We were having issues using xboot on some XMEGA64D3 devices and found that defining USE_DFLL does not correctly enable the DFLL. For the calibration to work as intended the reference oscillator has to be started before enabling the DFLL. See also XMEGA D Manual (p. 70) "In addition, the actual clock source that is selected must enabled and configured for the calibration to function. "
We were having issues using xboot on some XMEGA64D3 devices and found that defining USE_DFLL does not correctly enable the DFLL. For the calibration to work as intended the reference oscillator has to be started before enabling the DFLL. See also XMEGA D Manual (p. 70) "In addition, the actual clock source that is selected must enabled and configured for the calibration to function. "