int main(void) { /*HW semaphore Clock enable*/ __HAL_RCC_HSEM_CLK_ENABLE(); /* Activate HSEM notification for Cortex-M4*/ HAL_HSEM_ActivateNotification(__HAL_HSEM_SEMID_TO_MASK(HSEM_ID_0)); /* Domain D2 goes to STOP mode (Cortex-M4 in deep-sleep) waiting for Cortex-M7 to perform system initialization (system clock config, external memory configuration.. ) */ HAL_PWREx_ClearPendingEvent(); HAL_PWREx_EnterSTOPMode(PWR_MAINREGULATOR_ON, PWR_STOPENTRY_WFE, PWR_D2_DOMAIN); /* Clear HSEM flag */ __HAL_HSEM_CLEAR_FLAG(__HAL_HSEM_SEMID_TO_MASK(HSEM_ID_0)); /* STM32H7xx HAL library initialization: - Systick timer is configured by default as source of time base, but user can eventually implement his proper time base source (a general purpose timer for example or other time source), keeping in mind that Time base duration should be kept 1ms since PPP_TIMEOUT_VALUEs are defined and handled in milliseconds basis. - Set NVIC Group Priority to 4 - Low Level Initialization */ HAL_Init(); /* Infinite loop */ while (1) { } }

这是一个C语言的程序，主要实现了STM32H7xx芯片的初始化和进入STOP模式。在进入STOP模式之前，需要先启用硬件信号量，并激活Cortex-M4的HSEM通知。进入STOP模式后，等待Cortex-M7进行系统初始化（包括系统时钟配置和外部内存配置等）。在程序的最后，使用了一个无限循环，即while(1)，使程序一直处于运行状态。

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请解释代码：int main(void) { /*HW semaphore Clock enable*/ __HAL_RCC_HSEM_CLK_ENABLE(); /* Activate HSEM notification for Cortex-M4*/ HAL_HSEM_ActivateNotification(__HAL_HSEM_SEMID_TO_MASK(HSEM_ID_0)); /* Domain D2 goes to STOP mode (Cortex-M4 in deep-sleep) waiting for Cortex-M7 to perform system initialization (system clock config, external memory configuration.. ) */ HAL_PWREx_ClearPendingEvent(); HAL_PWREx_EnterSTOPMode(PWR_MAINREGULATOR_ON, PWR_STOPENTRY_WFE, PWR_D2_DOMAIN); /* Clear HSEM flag */ __HAL_HSEM_CLEAR_FLAG(__HAL_HSEM_SEMID_TO_MASK(HSEM_ID_0)); /* STM32H7xx HAL library initialization: - Systick timer is configured by default as source of time base, but user can eventually implement his proper time base source (a general purpose timer for example or other time source), keeping in mind that Time base duration should be kept 1ms since PPP_TIMEOUT_VALUEs are defined and handled in milliseconds basis. - Set NVIC Group Priority to 4 - Low Level Initialization */ HAL_Init(); /* Infinite loop */ while (1) { } }、

这段代码是一个基于STM32H7xx的单片机系统初始化代码。在该代码中，首先开启了硬件信号量（HSEM）时钟，然后激活了HSEM通知，以便Cortex-M4进入深度睡眠模式等待Cortex-M7进行系统初始化。接着清除了待处理的事件，进入STOP模式并设置为D2域，等待Cortex-M7完成系统初始化。之后，清除了HSEM标志，并初始化了STM32H7xx HAL库，最后进入了一个无限循环。

请解释代码：int main(void) { /HW semaphore Clock enable/ __HAL_RCC_HSEM_CLK_ENABLE(); /* Activate HSEM notification for Cortex-M4*/ HAL_HSEM_ActivateNotification(__HAL_HSEM_SEMID_TO_MASK(HSEM_ID_0)); /* Domain D2 goes to STOP mode (Cortex-M4 in deep-sleep) waiting for Cortex-M7 to perform system initialization (system clock config, external memory configuration.. ) / HAL_PWREx_ClearPendingEvent(); HAL_PWREx_EnterSTOPMode(PWR_MAINREGULATOR_ON, PWR_STOPENTRY_WFE, PWR_D2_DOMAIN); / Clear HSEM flag / __HAL_HSEM_CLEAR_FLAG(__HAL_HSEM_SEMID_TO_MASK(HSEM_ID_0)); / STM32H7xx HAL library initialization: - Systick timer is configured by default as source of time base, but user can eventually implement his proper time base source (a general purpose timer for example or other time source), keeping in mind that Time base duration should be kept 1ms since PPP_TIMEOUT_VALUEs are defined and handled in milliseconds basis. - Set NVIC Group Priority to 4 - Low Level Initialization / HAL_Init(); / Infinite loop */ while (1) { } }

这段代码是一个基本的STM32H7xx单片机的启动代码。下面是代码的详细解释：

1. `__HAL_RCC_HSEM_CLK_ENABLE();` 使能硬件信号量。

2. `HAL_HSEM_ActivateNotification(__HAL_HSEM_SEMID_TO_MASK(HSEM_ID_0));` 激活Cortex-M4的HSEM中断通知，等待Cortex-M7完成系统初始化。

3. `HAL_PWREx_ClearPendingEvent();` 清除电源管理模块的待处理事件。

4. `HAL_PWREx_EnterSTOPMode(PWR_MAINREGULATOR_ON, PWR_STOPENTRY_WFE, PWR_D2_DOMAIN);` 将域D2设置为STOP模式，使Cortex-M4进入深度睡眠状态，等待Cortex-M7完成系统初始化。

5. `__HAL_HSEM_CLEAR_FLAG(__HAL_HSEM_SEMID_TO_MASK(HSEM_ID_0));` 清除HSEM标志。

6. `HAL_Init();` 初始化STM32H7xx HAL库，包括将滴答定时器配置为默认的时间基准源，并将NVIC组优先级设置为4。

7. `while (1) { }` 无限循环，保持单片机处于运行状态。