The debug and trace system offers a flexible and powerful mechanism for non-intrusive debugging.
An external debugger can access the device via the DAP.
The debug access port (DAP) implements a standard ARM® CoreSight™ serial wire debug port (SW-DP), which implements the serial wire debug protocol (SWD). SWD is a two-pin serial interface, see SWDCLK and SWDIO in Debug and trace overview.
In addition to the default access port in CPU (AHB-AP), the DAP includes a custom control access port (CTRL-AP). The CTRL-AP is described in more detail in CTRL-AP - Control access port.
Access port protection blocks the debugger from read and write access to all CPU registers and memory-mapped addresses when enabled.
Access port protection is enabled and disabled differently depending on the build code of the device.
This information refers to build codes Dxx and earlier.
By default, access port protection is disabled.
Access port protection is enabled by writing UICR.APPROTECT to Enabled
and performing
any reset. See Reset for more information.
Access port protection is disabled by issuing an ERASEALL command via CTRL-AP. This command will erase the flash,
UICR, and RAM, including UICR.APPROTECT. Erasing UICR will
set UICR.APPROTECT value to Disabled
. CTRL-AP is described in more detail in CTRL-AP - Control access port.
This information refers to build codes Fxx and later.
By default, access port protection is enabled.
Access port protection is disabled by issuing an ERASEALL command via CTRL-AP. Read CTRL-AP.APPROTECTSTATUS to ensure that access port protection is disabled, and repeat the ERASEALL command if needed. This command will erase the flash, UICR, and RAM. CTRL-AP is described in more detail in CTRL-AP - Control access port. Access port protection will remain disabled until one of the following occurs:
To keep access port protection disabled, the following actions must be performed:
HwDisabled
. This disables the hardware part of the access port protection
scheme after the first reset of any type. The hardware part of the access port protection
will stay disabled as long as UICR.APPROTECT is not overwritten.SwDisable
. This disables the software part of the access port
protection scheme.Access port protection is enabled when the disabling conditions are not present. For
additional security, it is recommended to write Enabled
to UICR.APPROTECT, and have firmware write
Force
to APPROTECT.FORCEPROTECT. This is illustrated in the following figure.
Base address | Peripheral | Instance | Description | Configuration | |
---|---|---|---|---|---|
0x40000000 | APPROTECT | APPROTECT |
APPROTECT control |
Register | Offset | Description | |
---|---|---|---|
FORCEPROTECT | 0x550 |
Software force enable APPROTECT mechanism until next reset. |
|
DISABLE | 0x558 |
Software disable APPROTECT mechanism |
Address offset: 0x550
Software force enable APPROTECT mechanism until next reset.
Bit number | 31 | 30 | 29 | 28 | 27 | 26 | 25 | 24 | 23 | 22 | 21 | 20 | 19 | 18 | 17 | 16 | 15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | |||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
ID | A | A | A | A | A | A | A | A | |||||||||||||||||||||||||||
Reset 0xFFFFFFFF | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | |||
ID | Access | Field | Value ID | Value | Description | ||||||||||||||||||||||||||||||
A | RW1 |
FORCEPROTECT |
Write 0x0 to force enable APPROTECT mechanism |
||||||||||||||||||||||||||||||||
Force |
0x0 |
Software force enable APPROTECT mechanism |
Address offset: 0x558
Software disable APPROTECT mechanism
Bit number | 31 | 30 | 29 | 28 | 27 | 26 | 25 | 24 | 23 | 22 | 21 | 20 | 19 | 18 | 17 | 16 | 15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | |||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
ID | A | A | A | A | A | A | A | A | |||||||||||||||||||||||||||
Reset 0x00000000 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | |||
ID | Access | Field | Value ID | Value | Description | ||||||||||||||||||||||||||||||
A | RW |
DISABLE |
Software disable APPROTECT mechanism |
||||||||||||||||||||||||||||||||
SwDisable |
0x5A |
Software disable APPROTECT mechanism |
The control access port (CTRL-AP) is a custom access port that enables control of the device when other access ports in the DAP are disabled by the access port protection.
