MOTOROLA
Chapter 9. Memory Management Unit (MMU)
9-33
Part II. PowerPC Microprocessor Module
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The TLB entry is written by loading the tablewalk level-two entry value to Mx_RPN.
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A scratch register, M_TW, is provided in addition to the architecture-deÞned
SPRG0ÐSPRG3, so miss code need not corrupt existing GPRs.
9.10.1.1 Translation Reload Examples
The following examples reload a TLB entry using a two-level tree page table structure. In
both examples, M_TWB holds the base pointer to the Þrst-level table and data and
instruction address translation are turned off. Figure 9-23 performs a DTLB reload.
Figure 9-23. DTLB Reload Code Example
Figure 9-24 performs an ITLB reload
Figure 9-24. ITLB Reload Code Example
9.10.2 Locking TLB Entries
Four entries in each TLB can be made unavailable to the replacement algorithm, thus
enabling the user to lock translation entries into them by specially conÞguring the TLB
replacement counters.
dtlb_swtw
mtspr
M_TW, R1
# Save R1
mfspr
R1, M_TWB
# Load R1 with level-1 pointer
lwz
R1, (R1)
# Load level-1 page entry
mtspr
MD_TWC,R1
# Save level-2 base pointer and level-1 attributes
mfspr
R1, MD_TWC
# Load R1 with level-2 pointer while taking page
# size into account
lwz
R1, (R1)
# Load level-2 page entry
mtspr
MD_RPN, R1
# Write TLB entry
mfspr
R1, M_TW
# Restore R1
rfi
itlb_swtw
mtspr
M_TW, R1
# Save R1
mfspr
R1, SRR0
# Load R1 with instruction miss EA (the same data
# may be taken from MI_EPN)
mtspr
MD_EPN, R1
# Save instruction miss EA in MD_EPN
mfspr
R1, M_TWB
# Load R1 with level-1 pointer
lwz
R1, (R1)
# Load level-1 page entry
mtspr
MI_TWC,R1
# Save level-1 attributes
mtspr
MD_TWC,R1
# Save level-2 base pointer
mfspr
R1, MD_TWC
# Load R1 with level-2 pointer while taking page
# size into account
lwz
R1, (R1)
# Load level-2 page entry
mtspr
MI_RPN, R1
# Write TLB entry
mfspr
R1, M_TW
# Restore R1
rfi
Содержание MPC860 PowerQUICC
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