The Everdrive GB x7's MBC3 RTC implementation has some bugs.
with this testROM:
https://github.com/aaaaaa123456789/rtc3test/tree/developthe following tests fail:
(basic tests all pass)
range tests:
all bits clear pass
all bits set fail
valid bits (fluctuate between pass, fail h, and fail hs)
invalid value tick (fluctuate between fail and n/a)
invalid rollovers n/a
high minutes fail
high hours fail
sub-second writes:
rtcs/500 (~500.0ms)
rtcs/900 (~900.0ms)
rtc off/400 (~900.0ms)
to quote the developer on the first two sub-second writes tests:
the correct results are 1000.0ms
because writing to RTCS should reset the sub-second counter
also note:
In DMG mode, passes are black, fails are gray
of course, these all pass on an original MBC3