Tlb Entry Lock Mechanism - Texas Instruments OMAP5910 Reference Manual

6.2.2.4 Protecting TLB Entries
Figure 33.

TLB Entry Lock Mechanism

SPRU890A
3) Select the TLB entry to be written by setting the victim pointer through the
Lock/Protect Entry Register (LOCK_REG). For example, to update entry
0 in the TLB, write 0 to the victim pointer field of LOCK_REG.
4) Set the WRITE_ENTRY bit in the Read/Write TLB Entry Register
(LD_TLB_REG).
5) Enable the table walking logic by setting the TWL_EN bit in the Control
Register (CNTL_REG). This step can be omitted if the table walking logic
is not used.
Section 6.5 gives detailed descriptions of all TLB control registers.
The first n TLB entries (with n < 32) can be protected, or locked, against being
overwritten with new translations retrieved by the table walking logic. This is
done by setting the TLB base pointer to n (see Figure 33). The remaining
entries are overwritten, if necessary, on a random basis. The victim pointer
indicates the next TLB entry to be read/written.
Victim pointer = 30
Base pointer = 3
Locking TLB entries ensures that certain commonly used or time-critical
translations are always in the TLB and do not have to be retrieved via the table
walking process.
To protect the first n TLB entries, follow these steps:
1) Disable the table walking logic by clearing the TWL_EN bit in the Control
Register (CNTL_REG).
2) Set the base pointer field in the Lock/Protect Entry Register (LOCK_REG)
to n, and set the current victim pointer (also in the Lock/Protect Entry
Register) to a value equal to or greater than n. For example, to protect
DSP Memory Management Unit
TLB
Entry 31
Entries 3...31 can be
Entry 3
Entry 2
Entry 1
Entries 0,1, and 2 are
Entry 0
DSP Subsystem
overwritten
locked
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