This attribute indicates which bank will be running when the shelf
is reset or powered-down and then powered-up.
writable: Indicates the writable bank will be the bank on the next
power up or reset.
fixed: Indicates the fixed bank will be the bank on the next power
up or reset.
unknown: The software has not yet determined which is the bank
on shelf restart. This normally takes a few seconds when the
software is first activated.