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ARM DDI 0363E Copyright © 2009 ARM Limited. All rights reserved. 11-22
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11.4.11 Debug Run Control Register
The DRCR requests the processor to enter or leave debug state. It also clears the sticky
exception bits present in the DSCR.
Figure 11-9 shows the bit arrangement of the DRCR.
Figure 11-9 Debug Run Control Register format
Table 11-15 shows how the bit values correspond with the Debug Run Control Register
functions.
31
053
Reserved
Cancel memory request
214
Clear sticky pipeline advance
Clear sticky exceptions
Restart request
Halt request
Table 11-15 Debug Run Control Register functions
Bits Field Function
[31:5] Reserved RAZ.
[4] Cancel memory
requests
If 1 is written to this bit, the processor abandons any pending memory transactions until it
can enter debug state. Debug state entry is the acknowledge event that clears this request.
Abandoned transactions have the following behavior:
• abandoned stores might write an Unpredictable value to the target address
• abandoned loads return an Unpredictable value to the register bank.
An abandoned transaction does not cause any exception. Additional instruction fetches or
data accesses after the processor entered debug state have an Unpredictable behavior.
This bit enables the debugger to progress on a deadlock so the processor can enter debug
state. For a debug state entry to occur, a halting debug event must be requested before this
bit is set. If you write a 1 to this bit when DBGEN is LOW, the write has no effect.
a
[3] Clear sticky
pipeline advance
Writing a 1 to this bit clears DSCR[25].
[2] Clear sticky
exceptions
Writing a 1 to this bit clears DSCR[8:6].
[1] Restart request Writing a 1 to this bit requests that the processor leaves debug state. This request is held
until the processor exits debug state. When the debugger makes this request, it polls
DSCR[1] until it reads 1. This bit always reads as zero. Writes are ignored when the
processor is not in debug state.
[0] Halt request Writing a 1 to this bit triggers a halting debug event, that is, a request that the processor
enters debug state. This request is held until the debug state entry occurs. When the
debugger makes this request, it polls DSCR[0] until it reads 1. This bit always reads as zero.
Writes are ignored when the processor is already in debug state.
a. Entry into debug state is not expected to be recoverable.