ARM Architecture Reference Manual ARMv7-A and ARMv7-R edition

Debug Register Interfaces
DSB
ISB
; (7) Return the pointer to first word not read.
MOV R0, R4
POP {R4, PC}
Example OS Save and Restore sequences using the Extended CP14 interface
On an implementation that includes the OS Save and Restore mechanism and the Extended CP14 interface:
Example C6-3 shows the correct sequence for saving the debug logic state, using the Extended CP14
interface, before powering down
Example C6-4 on page C6-15 shows the correct sequence, using the Extended CP14 interface, for
restoring the debug logic state when the system is powered on again.
When the debug logic state is restored, if the OS Unlock Catch bit in the Event Catch Register is set to 1 a
debug event is triggered when the DBGOSLAR is cleared. This event might be used by an external debugger
to restart a debugging session. See Event Catch Register (DBGECR) on page C10-78.
Example C6-3 OS debug register save sequence, Extended CP14 interface
; On entry, R0 points to a block to save the debug registers in.
SaveDebugRegisters
; (1) Set OS Lock Access Register (DBGOSLAR).
LDR R1, =0xC5ACCE55
MCR p14, 0, R1, c1, c0, 4 ; Write DBGOSLAR
ISB
; (2) Get the number of words to save.
MRC p14, 0, R1, c1, c2, 4 ; DBGOSSRR returns size
STR R1, [R0], #4 ; Push on to the save stack
; (3) Loop reading words from the DBGOSSRR.
CMP R1, #0 ; Check for zero
SaveDebugRegisters_Loop
ITTT NE
MRCNE p14, 0, R2, c1, c2, 4 ; Load a word of data
STRNE R2, [R0], #4 ; Push on to the save stack
SUBSNE R1, R1, #1
BNE SaveDebugRegisters_Loop
; (4) Return the pointer to first word not written to. This pointer is already in R0, so
; all that is needed is to return from this function.
;
; Leave DBGOSLAR set, because from now on we do not want any changes.
BX LR
C6-14 Copyright © 1996-1998, 2000, 2004-2008 ARM Limited. All rights reserved. ARM DDI 0406B