Compatibiliy with AtMega4808 under MegaCoreX /w SoftwareSerial about serialtransfer

[PowerBroker2]

Looks like an "endian" difference between the two MCUs. Try swapping the byte order on the ints on the receiver and see if it helps. Might also be useful to set the int size manually.

[adelin-mcbsoft]

Both MCUs report being "Little Endian".
I ran the following code to find out:

#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" ) );
  }
}

So that might not be it.
It also fails with floats, not only ints.
Weird thing that the CRC validates the packets, so has to be some bit-shifting issue, just can't figure out what...