Although firmware has proven to be fairly reliable i.e. it successfully communicated with the host, it worked properly only when run on the MSP430F5529 evaluation-kit. When uploaded to the target device (depicted somewhere on the photo on the far left) it would not make the device to enumerate, and there is no sign of an USB communication whatsoever (other than that, the firmware runs). The whole pull-up resistor thing that I described earlier didn't help, so after debugging further I discovered fatal mistake I made : I mixed up the XT1 and XT2 oscillator inputs :( So for now I have board which would feed RTC with 4MHz signal (if I only used the RTC), and has main oscillator without a crystal. Will try to feed the clock signal in "bypass-mode" directly from a generator when I only get back home.