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(1) DALc/DALp/DALo (Data Cache Auto-Lock: current/previous/old)
The three bits DALc/DALp/DALo form a three-level stack, indicating the current, previous
and old auto-lock status of the data cache. For each bit, 1 means the lock is in effect, and 0
means it is not. A Reset exception clears DALc, DALp and DALo to 0.
When the R3900 Processor Core responds to an exception, it saves the value of the current
data cache auto-lock mode (DALc) in the previous mode bit (DALp), and that of the previous
mode bit (DALp) in the old mode bit (DALo). The current data cache auto-lock mode
(DALc) is cleared to 0, disabling the data cache lock function.
These bits are valid only when a cache with lock function is implemented.
(2) IALc/IALp/IALo (Instruction Cache Auto-Lock: current/previous/old)
The three bits IALc/IALp/IALo form a three-level stack, indicating the current, previous and
old auto-lock status of the instruction cache. For each bit, 1 means the lock is in effect, and
0 means it is not. A Reset exception clears IALc, IALp and IALo to 0.
When the R3900 Processor Core responds to an exception, it saves the value of the current
instruction cache auto-lock mode (IALc) in the previous mode bit (IALp), and that of the
previous mode bit (IALp) in the old mode bit (IALo). The current instruction cache auto-
lock mode (IALc) is cleared to 0, disabling the instruction cache lock function.
These bits are valid only when a cache with lock function is implemented.