- Generalize ... it's not just for PC/AT style RTCs, and there
may be more than one RTC per system.
- Not all RTCs expose the same feature set as PC/AT ones; most
of these ioctls will be rejected by some RTCs.
- Be explicit about when {A,P}IE_{ON,OFF} calls are needed.
- Describe the parameter to the get/set epoch request; correct
the description of the get/set frequency parameter.
- Document RTC_WKALM_{RD,SET}, which don't need AIE_{ON,OFF} and
which support longer alarm periods.
- Hey, not all system clock implementations count timer irqs any
more now that the new RT-derived clock support is merging.