Access port protection is described in more detail in Access port protection.
Control access port has the following features:
Register | Offset | Description | |
---|---|---|---|
RESET | 0x000 |
Soft reset triggered through CTRL-AP |
|
ERASEALL | 0x004 |
Erase all |
|
ERASEALLSTATUS | 0x008 |
Status register for the ERASEALL operation |
|
APPROTECTSTATUS | 0x00C |
Status register for access port protection |
|
IDR | 0x0FC |
CTRL-AP identification register, IDR |
Address offset: 0x000
Soft reset triggered through CTRL-AP
Bit number | 31 | 30 | 29 | 28 | 27 | 26 | 25 | 24 | 23 | 22 | 21 | 20 | 19 | 18 | 17 | 16 | 15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | |||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
ID | A | ||||||||||||||||||||||||||||||||||
Reset 0x00000000 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | |||
ID | Access | Field | Value ID | Value | Description | ||||||||||||||||||||||||||||||
A | RW |
RESET |
Soft reset triggered through CTRL-AP. See Reset behavior in POWER chapter for more details. |
||||||||||||||||||||||||||||||||
NoReset |
0 |
Reset is not active |
|||||||||||||||||||||||||||||||||
Reset |
1 |
Reset is active. Device is held in reset. |
Address offset: 0x004
Erase all
Bit number | 31 | 30 | 29 | 28 | 27 | 26 | 25 | 24 | 23 | 22 | 21 | 20 | 19 | 18 | 17 | 16 | 15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | |||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
ID | A | ||||||||||||||||||||||||||||||||||
Reset 0x00000000 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | |||
ID | Access | Field | Value ID | Value | Description | ||||||||||||||||||||||||||||||
A | W |
ERASEALL |
Erase all flash and RAM |
||||||||||||||||||||||||||||||||
NoOperation |
0 |
No operation |
|||||||||||||||||||||||||||||||||
Erase |
1 |
Erase all flash and RAM |
Address offset: 0x008
Status register for the ERASEALL operation
Bit number | 31 | 30 | 29 | 28 | 27 | 26 | 25 | 24 | 23 | 22 | 21 | 20 | 19 | 18 | 17 | 16 | 15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | |||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
ID | A | ||||||||||||||||||||||||||||||||||
Reset 0x00000000 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | |||
ID | Access | Field | Value ID | Value | Description | ||||||||||||||||||||||||||||||
A | R |
ERASEALLSTATUS |
Status register for the ERASEALL operation |
||||||||||||||||||||||||||||||||
Ready |
0 |
ERASEALL is ready |
|||||||||||||||||||||||||||||||||
Busy |
1 |
ERASEALL is busy (on-going) |
Address offset: 0x00C
Status register for access port protection
Bit number | 31 | 30 | 29 | 28 | 27 | 26 | 25 | 24 | 23 | 22 | 21 | 20 | 19 | 18 | 17 | 16 | 15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | |||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
ID | A | ||||||||||||||||||||||||||||||||||
Reset 0x00000000 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | |||
ID | Access | Field | Value ID | Value | Description | ||||||||||||||||||||||||||||||
A | R |
APPROTECTSTATUS |
Status register for access port protection |
||||||||||||||||||||||||||||||||
Enabled |
0 |
Access port protection enabled |
|||||||||||||||||||||||||||||||||
Disabled |
1 |
Access port protection not enabled |
Address offset: 0x0FC
CTRL-AP identification register, IDR
Bit number | 31 | 30 | 29 | 28 | 27 | 26 | 25 | 24 | 23 | 22 | 21 | 20 | 19 | 18 | 17 | 16 | 15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | |||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
ID | E | E | E | E | D | D | D | D | C | C | C | C | C | C | C | B | B | B | B | A | A | A | A | A | A | A | A | ||||||||
Reset 0x02880000 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 1 | 0 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | |||
ID | Access | Field | Value ID | Value | Description | ||||||||||||||||||||||||||||||
