iic总线的Wire.onRequest(requestEvent)函数问题

jinpenghf

看过网上一些主从机iic总线的程序，后自改写发现Wire.onRequest(requestEvent);这个函数如果初始化两个程序的话，如

Serial.begin(9600);      
  Wire.begin(2);   
  Wire.onReceive(pair);
  Wire.onRequest(pair);
  Wire.onReceive(receiveEvent);
  Wire.onRequest(requestEvent);
  最终执行的是  Wire.onRequest(requestEvent); 这个函数，上一个函数并未执行，另外
子函数
void pair(int a)
{
  char c = Wire.read();
    Serial.print(c);  
    Wire.onRequest(pair);
}
是无法调用Wire.onRequest(pair)函数，求大神指教

Super169

這是很正常, onRequest 是設定有 request 時要執行的函數, 你再設定一次, 就把原先的改了.

比如以下例子:

1. int a;
   
2. 
   
3. a = 1;
   
4. a = 2;

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你會因為最後 a 的值變成 2 而覺得有問題嗎?

jinpenghf

Super169 发表于 2015-3-24 17:23
這是很正常, onRequest 是設定有 request 時要執行的函數, 你再設定一次, 就把原先的改了.

比如以下例子 ...

哦，也就是说要接受多个数据，是在事件子函数requestEvent里面改，一个程序里面只能有一个Wire.onReceive(receiveEvent);  Wire.onRequest(requestEvent); 还有这个函数是不是不能被其他函数调用

Super169

你看看 Wire.onReceive 及 Wire.onRequest 的源碼, 就會明白了, 只是一句簡單的 設定.

1. // sets function called on slave write
   
2. void TwoWire::onReceive( void (*function)(int) )
   
3. {
   
4.   user_onReceive = function;
   
5. }
   
6. 
   
7. // sets function called on slave read
   
8. void TwoWire::onRequest( void (*function)(void) )
   
9. {
   
10.   user_onRequest = function;
    
11. }
    

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情況就等同於執行  a = 1; 一樣.

Super169

之後, 當有需要時, 就是這樣執行你設定的 function:

1. // behind the scenes function that is called when data is received
   
2. void TwoWire::onReceiveService(uint8_t* inBytes, int numBytes)
   
3. {
   
4.   // don't bother if user hasn't registered a callback
   
5.   if(!user_onReceive){
   
6.     return;
   
7.   }
   
8.   // don't bother if rx buffer is in use by a master requestFrom() op
   
9.   // i know this drops data, but it allows for slight stupidity
   
10.   // meaning, they may not have read all the master requestFrom() data yet
    
11.   if(rxBufferIndex < rxBufferLength){
    
12.     return;
    
13.   }
    
14.   // copy twi rx buffer into local read buffer
    
15.   // this enables new reads to happen in parallel
    
16.   for(uint8_t i = 0; i < numBytes; ++i){
    
17.     rxBuffer[i] = inBytes[i];   
    
18.   }
    
19.   // set rx iterator vars
    
20.   rxBufferIndex = 0;
    
21.   rxBufferLength = numBytes;
    
22.   // alert user program
    
23.   user_onReceive(numBytes);
    
24. }
    
25. 
    
26. // behind the scenes function that is called when data is requested
    
27. void TwoWire::onRequestService(void)
    
28. {
    
29.   // don't bother if user hasn't registered a callback
    
30.   if(!user_onRequest){
    
31.     return;
    
32.   }
    
33.   // reset tx buffer iterator vars
    
34.   // !!! this will kill any pending pre-master sendTo() activity
    
35.   txBufferIndex = 0;
    
36.   txBufferLength = 0;
    
37.   // alert user program
    
38.   user_onRequest();
    
39. }
    

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jinpenghf

哦哦，就直接改里面的值了，但他是一个函数应该可以被调用啊，我却调用不了

jinpenghf

Super169 发表于 2015-3-24 17:43
之後, 當有需要時, 就是這樣執行你設定的 function:

// behind the scenes function that is called whe ...

谢谢了啊，查看了库基本明白了