PXS20RM Datasheet, PDF (971/1368 Pages) Freescale Semiconductor, Inc – PXS20 Microcontroller

Memory Protection Unit (MPU)
where the current_pid[*] is the selected process identifier from the current bus master, and
rgdn.pid[*] and rgdn.pidmask[*] are the appropriate process identifier fields from the region
descriptor n. For AHB bus masters that do not output a process identifier, the MPU forces the pid_hit
term to be asserted.
As shown in Figure 30-10, the access evaluation macro actually forms the logical complement (hit_b) of
the combined region_hit and pid_hit boolean equations.
30.7.1.2 Access evaluation – privilege violation determination
While the access evaluation macro is making the region hit determination, the logic is also evaluating if
the current access is allowed by the permissions defined in the region descriptor. Using the AHB
hmaster[*] and hprot[1] (supervisor/user mode) signals, a set of effective permissions
(eff_rgd[r,w,x]) is generated from the appropriate fields in the region descriptor. The protection
violation logic then evaluates the access against the effective permissions using the specification shown in
Table 30-11.
Table 30-11. Protection violation definition
Description
inst fetch read
inst fetch read
data read
data read
data write
data write
Inputs
hwrite hprot[0] eff_rgd[r] eff_rgd[w] eff_rgd[x]
0
0
—
—
0
0
0
—
—
1
0
1
0
—
—
0
1
1
—
—
1
—
—
0
—
1
—
—
1
—
Output
Protection
Violation?
yes, no x permission
no, access is allowed
yes, no r permission
no, access is allowed
yes, no w permission
no, access is allowed
The resulting boolean equation for the processor protection violations is:
cpu_protection_violation
= ~hwrite & ~hprot[0] & ~eff_rgdn[x]// ifetch & no x
| ~hwrite & hprot[0] & ~eff_rgdn[r]// data_read & no r
| hwrite& ~eff_rgdn[w] // data_write& no w
The resulting boolean equation for the non-processor protection violations is:
Eqn. 30-3
protection_violation
= ~hwrite & ~eff_rgdn[r]// data_read & no r
| hwrite& ~eff_rgdn[w] // data_write& no w
Eqn. 30-4
Freescale Semiconductor
PXS20 Microcontroller Reference Manual, Rev. 1
30-17