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This is the output of avr-size:

   text    data     bss     dec     hex
  55828    3906    2978   62712    f4f8

I'm trying to send 60 float values via serial. Numbers are provided by an accelerometer and saved in a 240 bytes-long array. The array has been declared globally

 float buffXAccToSend[20];
 [...]
 collect()
 {
  if (storeAccData)
  {
    // Filling Buff 
     buffXAccToSend[contBuffAcc-1] = accX;   
     contBuffAcc++;
  }

  // After 60 values call sendBuffAcc()
  if (contBuffAcc%(sizeBuffAcc+1) == 0) 
   {
    sendBuffAcc();
    accDataReady=true; 
   }
 }
 [...]

This array is then copied in a structure called and the sent via serial byte by byte.. Because of buffer's dimension constraints, the message is sent 20 values at the time.

Here is the function that creates messages to send via serial

void sendBuffAcc()
{
  int stepCont = 1;

  // Data are store in a structure and then sent
  MyShortCommand * pMyCmdShort = (MyShortCommand *)(&bufferAcc[sizeof(MyControlHdr)]);

  for (int i=0;i<sizeBuffAcc;i++)    
  {
    numFilterValuesToSend++;    
    
    pMyCmdShort->cmd = accValuesID;  
    pMyCmdShort->param1 = buffXAccToSend[i];  
 
    // You can find the output of this loop at the end of the question
    if (printAckCommands)
    {
      Serial.print(" CMD number: ");
      Serial.println(stepCont);
      Serial.println(pMyCmdShort->param1);
      Serial.println(); 
    }     
    pMyCmdShort++;
     
    // checks whether all values have been added to the message or the 
     // content has reached the maximum dimension 'maxLengthMess'
    if (stepCont%(maxLengthMess) == 0 || stepCont == sizeBuffAcc)
    {
      sendCommandToMatlabFilter();          
    }    
   }
  stepCont++;
 }
 storeAccData = false;
 contBuffAcc=1;      
}

The problem The content of buffXAccToSend is correct in the collect() function but when I use it in the sendBuff() function it data after the 26th float are all 0.

The content of a the 60 float long array, buffXAccToSend:

val: 20    -0.00
val: 21    0.02
val: 22    0.02
val: 23    0.01
val: 24    -0.02
val: 25    -0.02  
val: 26    0.00
val: 27    0.03
val: 28    -0.01
val: 29    -0.00
val: 30    0.01
val: 31    -0.00
val: 32    -0.01
val: 33    0.00
val: 34    0.01
val: 35    0.02
val: 36    0.02
val: 37    -0.00
val: 38    -0.00
val: 39    0.00
val: 40    0.00

And here is the output of the for loop inside the sendBuff()

Sending # commands:20
 CMD number: 21
-0.00

 CMD number: 22
0.02

 CMD number: 23
0.02

 CMD number: 24
0.01
 
 CMD number: 25
-0.02

 CMD number: 26
-0.02
 
 CMD number: 27  // From now on values are all zero! Why?
0.00
 
 CMD number: 28
0.00
 
 CMD number: 29
0.00
 
[...]

 CMD number: 59
0.00

I've also tried passing the array as an argument like sendBuff(buffXAccToSend) but it didn't work. Is it a memory related problem?

I'm trying to send 60 float values via serial. Numbers are provided by an accelerometer and saved in a 240 bytes-long array. The array is sent to a function and these values are then copied in a structure.

The problem The content of the array is still correct when the function is called. Then, when I copy it in the structure, something wrong happens and data are modified after the 26th float.

Where does the modification of an array of floats take place?

void sendBuffAcc(float a[])
{
  int stepCont = 1;
 
  // Prints the content of the globally defined array buffXAccToSend
  Serial.println();      
  for (int i=0;i<sizeBuffAcc;i++)    
  {   
    Serial.print("val: ");
    Serial.print(i);
    Serial.print("    ");
    Serial.println(buffXAccToSend[i]);
  }
  Serial.println();            

  MyShortCommand * pMyCmdShort = (MyShortCommand *)(&bufferAcc[sizeof(MyControlHdr)]);

  for (int i=0;i<sizeBuffAcc;i++)    
  {
    Serial.print("val: ");
    Serial.print(i);
    Serial.print("| Global Array:");
    Serial.println(buffXAccToSend[i]);

    numFilterValuesToSend++;    
    
    pMyCmdShort->cmd = accValuesID;  
    pMyCmdShort->param1 = a[i];  
    pMyCmdShort->param2 = 0;
    pMyCmdShort->param3 = 0;
    pMyCmdShort->param4 = 0;
 
