Debug support (DBG) RM0367
964/1043 RM0367 Rev 7
33.8 DWT (Data Watchpoint)
The Cortex
®
-M0+ DWT implementation provides two watchpoint register sets.
33.8.1 DWT functionality
The processor watchpoints implement both data address and PC based watchpoint
functionality, a PC sampling register, and support comparator address masking, as
described in the Armv6-M Arm
®
.
33.8.2 DWT Program Counter Sample Register
A processor that implements the data watchpoint unit also implements the Armv6-M
optional DWT Program Counter Sample Register (DWT_PCSR). This register permits a
debugger to periodically sample the PC without halting the processor. This provides coarse
grained profiling. See the Armv6-M Arm
®
for more information.
The Cortex
®
-M0+ DWT_PCSR records both instructions that pass their condition codes and
those that fail.
33.9 MCU debug component (DBG)
The MCU debug component helps the debugger provide support for:
• Low-power modes
• Clock control for timers, watchdog and I2C during a breakpoint
33.9.1 Debug support for low-power modes
To enter low-power mode, the instruction WFI or WFE must be executed.
The MCU implements several low-power modes which can either deactivate the CPU clock
or reduce the power of the CPU.
The core does not allow FCLK or HCLK to be turned off during a debug session. As these
are required for the debugger connection, during a debug, they must remain active. The
MCU integrates special means to allow the user to debug software in low-power modes.
For this, the debugger host must first set some debug configuration registers to change the
low-power mode behavior:
• In Sleep mode: FCLK and HCLK are still active. Consequently, this mode does not
impose any restrictions on the standard debug features.
• In Stop/Standby mode, the DBG_STOP bit must be previously set by the debugger.
This enables the internal RC oscillator clock to feed FCLK and HCLK in Stop mode.
When one of the DBG_STANDBY, DBG_STOP and DBG_SLEEP bit is set and the internal
reference voltage is stopped in low-power mode (ULP bit set in PWR_CR register), then the
Fast wakeup must be enabled (FWU bit set in PWR_CR).
For code example, refer to A.20.2: DBG debug in LPM code example.
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