问题2：释义以下程序含义，结果demo程序。 #include "key.h" void key_init(void) { /* 按键1接口初始化 */ KEY1_GPIO_PCLK_TREE |= 0X1 << KEY1_GPIO_PCLK_TREE_BIT; KEY1_GPIO_PORT->MODER &= ~(0X3 << KEY1_GPIO_PIN * 2); KEY1_GPIO_PORT->PUPDR &= ~(0X3 << KEY1_GPIO_PIN * 2); /* 按键2接口初始化 */ KEY2_GPIO_PCLK_TREE |= 0X1 << KEY2_GPIO_PCLK_TREE_BIT; KEY2_GPIO_PORT->MODER &= ~(0X3 << KEY2_GPIO_PIN * 2); KEY2_GPIO_PORT->PUPDR &= ~(0X3 << KEY2_GPIO_PIN * 2); /* 按键3接口初始化 */ KEY3_GPIO_PCLK_TREE |= 0X1 << KEY3_GPIO_PCLK_TREE_BIT; KEY3_GPIO_PORT->MODER &= ~(0X3 << KEY3_GPIO_PIN * 2); KEY3_GPIO_PORT->PUPDR &= ~(0X3 << KEY3_GPIO_PIN * 2); } static void key_delay(void) { uint32_t delay_count = 5000 * KEY_SOFT_TIME_VALUE; for(uint32_t i = 0; i < delay_count; i++) { ; } } uint8_t key_scan(void) { static uint8_t key_status = 0; if((KEY1_SCAN == 1 || KEY2_SCAN == 0 || KEY3_SCAN == 0) && key_status == 0) { key_delay(); if(KEY1_SCAN == 1) { key_status = 1; return KEY_ONE; } if(KEY2_SCAN == 0) { key_status = 1; return KEY_TWO; } if(KEY3_SCAN == 0) { key_status = 1; return KEY_THREE; } } else if(KEY1_SCAN == 0 && KEY2_SCAN == 1 && KEY3_SCAN == 1) { key_status = 0; } return KEY_ERR; }