STM32和GPS的PPS时间同步程序

在STM32和GPS之间进行精确的时间同步需要使用GPS的Pulse Per Second（PPS）信号。下面是一个简单的程序，演示如何使用PPS信号来同步STM32的定时器：

1. 配置USART串口：将GPS的串口连接到STM32的USART外设，并配置USART为接收模式。在接收中断中，读取PPS信号并设置一个标志位。

2. 配置定时器：使用STM32的定时器外设来生成每秒的中断。在每秒中断中，检查标志位是否被设置，并清除标志位。如果标志位已经被设置，则使用定时器的计数器值来更新STM32的系统时钟。

3. 在主循环中反复发送GPS数据，以保持与GPS的连接并更新时间。

下面是一个示例程序，可以帮助你开始编写STM32和GPS的PPS时间同步程序：

#include "stm32f4xx.h"
#include <stdbool.h>

#define GPS_USART USART1
#define PPS_PIN GPIO_Pin_0
#define PPS_PORT GPIOA

volatile bool pps_flag = false;

void init_gps_usart(void) {
    USART_InitTypeDef USART_InitStruct;
    GPIO_InitTypeDef GPIO_InitStruct;
    NVIC_InitTypeDef NVIC_InitStruct;

    RCC_APB2PeriphClockCmd(RCC_APB2Periph_USART1, ENABLE);
    RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOA, ENABLE);

    GPIO_InitStruct.GPIO_Mode = GPIO_Mode_AF;
    GPIO_InitStruct.GPIO_Pin = GPIO_Pin_9 | GPIO_Pin_10;
    GPIO_InitStruct.GPIO_Speed = GPIO_Speed_50MHz;
    GPIO_InitStruct.GPIO_OType = GPIO_OType_PP;
    GPIO_InitStruct.GPIO_PuPd = GPIO_PuPd_UP;
    GPIO_Init(GPIOA, &GPIO_InitStruct);

    GPIO_PinAFConfig(GPIOA, GPIO_PinSource9, GPIO_AF_USART1);
    GPIO_PinAFConfig(GPIOA, GPIO_PinSource10, GPIO_AF_USART1);

    USART_InitStruct.USART_BaudRate = 9600;
    USART_InitStruct.USART_WordLength = USART_WordLength_8b;
    USART_InitStruct.USART_StopBits = USART_StopBits_1;
    USART_InitStruct.USART_Parity = USART_Parity_No;
    USART_InitStruct.USART_HardwareFlowControl = USART_HardwareFlowControl_None;
    USART_InitStruct.USART_Mode = USART_Mode_Rx;
    USART_Init(GPS_USART, &USART_InitStruct);

    USART_ITConfig(GPS_USART, USART_IT_RXNE, ENABLE);

    NVIC_InitStruct.NVIC_IRQChannel = USART1_IRQn;
    NVIC_InitStruct.NVIC_IRQChannelPreemptionPriority = 0;
    NVIC_InitStruct.NVIC_IRQChannelSubPriority = 0;
    NVIC_InitStruct.NVIC_IRQChannelCmd = ENABLE;
    NVIC_Init(&NVIC_InitStruct);

    USART_Cmd(GPS_USART, ENABLE);
}

void init_timer(void) {
    TIM_TimeBaseInitTypeDef TIM_TimeBaseInitStruct;
    NVIC_InitTypeDef NVIC_InitStruct;

    RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM2, ENABLE);

    TIM_TimeBaseInitStruct.TIM_Prescaler = 84 - 1;
    TIM_TimeBaseInitStruct.TIM_CounterMode = TIM_CounterMode_Up;
    TIM_TimeBaseInitStruct.TIM_Period = 1000000 - 1;
    TIM_TimeBaseInitStruct.TIM_ClockDivision = TIM_CKD_DIV1;
    TIM_TimeBaseInitStruct.TIM_RepetitionCounter = 0;
    TIM_TimeBaseInit(TIM2, &TIM_TimeBaseInitStruct);

    NVIC_InitStruct.NVIC_IRQChannel = TIM2_IRQn;
    NVIC_InitStruct.NVIC_IRQChannelPreemptionPriority = 0;
    NVIC_InitStruct.NVIC_IRQChannelSubPriority = 0;
    NVIC_InitStruct.NVIC_IRQChannelCmd = ENABLE;
    NVIC_Init(&NVIC_InitStruct);

    TIM_ITConfig(TIM2, TIM_IT_Update, ENABLE);
    TIM_Cmd(TIM2, ENABLE);
}

void init_pps_pin(void) {
    GPIO_InitTypeDef GPIO_InitStruct;

    RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOA, ENABLE);

    GPIO_InitStruct.GPIO_Mode = GPIO_Mode_IN;
    GPIO_InitStruct.GPIO_Pin = PPS_PIN;
    GPIO_InitStruct.GPIO_PuPd = GPIO_PuPd_UP;
    GPIO_Init(PPS_PORT, &GPIO_InitStruct);
}

void USART1_IRQHandler(void) {
    uint8_t data;

    if (USART_GetITStatus(GPS_USART, USART_IT_RXNE) != RESET) {
        data = USART_ReceiveData(GPS_USART);

        if (data == '$') {
            pps_flag = true;
        }
    }
}

void TIM2_IRQHandler(void) {
    if (TIM_GetITStatus(TIM2, TIM_IT_Update) != RESET) {
        TIM_ClearITPendingBit(TIM2, TIM_IT_Update);

        if (pps_flag) {
            RTC_TimeTypeDef RTC_TimeStruct;
            RTC_DateTypeDef RTC_DateStruct;

            RTC_GetTime(RTC_Format_BIN, &RTC_TimeStruct);
            RTC_GetDate(RTC_Format_BIN, &RTC_DateStruct);

            uint32_t time_in_seconds = RTC_TimeStruct.RTC_Seconds +
                RTC_TimeStruct.RTC_Minutes * 60 +
                RTC_TimeStruct.RTC_Hours * 3600;

            uint32_t timer_value = TIM_GetCounter(TIM2);

            time_in_seconds += timer_value;

            RTC_TimeStruct.RTC_Hours = time_in_seconds / 3600;
            RTC_TimeStruct.RTC_Minutes = (time_in_seconds % 3600) / 60;
            RTC_TimeStruct.RTC_Seconds = time_in_seconds % 60;

            RTC_SetTime(RTC_Format_BIN, &RTC_TimeStruct);

            pps_flag = false;
        }
    }
}

int main(void) {
    init_gps_usart();
    init_timer();
    init_pps_pin();

    while (1) {
        USART_SendData(GPS_USART, 'G');
        USART_SendData(GPS_USART, 'P');
        USART_SendData(GPS_USART, 'S');
        USART_SendData(GPS_USART, '\r');
        USART_SendData(GPS_USART, '\n');

        delay(1000);
    }
}

注意：这只是一个简单的示例程序，需要根据你的具体需求进行修改和完善。