
6-32
G2 PowerPC Core Reference Manual
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MOTOROLA
Page Table Search Operation
6.5.2.1
Resources for Table Search Operations
In addition to setting up the translation page tables in memory, the system software must
assist the processor in loading PTEs into the on-chip TLBs. When a required TLB entry is
not found in the appropriate TLB, the processor vectors to one of the three TLB miss
exception handlers so that the software can perform a table search operation and load the
TLB. When this occurs, the processor automatically saves information about the access and
the executing context. Table 6-9 provides a summary of the implementation-specific
exceptions, registers, and instructions that can be used by the TLB miss exception handler
software in G2 core systems. Refer to Chapter 5, “Exceptions,” for more information about
exception processing.
Table 6-9. Implementation-Specific Resources for Table Search Operations
Resource
Name
Description
Exceptions
Instruction TLB miss
exception
(vector offset 0x1000)
No matching entry found in ITLB
Data TLB miss on load
exception
(vector offset 0x1100)
No matching entry found in DTLB for a load data access
Data TLB miss on store
exception—also caused
when changed bit must
be updated
(vector offset 0x1200)
No matching entry found in DTLB for a store data access or matching DLTB
entry has C = 0 and access is a store
Registers
IMISS and DMISS
When a TLB miss exception occurs, the IMISS or DMISS register contains
the 32-bit effective address of the instruction or data access that caused the
miss exception.
ICMP and DCMP
The ICMP and DCMP registers contain the word to be compared with the
first word of a PTE in the table search software routine to determine if a PTE
contains the address translation for the instruction or data access. The
contents of ICMP and DCMP are automatically derived by the core when a
TLB miss exception occurs.
HASH1 and HASH2
The HASH1 and HASH2 registers contain the primary and secondary PTEG
addresses that correspond to the address causing a TLB miss. These
PTEG addresses are automatically derived by the core by performing the
primary and secondary hashing function on the contents of IMISS or
DMISS, for an ITLB or DTLB miss exception, respectively.
RPA
The system software loads a TLB entry by loading the second word of the
matching PTE entry into the RPA register and then executing the
tlbli
or
tlbld
instruction (for loading the ITLB or DTLB, respectively).
Instructions
tlbli r
B
Loads the contents of the ICMP and RPA registers into the ITLB entry
selected by <ea> and SRR1[WAY]
tlbld r
B
Loads the contents of the DCMP and RPA registers into the DTLB entry
selected by <ea> and SRR1[WAY]
F
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