pulseIn函数工作，PC指针是不是一直在函数内部

zhixiang

pulseIn函数工作时，PC指针是不是一直在函数内部，直到电平变化为止，然后跳出函数，运行一个指针命令。，比如高电平持续了3s,那这3s指针一直停留在这里计数，其他的事都坐不了？Arduino不好单步调试，请知道的朋友指点迷津，谢谢

pathletboy

最好的解释就是直接看代码。

1. /* Measures the length (in microseconds) of a pulse on the pin; state is HIGH
   
2. * or LOW, the type of pulse to measure.  Works on pulses from 2-3 microseconds
   
3. * to 3 minutes in length, but must be called at least a few dozen microseconds
   
4. * before the start of the pulse. */
   
5. unsigned long pulseIn(uint8_t pin, uint8_t state, unsigned long timeout)
   
6. {
   
7.         // cache the port and bit of the pin in order to speed up the
   
8.         // pulse width measuring loop and achieve finer resolution.  calling
   
9.         // digitalRead() instead yields much coarser resolution.
   
10.         uint8_t bit = digitalPinToBitMask(pin);
    
11.         uint8_t port = digitalPinToPort(pin);
    
12.         uint8_t stateMask = (state ? bit : 0);
    
13.         unsigned long width = 0; // keep initialization out of time critical area
    
14.        
    
15.         // convert the timeout from microseconds to a number of times through
    
16.         // the initial loop; it takes 16 clock cycles per iteration.
    
17.         unsigned long numloops = 0;
    
18.         unsigned long maxloops = microsecondsToClockCycles(timeout) / 16;
    
19.        
    
20.         // wait for any previous pulse to end
    
21.         while ((*portInputRegister(port) & bit) == stateMask)
    
22.                 if (numloops++ == maxloops)
    
23.                         return 0;
    
24.        
    
25.         // wait for the pulse to start
    
26.         while ((*portInputRegister(port) & bit) != stateMask)
    
27.                 if (numloops++ == maxloops)
    
28.                         return 0;
    
29.        
    
30.         // wait for the pulse to stop
    
31.         while ((*portInputRegister(port) & bit) == stateMask) {
    
32.                 if (numloops++ == maxloops)
    
33.                         return 0;
    
34.                 width++;
    
35.         }
    
36. 
    
37.         // convert the reading to microseconds. The loop has been determined
    
38.         // to be 20 clock cycles long and have about 16 clocks between the edge
    
39.         // and the start of the loop. There will be some error introduced by
    
40.         // the interrupt handlers.
    
41.         return clockCyclesToMicroseconds(width * 21 + 16);
    
42. }

复制代码

zhixiang

pathletboy 发表于 2014-7-26 10:07
最好的解释就是直接看代码。/* Measures the length (in microseconds) of a pulse on the pin; state is H ...

谢谢你的回复。但是光看这段代码，看不出pulseIn函数的工作模式，在板子上测试，得出运行时，PC指针没有在pulseIn内部停留，包括Mode相符时，计算出的脉冲时间也有一段延时。总体来着，用起来不是很方便。不知道大家用起来怎么样，有什么心得