当检测到距离小于 1m 的物体时，我试图通过简单地打开 LED 来控制这个 HC-SR4 超声波传感器。我使用 TIM2 作为触发信号（引脚 PB10），使用 TIM4 接收回波信号（引脚 PB6）。LED 连接到引脚 PB7。当我加载下面的代码时，LED 只是打开，不管有没有物体，它只是打开。
知道我哪里出错了吗？
#include <stdio.h>
#include "stm32l1xx.h" // Keil::Device:Startup
// switch from HSE to HSI clock 16MHz
void HSI_config(){
RCC->CR |= RCC_CR_HSION; // Turn On HSI oscillator
RCC->CFGR |= RCC_CFGR_SW; // Select HSI clock
RCC->CFGR |= RCC_CFGR_SWS_HSI;
RCC->CR |= RCC_CR_HSIRDY; // wait for HSI stabilize
}
// Configure GPIO Port B
void GPIO_config(){
RCC->AHBRSTR |= RCC_AHBRSTR_GPIOBRST; // Reset GPIOB clock
RCC->AHBRSTR &= ~RCC_AHBRSTR_GPIOBRST; // Clear Reset
RCC->AHBENR |= RCC_AHBENR_GPIOBEN; // Enable GPIOB clock
//PB6 Echo Pin
GPIOB->MODER &= ~(0x03 << (2*6)); // Clear bit 12 & 13 Alternate function mode
GPIOB->MODER |= 0x02 << (2*6); // set as Alternate function mode
GPIOB->OSPEEDR &= ~(0x03<< (2*6)); // 40 MHz speed
GPIOB->OSPEEDR |= 0x03<< (2*6); // 40 MHz speed
GPIOB->PUPDR &= ~(1<<6); // NO PULL-UP PULL-DOWN
GPIOB->OTYPER &= ~(1<<6); // PUSH-PULL
GPIOB->AFR[0] |= 0x2 << (4*6); // set PB pin 6 as AF2 (TIM4_CH1)
//PB10 Pluse Generating Pin
GPIOB->MODER &= ~(0x03 << (2*10)); // Clear bit 12 & 13 Alternate function mode
GPIOB->MODER |= 0x02 << (2*10); // set as Alternate function mode
GPIOB->OSPEEDR &= ~(0x03<< (2*10)); // 40 MHz speed
GPIOB->OSPEEDR |= 0x03<< (2*10); // 40 MHz speed
GPIOB->PUPDR &= ~(1<<10); // NO PULL-UP PULL-DOWN
GPIOB->OTYPER &= ~(1<<10); // PUSH-PULL
GPIOB->AFR[1] |= 0x1 << (4*2); // set PB pin 10 as AF1 (TIM2_CH3)
//PB7 LED ON/OFF
GPIOB->MODER |= GPIO_MODER_MODER7_0; // General purpose output mode
GPIOB->OSPEEDR |= GPIO_OSPEEDER_OSPEEDR7; // Max High speed 50MHz
}
// CONFIGURE TIM4 FOR RECEIVING INPUT SIGNAL
void TIM4_Enable(){
RCC->APB1ENR |= RCC_APB1ENR_TIM4EN; // ENABLE TIM4 CLOCK
TIM4->PSC = 15; // SET APPROPRAIT PRESCALER TO SLOW DOWN THE CLOCK
TIM4->ARR = 0XFFFF; // SET MAX PULSE WIDTH OF 65536us FOR 16-BIT TIMER
TIM4->CCMR1 &= ~TIM_CCMR1_CC1S; // CLEAR CAPTURE/COMPARE REGISTER
TIM4->CCMR1 |= 0X1; // SELECT CH1 INPUTE CAPTURE
TIM4->CCMR1 &= ~TIM_CCMR1_IC1F; // DISABLE DIGITAL FILTERING
TIM4->CCER |= (1<<1 | 1<<3); // SELECT BOTH RISING AND FALLING EDGE DETECTION CC1P & CC1NP
TIM4->CCMR1 &= ~(TIM_CCMR1_IC1PSC); // INPUT PRESCALER 0 TO CAPTURE EACH VALID EDGE
TIM4->CCER |= TIM_CCER_CC1E; // ENABLE COUNTER CAPTURE
TIM4->DIER |= TIM_DIER_CC1IE; // ENABLE CH1 CAPTURE/COMPARE INTERRUPT
NVIC_SetPriority(TIM4_IRQn, 1); // SET PRIORITY TO 1
NVIC_EnableIRQ(TIM4_IRQn); //ENABLE TIM4 INTERRUPT IN NVIC
