一、串口低功耗模式介绍
3 T* q1 V( g  P$ i) ?7 f1.1 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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& P$ i: b9 k/ {& z2 f1.2 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]
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配置说明：
00：地址匹配模式
9 R3 J( v# w! u0 J' I$ I01：保留
( t) W" m; f/ d9 a! T+ \10：检测起始位
4 _( k. X3 J4 L6 S/ u5 i11：RXNE/RXFNE中断
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1.2.1.2 CR3[22] WUFIE
功能：使能从低功耗模式唤醒
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1 d( U6 ]' |5 K0：关闭中断
. U! f' N4 R% U1 e9 `# \- n1：使能WUF中断，即当ISR的WUF为1时产生一个中断

: H% m- X/ M; c% w  A' J! T1.2.1.3 CR1[1] UESM
3 s4 f7 x5 o0 A( v1 {功能：使能串口的低功耗模式
7 }7 V; n3 r( `. D配置说明：
0：串口不能唤醒低功耗模式
1：串口能唤醒低功耗模式

& v: a+ z% ~2 Y3 u1.2.1.4 PWR_CR1[2:0] LPMS[2:0]
6 G6 o# D$ N4 M0 A功能：低功耗模式选择
( h6 E* W! t' S* v6 S8 x: u配置说明：
' [+ \) f5 f* E1 p000：stop 0模式
5 w" v9 Q7 ^% [4 I+ s" P4 I001：stop1模式
- X8 O) W; y) A) b- K- y$ k010：保留
011：stanby模式
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9 z! N( c5 d5 T7 g" V& k' q8 p1.2.1.5 SCB_SCR[2] SLEEPDEEP
/ w) B! c8 V4 b: X) c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。
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1 U  f. C- {5 e% \  e8 N0：睡眠模式
1：深度睡眠模式
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! P$ \$ S( O7 D0 E. a1.2.2 模式
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检测起始位
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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
   
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);
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7. 
   
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
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11.    * address match is 0xA9 */
    
12.   WakeUpSelection.WakeUpEvent   = UART_WAKEUP_ON_ADDRESS;
    
13.   WakeUpSelection.AddressLength = UART_ADDRESS_DETECT_7B;
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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();
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18.   }
    
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);
    
29. 
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30.   /* ... STOP mode ... */
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31. 
    
32. 
    
33.   /* at that point, MCU has been awoken: LED1 has been turned back on */
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34.   SystemClock_Config_fromSTOP();
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35. 
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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. 
   
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);
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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;
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11.   if (HAL_UARTEx_StopModeWakeUpSourceConfig(&hlpuart1, WakeUpSelection) != HAL_OK)
    
12.   {
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13.     Error_Handler();
    
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);
    
18. 
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19.   /* about to enter STOP mode: switch off LED1 */
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20.   BSP_LED_Off(LED1);
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21.   /* enable MCU wake-up by LPUART */
    
22.   HAL_UARTEx_EnableStopMode(&hlpuart1);
    
23.   /* enter STOP mode */
    
24.   HAL_PWR_EnterSTOPMode(PWR_LOWPOWERREGULATOR_ON, PWR_STOPENTRY_WFI);
    
25. 
    
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 */
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30.   SystemClock_Config_fromSTOP();
    
31. 
    
32.   /* Wake Up on start bit detection successful */
    
33.   HAL_UARTEx_DisableStopMode(&hlpuart1);

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& c! u9 I1 p9 A8 h( n2.3 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);
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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) */
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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)
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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 */
    
21.   HAL_UARTEx_EnableStopMode(&hlpuart1);
    
22.   /* enter STOP mode */
    
23.   HAL_PWR_EnterSTOPMode(PWR_LOWPOWERREGULATOR_ON, PWR_STOPENTRY_WFI);
    
24. 
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25.   /* ... STOP mode ... */
    
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. 
    
31.   /* Wake Up based on RXNE flag successful */
    
32.   HAL_UARTEx_DisableStopMode(&hlpuart1);

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! z" E4 d: }$ S# \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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