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Memory Management Unit (MMU)
4-22
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Binary state bits are updated on all TLB write (load) operations, as well as normal non-locked entries ITLB
and DTLB hits. Also, if all entries in a binary state are locked, then that state is always set. That is, if entries
15, 14, 13, and 12 were locked, LRU state bit rdRecent15To14 is forced to 1.
For a completely valid TLB, binary state information determines the LRU entry. The replacement
algorithm is deterministic and, for the case of a full TLB (with no locked entries and always touching new
pages), the replacement entry repeats every 32 TLB loads.
4.3.8.3
TLB Locked Entries
is a ColdFire MMU Harvard TLB block diagram.
For TLB miss faults, the instruction restart model re-executes an instruction on returning from the
exception handler. An instruction can touch two instruction pages (a 32- or 48-bit instruction can straddle
two pages) or four data pages (a memory-to-memory word or longword move where misaligned source
and destination operands straddle two pages). Therefore, one instruction may take two ITLB misses and
allocate two ITLB pages before completion. Likewise, one instruction may require four DTLB misses and
allocate four DTLB pages. Because of this, a pool of unlocked TLB entries must be available if virtual
memory is used.
The above examples show the fewest entries needed to guarantee an instruction can complete execution.
For good MMU performance, more unlocked TLB entries should be available.
rdRecent25
A 1 indicates 25 is more recent than 24
rdRecent23
A 1 indicates 23 is more recent than 22
rdRecent21
A 1 indicates 21 is more recent than 20
rdRecent19
A 1 indicates 19 is more recent than 18
rdRecent17
A 1 indicates 17 is more recent than 16
rdRecent15
A 1 indicates 15 is more recent than 14
rdRecent13
A 1 indicates 13 is more recent than 12
rdRecent11
A 1 indicates 11 is more recent than 10
rdRecent09
A 1 indicates 09 is more recent than 08
rdRecent07
A 1 indicates 07 is more recent than 06
rdRecent05
A 1 indicates 05 is more recent than 04
rdRecent03
A 1 indicates 03 is more recent than 02
rdRecent01
A 1 indicates 01 is more recent than 00
Table 4-14. PLRU State Bits (continued)
State Bits
Meaning
Summary of Contents for MCF54455
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Page 125: ...Freescale Semiconductor 1 ...
Page 145: ...Enhanced Multiply Accumulate Unit EMAC 5 21 Freescale Semiconductor ...
Page 173: ...Cache 6 28 Freescale Semiconductor ...
Page 179: ...Static RAM SRAM 7 6 Freescale Semiconductor ...
Page 207: ...Power Management 9 16 Freescale Semiconductor ...
Page 323: ...Reset Controller Module 13 8 Freescale Semiconductor ...
Page 389: ...Pin Multiplexing and Control 16 44 Freescale Semiconductor ...
Page 575: ...PCI Bus Controller 22 58 Freescale Semiconductor ...
Page 600: ...Advanced Technology Attachment ATA Freescale Semiconductor 23 25 ...
Page 601: ...Freescale Semiconductor 1 ...
Page 842: ...I2 C Interface Freescale Semiconductor 33 16 ...
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Page 921: ...Revision History A 6 Freescale Semiconductor ...