A | R |
APID |
AP identification |
||||||||||||||||||||||||||||||||
B | R |
CLASS |
Access port (AP) class |
||||||||||||||||||||||||||||||||
NotDefined |
0x0 |
No defined class |
|||||||||||||||||||||||||||||||||
MEMAP |
0x8 |
Memory access port |
|||||||||||||||||||||||||||||||||
C | R |
JEP106ID |
JEDEC JEP106 identity code |
||||||||||||||||||||||||||||||||
D | R |
JEP106CONT |
JEDEC JEP106 continuation code |
||||||||||||||||||||||||||||||||
E | R |
REVISION |
Revision |
Symbol | Description | Min. | Typ. | Max. | Units | ||||
---|---|---|---|---|---|---|---|---|---|
Rpull |
Internal SWDIO and SWDCLK pull up/down resistance |
13 | kΩ | ||||||
fSWDCLK |
SWDCLK frequency |
0.125 | 8 | MHz |
Before an external debugger can access either CPU's access port (AHB-AP) or the control access port (CTRL-AP), the debugger must first request the device to power up via CxxxPWRUPREQ in the SWJ-DP.
If the device is in System OFF when power is requested via CxxxPWRUPREQ, the system will wake up and the DIF flag in RESETREAS will be set. The device is in the Debug Interface mode as long as the debugger is requesting power via CxxxPWRUPREQ. Once the debugger stops requesting power via CxxxPWRUPREQ, the device is back in normal mode. Some peripherals behave differently in Debug Interface mode compared to normal mode. These differences are described in more detail in the chapters of the peripherals that are affected.
When a debug session is over, the external debugger must make sure to put the device back into normal mode since the overall power consumption is higher in Debug Interface mode than in normal mode.
For details on how to use the debug capabilities, read the debug documentation of your IDE.
The nRF52840 supports real-time debugging.
Real-time debugging allows interrupts to execute to completion in real time when breakpoints are set in Thread mode or lower priority interrupts. This enables developers to set breakpoints and single-step through the code without the risk of real-time event-driven threads running at higher priority failing. For example, this enables the device to continue to service the high-priority interrupts of an external controller or sensor without failure or loss of state synchronization while the developer steps through code in a low-priority thread.
The device supports ETM and ITM trace.
Trace data from the ETM and the ITM is sent to an external debugger via a 4-bit wide parallel trace port interface unit (TPIU), see TRACEDATA[0] through TRACEDATA[3] and TRACECLK in Debug and trace overview.
In addition to parallel trace, the TPIU supports serial trace via the serial wire output (SWO) trace protocol. Parallel and serial trace cannot be used at the same time. ETM trace is only supported in Parallel Trace mode, while ITM trace is supported in both Parallel and Serial Trace modes.
For details on how to use the trace capabilities, read the debug documentation of your IDE.
TPIU's trace pins are multiplexed with GPIOs. SWO and TRACEDATA[0] use the same GPIO. See Pin assignments for more information.
Trace speed is configured in register TRACECONFIG. The speed of the trace pins depends on the DRIVE setting of the GPIOs that the trace pins are multiplexed with. Only S0S1 and H0H1 drives are suitable for debugging. S0S1 is the default DRIVE setting at reset. If parallel or serial trace port signals are not fast enough with the default settings, all GPIOs in use for tracing should be set to high drive (H0H1). The DRIVE setting for these GPIOs should not be overwritten by firmware during the debugging session.
Symbol | Description | Min. | Typ. | Max. | Units | ||||
---|---|---|---|---|---|---|---|---|---|
Tcyc |
Clock period as defined by Arm in the Timing specifications for Trace Port Physical Interface of the Embedded Trace Macrocell Architecture Specification |
62.5 | 500 | ns |