Memory Protection Unit (MPU)
MPC5644A Microcontroller Reference Manual, Rev. 6
268
Freescale Semiconductor
Because the region descriptor is a 128-bit entity, there are potential coherency issues as this structure is
being updated because multiple writes are required to update the entire descriptor. Accordingly, the MPU
hardware assists in the operation of the descriptor valid bit to prevent incoherent region descriptors from
generating spurious access errors. In particular, it is expected that a complete update of a region descriptor
is typically done with sequential writes to MPU_RGD
n
.Word0, then MPU_RGD
n
.Word1, ... and
MPU_RGD
n
.Word3. The MPU hardware automatically clears the valid bit on any writes to words {0,1,2}
of the descriptor. Writes to this word set/clear the valid bit in a normal manner.
Because it is also expected that system software may adjust the access controls within a region descriptor
(MPU_RGDn.Word2) only as different tasks execute, an alternate programming view of this 32-bit entity
is provided. If only the access controls are being updated, this operation must be performed by writing to
MPU_RGDAAC
n
(alternate access control
n
) as stores to these locations do not affect the descriptor’s
valid bit.
Address: MPU_BASE (0xFFF1_0000) + 0x400 + (16*
n
) + 0xc (MPU_RGD
n
.Word3)
Access: User read/write
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
R
PID
PIDMASK
W
Reset
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
R
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
VLD
W
Reset
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
= not implemented
Figure 13-7. MPU Region Descriptor n, Word 3 Register (MPU_RGDn.Word3)
Table 13-9. MPU_RGDn Word 3 field description
Field
Description
0–7
PID
Process Identifier
This 8-bit field specifies that the optional process identifier is to be included in the determination of
whether the current access hits in the region descriptor. This field is combined with the PIDMASK and
included in the region hit determination if MPU_RGD
n
.Word2[MxPE] is set.
Summary of Contents for MPC5644A
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