基于stm32的四路抢答器代码设计，要求：1.设置四路抢答器，1路为主持人线路；2.主持人按下开始按键后，选手抢答；3.第一位选手抢答成功后，其余选手抢答无效；4.抢答结束后，主持人按下按键系统复位

下面是一份基于STM32的四路抢答器的代码设计，代码中使用了外部中断、定时器和GPIO等模块来实现该功能。请注意，这份代码只是一个参考，具体实现还需根据实际情况进行调整。

#include "stm32f10x.h"

#define KEY1_PIN GPIO_Pin_0
#define KEY2_PIN GPIO_Pin_1
#define KEY3_PIN GPIO_Pin_2
#define KEY4_PIN GPIO_Pin_3
#define KEY1_PORT GPIOA
#define KEY2_PORT GPIOA
#define KEY3_PORT GPIOA
#define KEY4_PORT GPIOA
#define KEY1_EXTI_LINE EXTI_Line0
#define KEY2_EXTI_LINE EXTI_Line1
#define KEY3_EXTI_LINE EXTI_Line2
#define KEY4_EXTI_LINE EXTI_Line3
#define KEY1_NVIC_IRQChannel EXTI0_IRQn
#define KEY2_NVIC_IRQChannel EXTI1_IRQn
#define KEY3_NVIC_IRQChannel EXTI2_IRQn
#define KEY4_NVIC_IRQChannel EXTI3_IRQn

#define TIMER_PERIOD 1000 // 定时器周期为1ms
#define RESET_TIME 5000 // 每轮抢答结束后的复位时间为5s

uint8_t is_answered = 0; // 是否已有选手抢答成功
uint8_t reset_countdown = 0; // 倒计时复位计数器

void TIM2_IRQHandler(void) {
    if (TIM_GetITStatus(TIM2, TIM_IT_Update) != RESET) {
        if (reset_countdown > 0) {
            reset_countdown--;
        }
        TIM_ClearITPendingBit(TIM2, TIM_IT_Update);
    }
}

void EXTI0_IRQHandler(void) {
    if (EXTI_GetITStatus(KEY1_EXTI_LINE) != RESET) {
        if (!is_answered) {
            is_answered = 1;
            // 选手1抢答成功
        }
        EXTI_ClearITPendingBit(KEY1_EXTI_LINE);
    }
}

void EXTI1_IRQHandler(void) {
    if (EXTI_GetITStatus(KEY2_EXTI_LINE) != RESET) {
        if (!is_answered) {
            is_answered = 1;
            // 选手2抢答成功
        }
        EXTI_ClearITPendingBit(KEY2_EXTI_LINE);
    }
}

void EXTI2_IRQHandler(void) {
    if (EXTI_GetITStatus(KEY3_EXTI_LINE) != RESET) {
        if (!is_answered) {
            is_answered = 1;
            // 选手3抢答成功
        }
        EXTI_ClearITPendingBit(KEY3_EXTI_LINE);
    }
}

void EXTI3_IRQHandler(void) {
    if (EXTI_GetITStatus(KEY4_EXTI_LINE) != RESET) {
        if (!is_answered) {
            is_answered = 1;
            // 选手4抢答成功
        }
        EXTI_ClearITPendingBit(KEY4_EXTI_LINE);
    }
}

int main(void) {
    GPIO_InitTypeDef GPIO_InitStructure;
    NVIC_InitTypeDef NVIC_InitStructure;
    EXTI_InitTypeDef EXTI_InitStructure;
    TIM_TimeBaseInitTypeDef TIM_TimeBaseStructure;

    RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA, ENABLE); // 使能GPIOA时钟
    RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM2, ENABLE); // 使能TIM2时钟

    // 配置按键引脚为输入
    GPIO_InitStructure.GPIO_Pin = KEY1_PIN | KEY2_PIN | KEY3_PIN | KEY4_PIN;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IPU;
    GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
    GPIO_Init(KEY1_PORT, &GPIO_InitStructure);
    GPIO_Init(KEY2_PORT, &GPIO_InitStructure);
    GPIO_Init(KEY3_PORT, &GPIO_InitStructure);
    GPIO_Init(KEY4_PORT, &GPIO_InitStructure);

    // 配置按键引脚为外部中断
    EXTI_InitStructure.EXTI_Line = KEY1_EXTI_LINE | KEY2_EXTI_LINE | KEY3_EXTI_LINE | KEY4_EXTI_LINE;
    EXTI_InitStructure.EXTI_Mode = EXTI_Mode_Interrupt;
    EXTI_InitStructure.EXTI_Trigger = EXTI_Trigger_Falling;
    EXTI_InitStructure.EXTI_LineCmd = ENABLE;
    EXTI_Init(&EXTI_InitStructure);

    // 配置按键引脚对应的中断向量
    NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0x01;
    NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0x01;
    NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
    NVIC_InitStructure.NVIC_IRQChannel = KEY1_NVIC_IRQChannel;
    NVIC_Init(&NVIC_InitStructure);
    NVIC_InitStructure.NVIC_IRQChannel = KEY2_NVIC_IRQChannel;
    NVIC_Init(&NVIC_InitStructure);
    NVIC_InitStructure.NVIC_IRQChannel = KEY3_NVIC_IRQChannel;
    NVIC_Init(&NVIC_InitStructure);
    NVIC_InitStructure.NVIC_IRQChannel = KEY4_NVIC_IRQChannel;
    NVIC_Init(&NVIC_InitStructure);

    // 配置定时器2
    TIM_TimeBaseStructure.TIM_Period = TIMER_PERIOD - 1;
    TIM_TimeBaseStructure.TIM_Prescaler = 7199; // 计数频率为1MHz
    TIM_TimeBaseStructure.TIM_ClockDivision = TIM_CKD_DIV1;
    TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;
    TIM_TimeBaseInit(TIM2, &TIM_TimeBaseStructure);
    TIM_Cmd(TIM2, ENABLE);
    TIM_ITConfig(TIM2, TIM_IT_Update, ENABLE);

    while (1) {
        if (reset_countdown == 0 && is_answered) {
            // 每轮抢答结束后的复位
            is_answered = 0;
            reset_countdown = RESET_TIME / TIMER_PERIOD;
            // 复位操作
        }
    }
}