}
// CONFIGURE TIM2 FOR SENDING OUTPUT SIGNAL
void TIM2_Enable(){
RCC->APB1ENR |= RCC_APB1ENR_TIM2EN; // ENABLE TIM2 CLOCK
TIM2->PSC = 15; // SET APPROPRAIT PRESCALER TO SLOW DOWN THE CLOCK
TIM2->ARR = 0XFFFF; // SET MAX PULSE WIDTH OF 65536us FOR 16-BIT TIMER
TIM2->CCMR2 |= TIM_CCMR2_OC3M_1 | TIM_CCMR2_OC3M_2; // 111: PWM mode 1
TIM2->CCMR2 |= TIM_CCMR2_OC3PE; // CH3 Output Preload Enable
TIM2->CR1 |= TIM_CR1_ARPE; // Auto-reload Prelaod Enable
TIM2->CCER |= TIM_CCER_CC3E; // Enable Output for CH3
TIM2->EGR |= TIM_EGR_UG; // Force Update
TIM2->SR &= ~TIM_SR_UIF; // Clear the Update Flag
TIM2->DIER |= TIM_DIER_UIE; // Enable Interrupt on Update
TIM2->CR1 |= TIM_CR1_DIR; // Set downcounting counter direction
TIM2->CR1 |= TIM_CR1_CEN; // Enable Counter
}
//Initialize the float variables.
volatile uint8_t timespan = 0; // Total pulse width
volatile uint8_t lastcounter = 0; // Timer counter value of the last event
volatile uint8_t newcounter = 0; // Timer counter value of the current event
volatile uint8_t overflow = 0; // Count the number of overflows
volatile uint8_t PulseEnd = 0; // Declare end of pulse
void Echo_TIM4_IRQHandler(){
if ((TIM4->SR & TIM_SR_UIF) != 0){ // Check the update even flag
overflow = overflow + 1; // if UIF = 1, increment overflow counter
TIM4->SR &= ~TIM_SR_UIF; // clear UIF
}
if ((TIM4->SR & TIM_SR_CC1IF) != 0){ // Check capture event flag
newcounter = TIM4->CCR1; // read capture value, store as newcounter
timespan = (newcounter - lastcounter)+(65536 * overflow); // calculate the total pulse width
lastcounter = newcounter; // save the value of newcounter as lastcounter to be used for the next cycle
overflow = 0; // clear overflow counter
PulseEnd = 1;
}
}
void setSysTick(void){
// ---------- SysTick timer (1ms) -------- //
if (SysTick_Config(SystemCoreClock / 1000)) {
// Capture error
while (1){};
}
}
volatile uint32_t msTicks; //counts 1ms timeTicks
void SysTick_Handler(void) {
msTicks++;
}
static void Delay(__IO uint32_t dlyTicks){
uint32_t curTicks = msTicks;
while ((msTicks - curTicks) < dlyTicks);
}
int main(void){
float Distance = 0.0f; // actual distance in cm
int Pulsesent = 0;
HSI_config();
setSysTick();
GPIO_config();
TIM4_Enable();
Echo_TIM4_IRQHandler();
while(1){
if (Pulsesent == 0) {
(Pulsesent = 1);
TIM2_Enable();
}
if(Pulsesent && PulseEnd){
Pulsesent = 0;
if(overflow == 1){
timespan = 0;
}
else {
Distance = (timespan / 58) ;
}
Delay(1);
}
if (Distance <= 100){
GPIOB->BSRRL = (1<<7);
}
else {
GPIOB->BSRRL = (0<<7);
}
}
}