ATmega2560 is little endian or big endian?

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1

Hi Team,
I want to know Atmega2560 is little endian or big endian, i searched on internet but not found exactly about ATmega2560, only i found that most of AVR microcontrollers are little endian, with this info i am proceeding my project. But i want concrete info on ATmega2560 about its endianness. Please help me to get this info.

2 
#include <Arduino.h>

#include <limits.h>
#include <stdint.h>

#if CHAR_BIT != 8
#error "unsupported char size"
#endif

enum
{
    O32_LITTLE_ENDIAN = 0x03020100ul,
    O32_BIG_ENDIAN = 0x00010203ul,
    O32_PDP_ENDIAN = 0x01000302ul
};

static const union { unsigned char bytes[4]; uint32_t value; } o32_host_order =
    { { 0, 1, 2, 3 } };

#define O32_HOST_ORDER (o32_host_order.value)

void setup() 
{
  Serial.begin( 115200 );

  if ( O32_HOST_ORDER == O32_LITTLE_ENDIAN )
  {
    Serial.println( F( "Little Endian" ) );
  }
  else if ( O32_HOST_ORDER == O32_BIG_ENDIAN )
  {
    Serial.println( F( "Big Endian" ) );
  }
  else if ( O32_HOST_ORDER == O32_PDP_ENDIAN )
  {
    Serial.println( F( "PDP Endian" ) );
  }
  else
  {
    Serial.println( F( "Other Endian" ) );
  }
}

void loop() {
  // put your main code here, to run repeatedly:

}

According to the code above the ATtiny861 is...
Little Endian

3

I wonder does PDP_ENDIAN derive from DEC PDP11 mini-computers. We had one in work with a HUGE 10MB drive.

More interestingly how can there be three types of endian-ness?

...R

4

Robin2:
I wonder does PDP_ENDIAN derive from DEC PDP11 mini-computers. We had one in work with a HUGE 10MB drive.

More interestingly how can there be three types of endian-ness?

...R

Based on the code above, it appears that the long word has words with wierd endianness
Instead of 3,2,1,0 or 0,1,2,3 it goes 1,0,3,2.

5

And now you get a 2 TB drive that can sit on your hand and be taken with you!

I imagine you can take a long number and send out the bytes in any order you want, with MSB or LSB first, so 32 combinations? More if you provide MSB/LSB swapping.

6

Robin2:
I wonder does PDP_ENDIAN derive from DEC PDP11 mini-computers. We had one in work with a HUGE 10MB drive.

More interestingly how can there be three types of endian-ness?

...R

Yes. The PDP-11 floating point format swapped the bytes in each of the two 16-bit words, but the words themselves were not swapped:

If you do:

unsigned long a = 0x01020304U;

the value with be bytes 4, 3, 2, 1 if you look at them individually. On a big endian system, the bytes would be 1, 2, 3, 4. On a mixed endian system like the PDP-11 floating point format, the bytes would be 2, 1, 4, 3.

7

Thanks for reply....
i used that code and i got confirm its little endian.