我需要stm32开发板来写一个程序，达到通过串口向上位机发送数据，数据内容为时间，格式按x:xxcxx显示，时间数据应为实时变化数据。串口功能通过KEYo控制，当KEYo按下时串口开始发送，当再次按下时串口停止发送的效果，代码是怎么样的

您可以参考以下代码实现您的需求：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "stm32f10x.h"

#define USART1_RX_GPIO GPIOA
#define USART1_RX_PIN GPIO_Pin_10

#define USART1_TX_GPIO GPIOA
#define USART1_TX_PIN GPIO_Pin_9

#define USART1 GPIOA
#define USART1_CLK RCC_APB2Periph_USART1
#define USART1_BAUDRATE 115200

#define LED_GPIO GPIOB
#define LED_PIN GPIO_Pin_1

#define KEY_GPIO GPIOC
#define KEY_PIN GPIO_Pin_13

USART_InitTypeDef USART_InitStructure;

void USART1_Config(void)
{
    GPIO_InitTypeDef GPIO_InitStructure;

    RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA | RCC_APB2Periph_GPIOB | RCC_APB2Periph_GPIOC | RCC_APB2Periph_AFIO, ENABLE);

    /* Configure USART1 Rx (PA10) as input floating */
    GPIO_InitStructure.GPIO_Pin = USART1_RX_PIN;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IN_FLOATING;
    GPIO_Init(USART1_RX_GPIO, &GPIO_InitStructure);

    /* Configure USART1 Tx (PA9) as alternate function push-pull */
    GPIO_InitStructure.GPIO_Pin = USART1_TX_PIN;
    GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP;
    GPIO_Init(USART1_TX_GPIO, &GPIO_InitStructure);

    /* Configure KEY0 (PC13) as input pull-up */
    GPIO_InitStructure.GPIO_Pin = KEY_PIN;
    GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IPU;
    GPIO_Init(KEY_GPIO, &GPIO_InitStructure);

    /* Configure LED (PB1) as output push-pull */
    GPIO_InitStructure.GPIO_Pin = LED_PIN;
    GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_Out_PP;
    GPIO_Init(LED_GPIO, &GPIO_InitStructure);

    /* Configure USART1 */
    USART_InitStructure.USART_BaudRate = USART1_BAUDRATE;
    USART_InitStructure.USART_WordLength = USART_WordLength_8b;
    USART_InitStructure.USART_StopBits = USART_StopBits_1;
    USART_InitStructure.USART_Parity = USART_Parity_No;
    USART_InitStructure.USART_HardwareFlowControl = USART_HardwareFlowControl_None;
    USART_InitStructure.USART_Mode = USART_Mode_Tx;
    USART_Init(USART1, &USART_InitStructure);

    USART_Cmd(USART1, ENABLE);
}

void USART1_Send(const char *data)
{
    while (*data != '\0') {
        USART_SendData(USART1, *data++);
        while (USART_GetFlagStatus(USART1, USART_FLAG_TXE) == RESET);
    }
}

char* int2str(int num, int radix)
{
    static char str[16];
    int i = 0;

    do {
        int t = num % radix;
        str[i++] = t > 9 ? t - 10 + 'a' : t + '0';
    } while (num /= radix);

    str[i] = '\0';

    for (int j = 0; j < i / 2; j++) {
        char t = str[j];
        str[j] = str[i - j - 1];
        str[i - j - 1] = t;
    }

    return str;
}

void SysTick_Handler(void)
{
    static int count = 0;
    static int send = 0;

    if (++count == 1000) {
        count = 0;
        char *hour = int2str(RTC_GetCounter(RTC) / 3600 % 24, 10);
        char *minute = int2str(RTC_GetCounter(RTC) / 60 % 60, 10);
        char *second = int2str(RTC_GetCounter(RTC) % 60, 10);
        char *data = malloc(strlen(hour) + 2 + strlen(minute) + 2 + strlen(second) + 1);

        sprintf(data, "%s:%s:%s", hour, minute, second);

        if (send) {
            USART1_Send(data);
            USART1_Send("\r\n");
        }

        free(data);
    }
}

int main(void)
{
    SystemInit();

    /* Configure SysTick */
    SysTick_Config(SystemCoreClock / 1000);

    /* Configure RTC */
    RCC_APB1PeriphClockCmd(RCC_APB1Periph_PWR, ENABLE);
    PWR_BackupAccessCmd(ENABLE);
    RCC_LSEConfig(RCC_LSE_ON);
    while (RCC_GetFlagStatus(RCC_FLAG_LSERDY) == RESET);
    RCC_RTCCLKConfig(RCC_RTCCLKSource_LSE);
    RCC_RTCCLKCmd(ENABLE);
    RTC_WaitForSynchro();
    RTC_InitStructure.RTC_AsynchPrediv = 127;
    RTC_InitStructure.RTC_SynchPrediv = 249;
    RTC_InitStructure.RTC_HourFormat = RTC_HourFormat_24;
    RTC_Init(&RTC_InitStructure);
    RTC_SetCounter(0x00000000);
    RTC_WaitForLastTask();

    USART1_Config();

    while (1) {
        if (GPIO_ReadInputDataBit(KEY_GPIO, KEY_PIN) == RESET) {
            send = !send;

            if (send) {
                GPIO_SetBits(LED_GPIO, LED_PIN);
                USART1_Send("UART start!\r\n");
            } else {
                GPIO_ResetBits(LED_GPIO, LED_PIN);
                USART1_Send("UART stop!\r\n");
            }

            /* Wait for key release */
            while (GPIO_ReadInputDataBit(KEY_GPIO, KEY_PIN) == RESET);
        }
    }
}

这是一个基于STM32的程序，通过串口向上位机发送实时时间数据。其中 KEY0（PC13）控制串口发送任务的启停，当按下KEY0时，LED（PB1）闪烁表示串口开始发送任务，再次按下KEY0时，LED停止闪烁，表示串口停止发送任务。串口发送的时间数据格式为x:xxcxx。