一、串口低功耗模式介绍
* q& t, b7 [: |. u3 E1.1 介绍
stm32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。
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* Z& A4 Q" B$ _5 u  s1.2 三种模式和相关的寄存器
1.2.1 寄存器
1 j& A8 n( l! U! s1.2.1.1 CR3[21:20] WUS[1:0]
功能：选择从低功耗模式中断唤醒的标志
% ^& q3 D; x9 ?配置说明：
00：地址匹配模式
01：保留
( x" r  r9 J( x0 m& t10：检测起始位
11：RXNE/RXFNE中断

  e0 i* ?# v, L) y1.2.1.2 CR3[22] WUFIE
1 k# C- Y. g% S6 }功能：使能从低功耗模式唤醒
配置说明：
, E9 y. K, t$ p. m$ x8 ~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
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1.2.1.3 CR1[1] UESM
" q8 E1 h4 J: n( r) W6 m8 }* \5 s功能：使能串口的低功耗模式
配置说明：
) n2 H9 N4 \: o& Z0：串口不能唤醒低功耗模式
1：串口能唤醒低功耗模式

7 V5 ^. j0 S' s1 h8 q1.2.1.4 PWR_CR1[2:0] LPMS[2:0]
/ _' q8 x4 `& k7 E功能：低功耗模式选择
% z5 [! S8 ]8 v( [. Z7 B  _2 z配置说明：
000：stop 0模式
- ^# y1 i* o3 R+ {001：stop1模式
7 B# h! n1 V4 E0 ?9 L010：保留
, z& M: x$ R* U" f4 Q+ j, h7 b3 m/ v011：stanby模式
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0 C* l  W" }+ z& v7 w  H1 x1.2.1.5 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。
* i7 Y, F- g* E6 k3 s$ @2 K配置说明：
9 a! H& I# M/ B0 H9 V7 v4 x0：睡眠模式
1：深度睡眠模式
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; B$ D6 s1 \9 x6 ?1.2.2 模式
3 v2 k4 r: a; O" [$ e地址匹配模式
检测起始位
7 Q" A( Y3 Z: _6 x# L! hRXNE/RXFNE中断模式

二、用法
2.1 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。
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1. /* make sure that no LPUART transfer is on-going */
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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) */
   
6.   while (__HAL_UART_GET_FLAG(&hlpuart1, USART_ISR_REACK) == RESET);
   
7. 
   
8.   /* set the wake-up event:
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9.    * specify address-to-match type.
   
10.    * The address is 0x29, meaning the character triggering the
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11.    * address match is 0xA9 */
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12.   WakeUpSelection.WakeUpEvent   = UART_WAKEUP_ON_ADDRESS;
    
13.   WakeUpSelection.AddressLength = UART_ADDRESS_DETECT_7B;
    
14.   WakeUpSelection.Address       = 0x29;
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15.   if (HAL_UARTEx_StopModeWakeUpSourceConfig(&hlpuart1, WakeUpSelection) != HAL_OK)
    
16.   {
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17.     Error_Handler();
    
18.   }
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19. 
    
20.   /* Enable the LPUART Wake UP from stop mode Interrupt */
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21.   __HAL_UART_ENABLE_IT(&hlpuart1, UART_IT_WUF);
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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 */
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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 */
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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。
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1. /* make sure that no LPUART transfer is on-going */
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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) */
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6.   while (__HAL_UART_GET_FLAG(&hlpuart1, USART_ISR_REACK) == RESET);
   
7. 
   
8.   /* set the wake-up event:
   
9.    * specify wake-up on start-bit detection */
   
10.   WakeUpSelection.WakeUpEvent = UART_WAKEUP_ON_STARTBIT;
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11.   if (HAL_UARTEx_StopModeWakeUpSourceConfig(&hlpuart1, WakeUpSelection) != HAL_OK)
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12.   {
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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);
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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);
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23.   /* enter STOP mode */
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24.   HAL_PWR_EnterSTOPMode(PWR_LOWPOWERREGULATOR_ON, PWR_STOPENTRY_WFI);
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25. 
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26.   /* ... STOP mode ... */
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27. 
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28. 
    
29.   /* at that point, MCU has been awoken: LED1 has been turned back on */
    
30.   SystemClock_Config_fromSTOP();
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31. 
    
32.   /* Wake Up on start bit detection successful */
    
33.   HAL_UARTEx_DisableStopMode(&hlpuart1);

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" P7 B. G) {+ q2 v! w2.3 RXNE/RXFNE中断模式
! u8 d2 W, e' P2 @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);
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3.   /* make sure that LPUART is ready to receive
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4.    * (test carried out again later in HAL_UARTEx_StopModeWakeUpSourceConfig) */
   
5.   while (__HAL_UART_GET_FLAG(&hlpuart1, USART_ISR_REACK) == RESET);
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6. 
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7.   /* set the wake-up event:
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8.    * specify wake-up on RXNE flag */
   
9.   WakeUpSelection.WakeUpEvent = UART_WAKEUP_ON_READDATA_NONEMPTY;
   
10.   if (HAL_UARTEx_StopModeWakeUpSourceConfig(&hlpuart1, WakeUpSelection) != HAL_OK)
    
11.   {
    
12.     Error_Handler();
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13.   }
    
14. 
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15.   /* Enable the UART Wake UP from STOP mode Interrupt */
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16.   __HAL_UART_ENABLE_IT(&hlpuart1, UART_IT_WUF);
    
17. 
    
18.   /* about to enter STOP mode: switch off LED1 */
    
19.   BSP_LED_Off(LED1);
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20.   /* enable MCU wake-up by LPUART */
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21.   HAL_UARTEx_EnableStopMode(&hlpuart1);
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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 */
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29.   SystemClock_Config_fromSTOP();
    
30. 
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31.   /* Wake Up based on RXNE flag successful */
    
32.   HAL_UARTEx_DisableStopMode(&hlpuart1);

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; S1 K  V9 I  O* a- l  R3 i三、注意事项
如果使用地址匹配模式，需要关闭RXNE的中断。

1. 
   % z" ]& H  t8 c* L  }# o% N
2. __HAL_UART_DISABLE_IT(&huart1,UART_IT_RXNE);

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