    Serial.print("|   Param: ");
    Serial.print(pMyCmdShort->param1);
    Serial.print("|   Array:");
    Serial.println(a[i]); 

    // Move the pointer to save data in next positions
    pMyCmdShort++;
  } 
  stepCont++;
 }
 storeAccData = false;
 contBuffAcc=1;      
}

First, the content of the global array buffXAccToSend is printed via serial, then the i-th elements of a[i] and the value assigned to the pMyCmdShort->param1. This is the output:

val: 0    -0.00
val: 1    -0.00
val: 2    0.01
val: 3    -0.01
val: 4    0.04
val: 5    0.00
val: 6    0.01
val: 7    0.03
val: 8    0.01
val: 9    -0.00
val: 10    0.00
val: 11    -0.01
val: 12    -0.00
val: 13    0.01
val: 14    -0.02
val: 15    0.03
val: 16    0.00
val: 17    0.02
val: 18    -0.01
val: 19    0.00
val: 20    0.00
val: 21    -0.00
val: 22    -0.01
val: 23    -0.01
val: 24    0.01
val: 25    0.01
val: 26    -0.00
val: 27    0.03
val: 28    -0.01
val: 29    -0.00
val: 30    0.04
val: 31    -0.01
val: 32    0.01 

val: 0| Global Array: 0.01|  Param: 0.01|  Array: 0.01
val: 1| Global Array: 0.01|  Param: 0.01|  Array: 0.01
val: 2| Global Array: -0.01|  Param: -0.01|  Array: -0.01
val: 3| Global Array: -0.02|  Param: -0.02|  Array: -0.02
val: 4| Global Array: 0.02|  Param: 0.02|  Array: 0.02
val: 5| Global Array: 0.01|  Param: 0.01|  Array: 0.01
val: 6| Global Array: 0.01|  Param: 0.01|  Array: 0.01
val: 7| Global Array: 0.01|  Param: 0.01|  Array: 0.01
val: 8| Global Array: 0.04|  Param: 0.04|  Array: 0.04
val: 9| Global Array: 0.00|  Param: 0.00|  Array: 0.00
val: 10| Global Array: 0.01|  Param: 0.01|  Array: 0.01
val: 11| Global Array: -0.00|  Param: -0.00|  Array: -0.00
val: 12| Global Array: -0.01|  Param: -0.01|  Array: -0.01
val: 13| Global Array: 0.00|  Param: 0.00|  Array: 0.00
val: 14| Global Array: -0.02|  Param: -0.02|  Array: -0.02
val: 15| Global Array: -0.02|  Param: -0.02|  Array: -0.02
val: 16| Global Array: 0.00|  Param: 0.00|  Array: 0.00
val: 17| Global Array: -0.02|  Param: -0.02|  Array: -0.02
val: 18| Global Array: 0.00|  Param: 0.00|  Array: 0.00
val: 19| Global Array: 0.03|  Param: 0.03|  Array: 0.03
val: 20| Global Array: -0.01|  Param: -0.01|  Array: -0.01
val: 21| Global Array: 0.00|  Param: 0.00|  Array: 0.00
val: 22| Global Array: 0.01|  Param: 0.01|  Array: 0.01
val: 23| Global Array: 0.01|  Param: 0.01|  Array: 0.01
val: 24| Global Array: -0.01|  Param: -0.01|  Array: -0.01
val: 25| Global Array: -0.02|  Param: -0.02|  Array: -0.02
val: 26| Global Array: 0.00|  Param: 0.00|  Array: 0.00
val: 27| Global Array: 0.00|  Param: 0.00|  Array: 0.00
val: 28| Global Array: 0.00|  Param: 0.00|  Array: 0.00
val: 29| Global Array: 0.00|  Param: 0.00|  Array: 0.00
val: 30| Global Array: 0.00|  Param: 0.00|  Array: 0.00
val: 31| Global Array: 0.00|  Param: 0.00|  Array: 0.00
val: 32| Global Array: 0.00|  Param: 0.00|  Array: 0.00

Is it a memory related problem?