Programming instructions

Sample code sequence

WO R K I N G W I T H T H E C P U

R11 and R12 registers

Use these instructions to program the TLB Lockdown register:

Function

Instruction

 

 

Read data TLB lockdown victim

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

 

 

Write data TLB lockdown victim

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

 

 

The victim automatically increments after any table walk that results in an entry being written into the lockdown part of the TLB.

Note: It is not possible for a lockdown entry to map entirely either small or large pages, unless all subpage access permissions are the same. Entries can still be written into the lockdown region, but the address range that is mapped covers only the subpage corresponding to the address that was used to perform the page table walk.

This example shows the code sequence that locks down an entry to the current victim.

ADR r1,LockAddr

;

set R1 to the value of the address to be locked down

MCR p15,0,r1,c8,c7,1

;

invalidate TLB single entry to ensure that

 

 

LockAddr is not already in the TLB

MRC p15,0,r0,c10,c0,0

;

read the lockdown register

ORR r0,r0,#1

;

set the preserve bit

MCR p15,0,r0,c10,c0,0

;

write to the lockdown register

LDR r1,[r1]

;

TLB will miss, and entry will be loaded

MRC p15,0,r0,c10,c0,0

;

read the lockdown register (victim will have

 

;

incremented

BIC r0,r0,#1

;

clear preserve bit

MCR p15,0,r0,c10,c0,0

; write to the lockdown register

R 1 1 a n d R 1 2 r e g i s t e r s

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Accessing (reading or writing) these registers causes UNPREDICTABLE behavior.

R 1 3 : P r o c e s s I D r e g i s t e r

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

The Process ID register accesses the process identifier registers. The register accessed depends on the value on the opcode_2 field:

opcode_2=0

Selects the Fast Context Switch Extension (FCSE) Process Identifier (PID)

 

register.

102Hardware Reference NS9215

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Digi NS9215 manual a n d R 1 2 r e g i s t e r s, P r o c e s s I D r e g i s t e r

NS9215 specifications

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