Motorola MC68030 User Manual page 345

v =
'RP' OTHERWISE
fCl"'~
OTHERWISE
lASUIZE
=
4 LAST SIZE
=
8
- .,kFORM LIMIT CHECK)
l/U = 0 l/U = 1
L
l
( R:r
~
";
~AITh::E"Y::::~<
l i M I T
~Am'l ~IN
)
Figure 9-28. Limit Check Procedure Flowchart
9.5.5
Protection
M68000 Family processors provide an indication of the context in which they
are operating on a cycle-by-cycle basis by means ofthe function code signals.
These signals identify accesses to the user program space, the user data
space, the supervisor program space, and the supervisor data space. The
function code signals can be used for protection mechanisms by setting the
function code lookup (FCL) bit in the translation control (TC) register.
The MC68030 MMU provides the capability for separate translation trees for
supervisor and user spaces to be used. When the supervisor root pointer
enable bit (5RE) in the TC register is set, the root pointer register for the
supervisor space translation tree is selected for supervisor program or data
accesses.
The translation table trees contain both mapping and protection information.
Each table and page descriptor includes a write-protect (WP) bit, which can
be set to provide write protection at any level. Each long-format table and
page descriptor also contains a supervisor-only (5) bit, which can limit access
to programs operating at the supervisor privilege level.
MOTOROLA
MC68030 USER'S MANUAL 9-43