Building an avr64db28 project with avr-gcc

1. Download and install latest avr-gcc https://github.com/ZakKemble/avr-gcc-build/releases
2. Download and unzip latest Atmel support package from http://packs.download.atmel.com/
   e.g. http://packs.download.atmel.com/Atmel.AVR-Dx_DFP.2.2.253.atpack
3. Build c/c++ files with the following options:
   • C++:
     avr-g++ -D__AVR_DEV_LIB_NAME__=avr64db28 -I<Atmel.AVR-Dx_DFP>/include -mmcu=avr64db28 -B <Atmel.AVR-Dx_DFP>/gcc/dev/avr64db28
   • C:
     avr-gcc -D__AVR_DEV_LIB_NAME__=avr64db28 -I<Atmel.AVR-Dx_DFP>/include -mmcu=avr64db28 -B <Atmel.AVR-Dx_DFP>/gcc/dev/avr64db28
   • ASM:
     avr-g++ -c -D__AVR_DEV_LIB_NAME__=avr64db28 -I<Atmel.AVR-Dx_DFP>/include -mmcu=avr64db28 -B <Atmel.AVR-Dx_DFP>/gcc/dev/avr64db28
   • Linker:
     avr-g++ -mmcu=avr64db28 -B <Atmel.AVR-Dx_DFP>/gcc/dev/avr64db28 -Wl,--start-group -Wl,-lm -Wl,--end-group -Wl,--gc-sections -Wl,--defsym,__DATA_REGION_LENGTH__=0x6000

Note
__DATA_REGION_LENGTH__=0x6000 is needed to workaround address 0x806001 of avr64db section .bss is not within region data caused by mismatching avr-gcc linker script and the chip definition from the support package.

Details
Address 0x806000 is set by spec-avr64db28

*link_data_start:
	%{!Tdata:-Tdata 0x806000}

While the linker script avrxmega2.x defines

data   (rw!x) : ORIGIN = 0x802000, LENGTH = __DATA_REGION_LENGTH__

Datasheet defines SRAM memory map

Data space	Range
(Reserved)	0x1600-0x3FFF
SRAM 16 KB	0x4000-0x7FFF

Perhaps 0x802000 is a base address for the entire xmega2 family, while 0x806000 could be a valid start for the data section in avr64db28. However, the memory range communicated to the linker:

data             0x0000000000802000 0x0000000000002000 rw !x

is not valid for avr64db28. The __DATA_REGION_LENGTH__=0x6000 parameter makes it

data             0x0000000000802000 0x0000000000006000 rw !x

Now data includes 0x806000 and the linker succeeds. Although it is not clear what is the use of 0x4000-0x5FFF memory range