C 在 if/else 语句中执行内容的频率/时间？

Question

我正在做一个嵌入式 (avr) 项目，基本上我想根据一个大头针被按下的时间打印出一些不同的东西。我无法弄清楚当值通过时会发生什么并满足沿途的 if 语句（按钮仍被按下，因此计数器递增）。

设置如下：

如果溢出在 7-48 之间（按钮按下 30ms-200ms），打印出一个 '.'
如果溢出大于 48（按钮按下超过 200 毫秒），打印出一个 '-'
如果溢出大于 97（超过 400 毫秒没有按下按钮），打印出一个 ' '

我目前的代码如下：

static inline void isr(char type) {
static unsigned int overflows = 0;
static unsigned char idx = 0;
if (type == 'e') { // edge captured
    if (TCCR1B & 0x40) { // rising edge
        if (overflows < 7) {
            // do nothing
        } else if (overflows < 49) {
            buffer[idx++] = '.';
            size++;
        } else {
            buffer[idx++] = '-';
            size++;
        }
    }
    overflows = 0; // restart counting overflows at each edge
} else { // overflow occured
    overflows++;
    if (buffer[idx-1] != ' ' && !(TCCR1B & 0x40) && overflows > 97) {
        buffer[idx++] = ' ';
        size++;
    }
}

我不确定这是否正确，因为似乎在“-”之前总会有一个“.”，因为随着溢出值的增加，它满足

有什么想法吗？

Answer 1

如果你想计算按下开关的次数，你可以使用 while 循环。 例如，

    if(sw==0) //sw is switch connected with I/O pin
    {
      while(sw==0)
      {
       led=1; //LED is output
       delay(); // use delay function
       led=0;
       delay();
       count++;
       }
     }

通过使用 while 循环，您可以避免多次按下开关。如果你做一个开关，计数会加一。

Answer 2

我不确定这是否正确，因为似乎总会有一个“。”在'-'之前，因为作为溢出 值递增，满足

但测试仅在上升沿执行 - 当 type == 'e' 和 (TCCR1B & 0x40) != 0 时。因此，overflow 计数仅在释放按钮时计算，因此您不会在- 之前看到中间的.。

因此，为了回答您的问题，条件为真时执行条件语句或块。这里有嵌套条件，因此所有前面的条件都必须为真才能评估内部条件。

Answer 3

根据您的描述，我假设您的引脚上有一个按钮，因此在这种情况下，我建议在做任何事情之前首先为按钮信号实现去抖动。 我会像这样解决问题：

#define BUTTON_UNKNOWN  0
#define BUTTON_DOWN     1
#define BUTTON_UP       2

#define FALSE           0
#define TRUE            1

static inline unsigned char debounce( unsigned char current_state)
{
static unsigned char ret_value;
unsigned char state_changed = FALSE;
// Counter for number of equal states
static unsigned char count = 0;
// Keeps track of current (de-bounced) state
static unsigned char button_state = 0;
// Check if button is high or low for the moment
if (current_state != button_state) 
{
    // Button state is about to be changed, increase counter
    count++;
    if (count >= 3) 
        {
        // The button have not bounced for four checks, change state
        button_state = current_state;
        // If the button was pressed (not released), tell main so
        count = 0;
        state_changed = TRUE;
        }
} 
else 
{
state_changed = FALSE;
// Reset counter
count = 0;
}

//if butten press or release detected
if (state_changed == TRUE)
{
    //check for the current state of the button
    if (current_state != 0) 
        {
        ret_value = BUTTON_DOWN;
        }
    else
        {
        ret_value = BUTTON_UP;
        }
}

return ret_value;
}

int main(void)
{
//perform proper initialization of your pin

unsigned char button = BUTTON_UNKNOWN;    
unsigned char cycle_count  = 0;
unsigned char idx = 0;
unsigned char buffer[255];
unsigned char current_state;
unsigned char no_activity;
//unsigned char current_state = (~BUTTON_PIN & BUTTON_MASK) != 0;

while(1)
{
//read the button state
current_state = (~BUTTON_PIN & BUTTON_MASK) != 0;
// Update button_state
button = debounce(current_state);
// Check if the button is pressed.
if (button == BUTTON_DOWN)
{
    //count cycles in which the button was pressed
    //one cycle is 10 ms - see delay below
    cycle_count++;
}
else
{
    //check if the button was pressed before
    if ((button != BUTTON_UNKNOWN) && (cycle_count != 0))
    {
        //if button was pressed for 200ms
        if (cycle_count <= 20)
        {
            buffer[idx] = '.';
            idx++;            
        }
        else
        {
            //if the button was pressed between 200 and 400 ms
            if ((cycle_count > 20) && (cycle_count <= 40))
            {
               buffer[idx] = '-';
               idx++;
            }
            //the button was pressed for more than 400ms, uncomment if you need it

            /*else
            {
               buffer[idx] = ' ';
               idx++;
            }*/

        }
        //reset counting mechanism
        cycle_count = 0;
        no_activity = 0; 
    }
    else
    {
        no_activity++;
        if (no_activity >= 40)
        {
            buffer[idx] = ' ';
            idx++;
            no_activity = 0;
        }
    }
}

// Delay for a while so we don’t check to button too often
_delay_ms(10);
}
}

您可以根据需要调整此代码： 更改行 current_state = (~BUTTON_PIN & BUTTON_MASK) != 0; 以便读取您的引脚状态，并更改缓冲区的声明以满足您的需要 unsigned char buffer[255];

请注意，由于去抖，测得的时间不完全是 200ms（它是 200ms + 2*debounce_time = 260ms（去抖时间是 3 个周期，每个周期是 10ms，见最后的延迟），但你可以补偿最后通过减少 cycle_count 比较中的内容来解决这些错误。

希望这会有所帮助！

如果你真的坚持你的解决方案，那么为了避免你遇到的问题是不要连续评估溢出值，不要试图确定按钮按下的长度，而是尝试测量长度推，然后评估它并将字符放入缓冲区。您需要等待“释放按钮”，然后评估按下按钮的时间。像这样的：

static inline void isr(char type) {
static unsigned int overflows = 0;
static unsigned char idx = 0;
unsiged char button_status;

if (type == 'e') { // edge captured
    if (TCCR1B & 0x40) { // rising edge
        //perform a debounce otherwise wont be good
        button_status = 1;

    }
    overflows = 0; // restart counting overflows at each edge
} else { // overflow occured  
    overflows++;
     //if button was pressed and its now released evaluate result
    if (!(TCCR1B & 0x40) && (button_status == 1))
    {
        if (overflows < 7) {
            // do nothing
        } else if (overflows < 49) {
            buffer[idx++] = '.';
            size++;
        } else {
            buffer[idx++] = '-';
            size++;
        }
        button_status = 0;
    }
    if (buffer[idx-1] != ' ' && !(TCCR1B & 0x40) && overflows > 97) {
        buffer[idx++] = ' ';
        size++;
    }
}