Saving data in a globally declared float array

Question

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

This is the output of avr-size:

 text data bss dec hex
 55828 3906 2978 62712 f4f8

Is it a memory related problem?

• Ignacio Vazquez-Abrams: What does avr-size say about the final executable?
• UserK: @IgnacioVazquez-Abrams Please see the output of the command
• Omer: Are you doing any dynamic memory allocations? can you post the full code?
• Nick Gammon: Please post a Minimal, Complete, and Verifiable example. Not seeing the data declarations, nor the value of sizeBuffAcc it is impossible to tell what the issue is.

Answer 1

The ATmega328P has 2kiB of SRAM. Your program uses almost 3kiB. Move strings and constant values into flash.

• UserK: Thanks for the suggestion but I'm using the Mega 2560 which has 8KB of SRAM.
• UserK: I will modify the sketch with PROGMEM as you suggested.