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13.6
External debug interface
DSCR
DBGEN
[15:14]
0
XX
1
00
1
00
1
00
1
00
1
00
ARM DDI 0301H
ID012310
The debug architecture provides two control signals called SPIDEN and SPNIDEN. that are
part of the external debug interface.
The Secure Privileged Invasive Debug Enable input pin, SPIDEN, that enables
SPIDEN
and disables invasive debug in the Secure world:
•
If this input signal is HIGH, invasive debug is permitted in all Secure
modes. In this case invasive debug is permitted in Secure User mode,
regardless value of SUIDEN bit.
•
If this input signal is LOW, invasive debug is not permitted in any Secure
privileged mode. Invasive debug is permitted in Secure User mode
according to the SUIDEN bit.
The Secure Privileged Non-Invasive Debug Enable input pin, SPNIDEN, that
SPNIDEN
enables and disables non-invasive debug in the Secure world:
•
If this input signal is HIGH, non-invasive debug is permitted in all Secure
modes. In this case non-invasive debug is permitted in Secure User mode,
regardless of the value of the SUNIDEN bit.
•
If this input signal is LOW, non-invasive debug is not permitted in all
Secure privileged modes. Non-invasive debug is permitted in Secure User
mode according to the SUNIDEN bit.
Note
You must control access to the SPIDEN and SPNIDEN pins, as they represent a
•
significant security risk. For example, it must not be possible to set these pins through the
boundary scan in a final device.
For software systems that do not use any TrustZone security features, the SPIDEN and
•
SPNIDEN pins must be driven HIGH to enable debug by default.
Table 13-21 lists the relationship between the DBGEN input pin, the SPIDEN input pin, the
SUIDEN control bit, the NS bit, the processor mode and the debug capabilities.
SPIDEN
SUIDEN
X
X
1
X
0
0
0
0
0
0
0
1
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NS
Mode
Debug-mode
bit
X
X
Debug disabled.
X
X
No debug mode
selected
1
not Secure
No debug mode
Monitor
selected
X
Secure
Debug not
Monitor
permitted
0
X
Debug not
permitted
1
not Secure
No debug mode
Monitor
selected
Table 13-21 Secure debug behavior
Notes
DSCR[15:14] reads as zero
Permitted in Non-secure
a
state and in all modes in
Secure state.
Permitted only in
a
Non-secure state.
Not permitted in Secure
b
state.
Not permitted in Secure
b
state.
Permitted in Non-secure
a
state.
Debug
13-28
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