一、串口低功耗模式介绍
1.1 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。

1.2 三种模式和相关的寄存器
1.2.1 寄存器
1.2.1.1 CR3[21:20] WUS[1:0]
5 R3 i/ A- A0 C3 [# A' B; E功能：选择从低功耗模式中断唤醒的标志
配置说明：
5 t+ a5 \. @1 p5 v4 ]00：地址匹配模式
) L/ A& x, G( b% d2 f" U! }01：保留
0 I8 s3 b4 T3 Y10：检测起始位
; Y4 ^) `$ l; z! N7 }% l  ^11：RXNE/RXFNE中断

1.2.1.2 CR3[22] WUFIE
功能：使能从低功耗模式唤醒
, X/ D. A& h( x4 |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
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1.2.1.3 CR1[1] UESM
功能：使能串口的低功耗模式
配置说明：
0：串口不能唤醒低功耗模式
/ i- @7 i7 N1 H0 {. }! L5 }1：串口能唤醒低功耗模式
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1 n& @; H" N( D, P: i1.2.1.4 PWR_CR1[2:0] LPMS[2:0]
( S, `5 z6 \: w功能：低功耗模式选择
: h3 V: C! n. _# I0 `配置说明：
8 C6 o  }! }, [3 d6 _$ D8 W000：stop 0模式
001：stop1模式
) ~% F# G0 o5 Q0 D, x7 ^010：保留
1 z2 i( o) k* j; f011：stanby模式

( k  W! {) s7 h5 x5 B  M1.2.1.5 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

8 U6 \, X1 l6 q4 }1.2.2 模式
8 g/ Z$ ^  N, m+ M地址匹配模式
检测起始位
RXNE/RXFNE中断模式
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6 k4 O' ~2 C" p% P3 \二、用法
2.1 地址匹配模式
& P. v/ g9 ?' A% m5 o: j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 */
   
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:
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9.    * specify address-to-match type.
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10.    * The address is 0x29, meaning the character triggering the
    
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;
    
15.   if (HAL_UARTEx_StopModeWakeUpSourceConfig(&hlpuart1, WakeUpSelection) != HAL_OK)
    
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 */
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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 */
    
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. 
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32. 
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33.   /* at that point, MCU has been awoken: LED1 has been turned back on */
    
34.   SystemClock_Config_fromSTOP();
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35. 
    
36.   /* Wake Up on 7-bit address detection successful */
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37.   HAL_UARTEx_DisableStopMode(&hlpuart1);

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/ T6 H( n0 c- F6 o2.2 起始位模式
" w% k8 c3 d9 ?& A; A+ n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);
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3. 
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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);
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7. 
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8.   /* set the wake-up event:
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9.    * specify wake-up on start-bit detection */
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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.   {
    
13.     Error_Handler();
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14.   }
    
15. 
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16.   /* Enable the LPUART Wake UP from STOP mode Interrupt */
    
17.   __HAL_UART_ENABLE_IT(&hlpuart1, UART_IT_WUF);
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18. 
    8 h+ W1 B9 [# t0 x4 \, \- H+ ]
19.   /* about to enter STOP mode: switch off LED1 */
    
20.   BSP_LED_Off(LED1);
    
21.   /* enable MCU wake-up by LPUART */
    
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);
    
25. 
    
26.   /* ... STOP mode ... */
    8 d8 Z* M: O# ?, \
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();
    
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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4 F% Q7 p  l: t2.3 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 */
   4 g& Z  }1 Y% h9 P* n0 z$ P' f6 ~* Q
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) */
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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 */
   
9.   WakeUpSelection.WakeUpEvent = UART_WAKEUP_ON_READDATA_NONEMPTY;
   
10.   if (HAL_UARTEx_StopModeWakeUpSourceConfig(&hlpuart1, WakeUpSelection) != HAL_OK)
    
11.   {
    
12.     Error_Handler();
    % n  o$ x! C. N, _/ \2 I# x0 q
13.   }
    
14. 
    
15.   /* Enable the UART Wake UP from STOP mode Interrupt */
    
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 */
    + |# E3 \6 _# o7 y: o9 {- I
21.   HAL_UARTEx_EnableStopMode(&hlpuart1);
    
22.   /* enter STOP mode */
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23.   HAL_PWR_EnterSTOPMode(PWR_LOWPOWERREGULATOR_ON, PWR_STOPENTRY_WFI);
    
24. 
    
25.   /* ... STOP mode ... */
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26. 
    0 q/ Q) }% k; t( ]( H  Y
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();
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30. 
    
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。

1. 
   % W/ V3 a0 L- \3 i" z
2. __HAL_UART_DISABLE_IT(&huart1,UART_IT_RXNE);

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