Mostek MK48T0x battery-backed realtime
nvram0 at syscon0 offset 0x80000
nvram driver provides support for the
Mostek MK48T02 realtime clock chip.
In addition to the clock itself, this chip embeds 2KB of battery-backed memory, which is accessible through the special /dev/nvram0 file.
The last 8 bytes of the battery-backed memory contains the realtime clock registers. Writing to these locations will interfere with proper clock operation.
Most, if not all, of the battery-backed memory is used by DG/UX to
store some of its configuration data, and may be reinitialized by the PROM
if it considers the memory contents as invalid. The
nvram driver does not prevent access to this