I2C ReSTART returns Success (#2141)

* Don't Return I2C_ERROR_CONTINUE on ReSTART

ReSTART operations on the ESP32 have to be handled differently than on AVR chips, so ReSTART operations(`Wire.endTransmission(false), Wire.requestFrom(id,size,false);` are queued until a STOP is send (`Wire.endTransmission(TRUE), Wire.endTransmission(), Wire.requestFrom(id,size), Wire.requestFrom(id,size,TRUE)). To indicate the queuing I had used `I2C_ERROR_CONTINUE`, this caused compatibility issues with the existing Arduino I2C Code base. So, back to Lying to the public(for their own good of course) about success!  This update just returns `I2C_ERROR_OK` on ReSTART commands.

* add comments

add comments

* Change Return error for ReSTART operation to I2C_ERROR_OK

This change restores compatibility with pre-existing Arduino Libraries.  The ReSTART queuing operations are hidden behind the scenes.  Wire.endTransmission(id,len,FALSE); will know return I2C_ERROR_OK instead of I2C_ERROR_CONTINUE, Wire.lastError() will return the true condition of I2C_ERROR_CONTINUE.

libraries/Wire/src/Wire.cpp

@@ -154,14 +154,15 @@ void TwoWire::beginTransmission(uint16_t address)
 uint8_t TwoWire::endTransmission(bool sendStop)  // Assumes Wire.beginTransaction(), Wire.write()
 {
     if(transmitting == 1) {
+            // txlength is howmany bytes in txbuffer have been use
         last_error = writeTransmission(txAddress, &txBuffer[txQueued], txLength - txQueued, sendStop);
-        rxIndex = 0;
-        rxLength = rxQueued;
-        rxQueued = 0;
-        txQueued = 0; // the SendStop=true will restart all Queueing
         if(last_error == I2C_ERROR_CONTINUE){
-            // txlength is howmany bytes in txbuffer have been use
             txQueued = txLength;
+        } else if( last_error == I2C_ERROR_OK){
+          rxIndex = 0;
+          rxLength = rxQueued;
+          rxQueued = 0;
+          txQueued = 0; // the SendStop=true will restart all Queueing
         }
     } else {
         last_error = I2C_ERROR_NO_BEGIN;
@@ -170,7 +171,7 @@ uint8_t TwoWire::endTransmission(bool sendStop)  // Assumes Wire.beginTransactio
     txIndex = 0;
     txLength = 0;
     transmitting = 0;
-    return last_error;
+    return (last_error == I2C_ERROR_CONTINUE)?I2C_ERROR_OK:last_error; // Don't return Continue for compatibility.
 }
 
 /* @stickBreaker 11/2017 fix for ReSTART timeout, ISR
@@ -191,12 +192,19 @@ uint8_t TwoWire::requestFrom(uint16_t address, uint8_t size, bool sendStop)
 
     last_error = readTransmission(address, &rxBuffer[cnt], size, sendStop, &cnt);
     rxIndex = 0;
-    rxLength = rxQueued;
-    rxQueued = 0;
-    txQueued = 0; // the SendStop=true will restart all Queueing
-    if(last_error != I2C_ERROR_OK){
+  
+    rxLength = cnt;
+  
+    if( last_error != I2C_ERROR_CONTINUE){ // not a  buffered ReSTART operation
+      // so this operation actually moved data, queuing is done.
+        rxQueued = 0;
+        txQueued = 0; // the SendStop=true will restart all Queueing or error condition
+    }
+  
+    if(last_error != I2C_ERROR_OK){ // ReSTART on read does not return any data
         cnt = 0;
     }
+  
     return cnt;
 }
 

libraries/Wire/src/Wire.h

@@ -67,12 +67,13 @@ protected:
 public:
     TwoWire(uint8_t bus_num);
     ~TwoWire();
-    bool begin(int sda=-1, int scl=-1, uint32_t frequency=0);
+    bool begin(int sda=-1, int scl=-1, uint32_t frequency=0); // returns true, if successful init of i2c bus
+      // calling will attemp to recover hung bus
 
     void setClock(uint32_t frequency); // change bus clock without initing hardware
     size_t getClock(); // current bus clock rate in hz
 
-    void setTimeOut(uint16_t timeOutMillis);
+    void setTimeOut(uint16_t timeOutMillis); // default timeout of i2c transactions is 50ms
     uint16_t getTimeOut();
 
     uint8_t lastError();
@@ -137,6 +138,7 @@ extern TwoWire Wire1;
 
 
 /*
+V1.0.2 30NOV2018 stop returning I2C_ERROR_CONTINUE on ReSTART operations, regain compatibility with Arduino libs
 V1.0.1 02AUG2018 First Fix after release, Correct ReSTART handling, change Debug control, change begin()
   to a function, this allow reporting if bus cannot be initialized, Wire.begin() can be used to recover
   a hung bus busy condition.