The rtcwake binary in my KoboStuff package is patched to behave on recalcitrant i.MX boards, so it should Just Work (TM).
Just keep in mind you cannot enter suspend while Wi-Fi is enabled (that'll either hang or crash immediately or on wakeup, depending on the board).
See
KOReader's suspend logic for all the gory details (which basically boil down to writing to 2 sysfs files, and some carefully tuned timing gymnastics. The sleep matters. A lot. As does the fact that this whole thing runs 15s *after* a suspend request). That's for suspend. We implement rtcwake ourselves, so I'll spare you that bit of hellscape

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