Update: an implementation that is unable to save the current time as unix timestamp (for example embedded/hardware) should save the 64 bits value $7fffffff7fffffff, or equivalently, the byte values "ff ff ff 7f ff ff ff 7f" (spanning the 8 bytes in position 40-47). The reason for this is that VBA-M will ignore a timestamp in the future (will then not advance time). while VBA-M loads the timestamp as 64 bits, VBA only loads the first 4 bytes as 32 bits. the above value will be seen as "in the future" for both 32 bits and 64 bits. There is no possible timestamp that causes bgb to not try to advance time, and with such a save file, the RTC values in bgb will be undefined. Ignoring future timestamps will be supported in the next version.
offset size desc 0 4 time seconds 4 4 time minutes 8 4 time hours 12 4 time days 16 4 time days high 20 4 latched time seconds 24 4 latched time minutes 28 4 latched time hours 32 4 latched time days 36 4 latched time days high 40 4 unix timestamp when saving 44 4 0 (probably the high dword of 64 bits time), absent in the 44 bytes version