检测起始位
RXNE/RXFNE中断模式
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6 [& q8 c8 @7 P9 M二、用法
6 _/ R5 K* T8 o7 h, t: c" `( b7 B2.1 地址匹配模式
地址配置成0x29（0010 1001），串口需要发送0xa9来唤醒，唤醒后需要关闭唤醒中断使能，重新初始化时钟。

1. /* make sure that no LPUART transfer is on-going */
   
2.   while (__HAL_UART_GET_FLAG(&hlpuart1, USART_ISR_BUSY) == SET);
   
3. 
   
4.   /* make sure that LPUART is ready to receive
   
5.    * (test carried out again later in HAL_UARTEx_StopModeWakeUpSourceConfig) */
   
6.   while (__HAL_UART_GET_FLAG(&hlpuart1, USART_ISR_REACK) == RESET);
   
7. 
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8.   /* set the wake-up event:
   
9.    * specify address-to-match type.
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10.    * The address is 0x29, meaning the character triggering the
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11.    * address match is 0xA9 */
    
12.   WakeUpSelection.WakeUpEvent   = UART_WAKEUP_ON_ADDRESS;
    
13.   WakeUpSelection.AddressLength = UART_ADDRESS_DETECT_7B;
    
14.   WakeUpSelection.Address       = 0x29;
    
15.   if (HAL_UARTEx_StopModeWakeUpSourceConfig(&hlpuart1, WakeUpSelection) != HAL_OK)
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16.   {
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17.     Error_Handler();
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18.   }
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19. 
    
20.   /* Enable the LPUART Wake UP from stop mode Interrupt */
    
21.   __HAL_UART_ENABLE_IT(&hlpuart1, UART_IT_WUF);
    
22. 
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23.   /* about to enter stop mode: switch off LED1 */
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24.   BSP_LED_Off(LED1);
    
25.   /* enable MCU wake-up by LPUART */
    
26.   HAL_UARTEx_EnableStopMode(&hlpuart1);
    
27.   /* enter STOP mode */
    
28.   HAL_PWR_EnterSTOPMode(PWR_LOWPOWERREGULATOR_ON, PWR_STOPENTRY_WFI);
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29. 
    
30.   /* ... STOP mode ... */
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31. 
    
32. 
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33.   /* at that point, MCU has been awoken: LED1 has been turned back on */
    
34.   SystemClock_Config_fromSTOP();
    
35. 
    
36.   /* Wake Up on 7-bit address detection successful */
    
37.   HAL_UARTEx_DisableStopMode(&hlpuart1);

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2.2 起始位模式
串口上产生一个起始位可以唤醒。

1. /* make sure that no LPUART transfer is on-going */
   
2.   while (__HAL_UART_GET_FLAG(&hlpuart1, USART_ISR_BUSY) == SET);
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3. 
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4.   /* make sure that LPUART is ready to receive
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5.    * (test carried out again later in HAL_UARTEx_StopModeWakeUpSourceConfig) */
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6.   while (__HAL_UART_GET_FLAG(&hlpuart1, USART_ISR_REACK) == RESET);
   
7. 
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8.   /* set the wake-up event:
   
9.    * specify wake-up on start-bit detection */
   
10.   WakeUpSelection.WakeUpEvent = UART_WAKEUP_ON_STARTBIT;
    
11.   if (HAL_UARTEx_StopModeWakeUpSourceConfig(&hlpuart1, WakeUpSelection) != HAL_OK)
    
12.   {
    
13.     Error_Handler();
    
14.   }
    
15. 
    
16.   /* Enable the LPUART Wake UP from STOP mode Interrupt */
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17.   __HAL_UART_ENABLE_IT(&hlpuart1, UART_IT_WUF);
    
18. 
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19.   /* about to enter STOP mode: switch off LED1 */
    
20.   BSP_LED_Off(LED1);
    
21.   /* enable MCU wake-up by LPUART */
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22.   HAL_UARTEx_EnableStopMode(&hlpuart1);
    
23.   /* enter STOP mode */
    
24.   HAL_PWR_EnterSTOPMode(PWR_LOWPOWERREGULATOR_ON, PWR_STOPENTRY_WFI);
    
25. 
    
26.   /* ... STOP mode ... */
    
27. 
    
28. 
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29.   /* at that point, MCU has been awoken: LED1 has been turned back on */
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30.   SystemClock_Config_fromSTOP();
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31. 
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32.   /* Wake Up on start bit detection successful */
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33.   HAL_UARTEx_DisableStopMode(&hlpuart1);

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2 z/ X6 B7 l' U0 x0 r8 X4 i2.3 RXNE/RXFNE中断模式
接收到一个字符可以唤醒，接收的字节是完整的。
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1. /* make sure that no LPUART transfer is on-going */
   
2.   while (__HAL_UART_GET_FLAG(&hlpuart1, USART_ISR_BUSY) == SET);
   
3.   /* make sure that LPUART is ready to receive
   
4.    * (test carried out again later in HAL_UARTEx_StopModeWakeUpSourceConfig) */
   
5.   while (__HAL_UART_GET_FLAG(&hlpuart1, USART_ISR_REACK) == RESET);
   
6. 
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7.   /* set the wake-up event:
   
8.    * specify wake-up on RXNE flag */
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9.   WakeUpSelection.WakeUpEvent = UART_WAKEUP_ON_READDATA_NONEMPTY;
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10.   if (HAL_UARTEx_StopModeWakeUpSourceConfig(&hlpuart1, WakeUpSelection) != HAL_OK)
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11.   {
    
12.     Error_Handler();
    
13.   }
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14. 
    
15.   /* Enable the UART Wake UP from STOP mode Interrupt */
    
16.   __HAL_UART_ENABLE_IT(&hlpuart1, UART_IT_WUF);
    
17. 
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18.   /* about to enter STOP mode: switch off LED1 */
    
19.   BSP_LED_Off(LED1);
    
20.   /* enable MCU wake-up by LPUART */
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21.   HAL_UARTEx_EnableStopMode(&hlpuart1);
    
22.   /* enter STOP mode */
    
23.   HAL_PWR_EnterSTOPMode(PWR_LOWPOWERREGULATOR_ON, PWR_STOPENTRY_WFI);
    
24. 
    
25.   /* ... STOP mode ... */
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26. 
    
27. 
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28.   /* at that point, MCU has been awoken: LED1 has been turned back on */
    
29.   SystemClock_Config_fromSTOP();
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30. 
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31.   /* Wake Up based on RXNE flag successful */
    
32.   HAL_UARTEx_DisableStopMode(&hlpuart1);

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三、注意事项
如果使用地址匹配模式，需要关闭RXNE的中断。
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1. 
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2. __HAL_UART_DISABLE_IT(&huart1,UART_IT_RXNE);

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