Hi yj L,
have you found a solution for the problem?
I'm also having trouble to get the 5775K into debug mode and read/write with Nexus after entering debug mode.
When reset is assert ,micro need waite for a long time and shift-ir "211"(bypass) before Set the OCR[DR] and OCR[WKUP] bits.
after entering debug mode，read-write sram will go wrong