Somewhat a continuation from this thread.
The 3.6.2 toolchain, seems to support the m4809 but not the AVR128Dx. Specifically, this link (which was from the atpack.) Shows NVMCTRL_CMD_PAGEERASEWRITE_gc
the EEPROM write functions available in the 3.6.2 toolchain support NVMCTRL_CMD_PAGEERASEWRITE_gc.
When I compile for the AVR128DA it finds the ‘NVMCTRL_CMD_PAGEERASEWRITE_gc’ undeclared. Looking at the ioavr128da28.h it is clear the Non-volatile Memory Controller commands are different.
I can't even find the 3.6.2 source now, but it got packaged on Debian, so that is what I referenced. I guess there is little chance of finding the source for eewr_block_xmega.c that works with the AVR128Dx.