ARM920T datasheet(49/350 Pages) ATMEL

49 / 350 page

Programmer’s Model

ARM DDI 0151C

2-23

Table 2-19 shows the instructions you can use to access the TLB lockdown register.

Figure 2-8 shows the format of bits in register 10.

Figure 2-8 Register 10

The entries in the TLBs are replaced using a round-robin replacement policy. This is

implemented using a victim counter that counts from entry 0 up to 63, and then wraps

back round to the base value and continues counting, wrapping around to the base value

from 63 each time.

There are two mechanisms available for ensuring entries are not removed from the TLB:

•

Locking an entry down prevents it from being selected for overwriting during a

table walk. You can do this by programming the base value to which the victim

counter reloads. For example, if the bottom 3 entries (0–2) are to be locked down,

you must program the base counter to 3.

•

You can preserve an entry during an Invalidate All instruction. You can do this

by ensuring the P bit is set when the entry is loaded into the TLB. Examples that

show how you can load a single entry into the I and D TLBs at location 0, make

it immune to Invalidate All, and lock it down are shown in Example 2-3 on

page 2-24 and Example 2-4 on page 2-24.

Table 2-19 Accessing the TLB lockdown register 10

Function

Data

Instruction

Read D TLB lockdown

TLB lockdown

MRC p15,0,Rd,c10,c0,0

Write D TLB lockdown

TLB lockdown

MCR p15,0,Rd,c10,c0,0

Read I TLB lockdown

TLB lockdown

MRC p15,0,Rd,c10,c0,1

Write I TLB lockdown

TLB lockdown

MCR p15,0,Rd,c10,c0,1

26 25

20 19

1 0

Base

SBZ/UNP

Victim

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