Memory Management Unit
MPC885 PowerQUICC Family Reference Manual, Rev. 2
Freescale Semiconductor
8-5
Figure 8-2. Flow of Load/Store Access
8.3.3
TLB Operation
Each TLB contains pointers to pages in physical memory where data is indexed by the EPN. TLBs entries
can have different page sizes. The entry page size determines which EA bits are compared and how many
of its lsbs pass untranslated as physical address bits.
For a 4-Kbyte page, four subpage validity flags are supported, allowing any combination of 1-Kbyte
subpages to be mapped. For any other page size, all of these flags should have the same value.
Programming non-4-Kbyte pages with different valid bits is a programming error. Subpage validity flags
can be manipulated to implement 1–4-Kbyte pages or any other combination of 1-Kbyte subpages.
However, all subpages of an effective page frame must map to the same physical page. During translation,
the EA, the privilege level (MSR[PR]), and CASID are provided to the TLB, as shown in
Figure 8-3
. In
the TLB, the EA and CASID are compared with each entry’s EPN and ASID. The CASID is compared
only when the matching entry is programmed as unshared. See
Table 8-12
and
Table 8-13
.
Data/Instruction Fetch
TLB
Hit
?
TLB reload (read page
description from external
memory to TLB)
Yes
No
32-bit EA is generated
Compare address
with TLB
entries
Is page
valid
?
Yes
No
TLB Error Exception
Access permitted
by page protection
?
Yes
No
Use page description from TLB
(0 clock penalty)
(20–23 clock penalty
@ one wait-state
external memory)
Содержание PowerQUICC MPC870
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Страница 780: ...SCC Ethernet Mode MPC885 PowerQUICC Family Reference Manual Rev 2 27 24 Freescale Semiconductor ...
Страница 794: ...SCC Transparent Mode MPC885 PowerQUICC Family Reference Manual Rev 2 28 14 Freescale Semiconductor ...
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Страница 882: ...Universal Serial Bus USB MPC885 PowerQUICC Family Reference Manual Rev 2 31 34 Freescale Semiconductor ...
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Страница 1004: ...Buffer Descriptors and Connection Tables MPC885 PowerQUICC Family Reference Manual Rev 2 37 30 Freescale Semiconductor ...
Страница 1022: ...ATM Parameter RAM MPC885 PowerQUICC Family Reference Manual Rev 2 38 18 Freescale Semiconductor ...
Страница 1068: ...ATM Pace Control MPC885 PowerQUICC Family Reference Manual Rev 2 40 22 Freescale Semiconductor ...
Страница 1090: ...UTOPIA Interface MPC885 PowerQUICC Family Reference Manual Rev 2 43 8 Freescale Semiconductor ...
Страница 1120: ...AAL2 Implementation MPC885 PowerQUICC Family Reference Manual Rev 2 44 30 Freescale Semiconductor ...
Страница 1162: ...Fast Ethernet Controller FEC MPC885 PowerQUICC Family Reference Manual Rev 2 45 40 Freescale Semiconductor ...
Страница 1172: ...SEC Lite Overview MPC885 PowerQUICC Family Reference Manual Rev 2 46 8 Freescale Semiconductor ...
Страница 1176: ...SEC Lite Address Map MPC885 PowerQUICC Family Reference Manual Rev 2 47 4 Freescale Semiconductor ...
Страница 1214: ...SEC Lite Execution Units MPC885 PowerQUICC Family Reference Manual Rev 2 48 38 Freescale Semiconductor ...
Страница 1312: ...Byte Ordering MPC885 PowerQUICC Family Reference Manual Rev 2 A 8 Freescale Semiconductor ...
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