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ARM DDI 0363E Copyright © 2009 ARM Limited. All rights reserved. 11-51
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11.10 External debug interface
The system can access memory-mapped debug registers through the processor APB slave port.
This section describes the APB interface and the miscellaneous debug input and output signals:
• APB signals
• Miscellaneous debug signals
• Authentication signals on page 11-52.
11.10.1 APB signals
The APB slave port is compliant with the AMBA Advanced Peripheral Bus specification v3 and
can be connected to the Debug Access Port (DAP). This APB slave interface supports 32-bits
wide data, stalls, slave-generated aborts, and ten address bits [11:2] mapping 4KB of memory.
An extra PADDRDBG31 signal indicates to the processor the source of access.
Table A-12 on page A-17 shows the external debug interface signals.
11.10.2 Miscellaneous debug signals
This section describes the miscellaneous debug signals.
EDBGRQ
This signal generates a halting debug event, that is, it requests the processor to enter debug state.
When this occurs, the DSCR[5:2] method-of-debug entry bits are set to b0100. When
EDBGRQ is asserted, it must be held until DBGACK is asserted. Failure to do so leads to
Unpredictable behavior of the processor.
DBGACK
The processor asserts DBGACK to indicate that the system has entered debug state. It serves as
a handshake for the EDBGRQ signal. The DBGACK signal is also driven HIGH when the
debugger sets the DSCR[10] DbgAck bit to 1.
DBGNOPWRDWN
The processor asserts DBGNOPWRDWN when bit [0] of the Device Power down and Reset
Control Register is 1. The processor power controller must work in Emulate mode when this
signal is HIGH.
DBGROMADDR
The DBGROMADDR signal specifies bits [31:12] of the debug ROM physical address. This
is a configuration input and must be tied off or only change while the processor is in reset. In a
system with multiple debug ROMs, this address must be tied off to point to the top-level ROM
address.
DBGROMADDRV is the valid signal for DBGROMADDR. If the address cannot be
determined, DBGROMADDR must be tied off to zero and DBGROMADDRV must be tied
LOW. The value of these signals can be read from the Debug ROM Address Register (DRAR).