Freescale Semiconductor MPC5553, Справочное руководство

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MPC5553/MPC5554 Microcontroller Reference Manual, Rev. 5
3-14 Freescale Semiconductor
of the TLB entry, that TLB entry is a candidate for a possible translation match. In addition to a match in
the EPN field and TS, a matching TLB entry must match with the current process ID of the access (in
PID0), or have a TID value of 0, indicating the entry is globally shared among all processes.
Figure 3-4 shows the translation match logic for the effective address plus its attributes, collectively called
the virtual address, and how it is compared with the corresponding fields in the TLB entries.
Figure 3-4. Virtual Address and TLB-Entry Compare Process
3.3.1.3 Effective to Real Address Translation
Instruction accesses are generated by sequential instruction fetches or due to a change in program flow
(branches and interrupts). Data accesses are generated by load, store, and cache management instructions.
The instruction fetch, branch, and load/store units generate 32-bit effective addresses. The MMU translates
this effective address to a 32-bit real address which is then used for memory accesses.
Figure 3-5 shows
the effective to real address translation flow.
Figure 3-5. Effective to Real Address Translation Flow
TLB entry Hit
=0?
private page
shared page
=?
=?
TLB_entry[V]
TLB_entry[TS]
AS (from MSR[IS] or MSR[DS])
Process ID
TLB_entry[TID]
TLB_entry[EPN]
EA page number bits
=?
32-bit Effective Address
32-bit Real Address
Virtual Address
PID Effective Page Address Offset
0 31
TLB
multiple-entry
MSR[IS] for instruction fetch
AS
MSR[DS] for data access
RPN field of matching entry
n–1 n
Real Page Number Offset
0 31
NOTE: n = 32–log
2
(page size)
n

20
n = 20 for 4-Kbyte page size.
n–1 n