Digi NS9215 - Manual (Page 102)

W O R K I N G W I T H T H E C P U
R11 and R12 registers
102 Hardware Reference NS9215
Programming
instructions
Use these instructions to program the TLB Lockdown register:
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.
Sample code
sequence
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
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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:
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
opcode_2=0 Selects the Fast Context Switch Extension (FCSE) Process Identifier (PID)
register.