AN4989 datasheet(40/99 Pages) STMICROELECTRONICS

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Connecting to the board

AN4989

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DocID030181 Rev 2

4.3

Low-power case

By default, the debug connection is lost if the application puts the MCU in Sleep, Stop, or

Standby mode while the debug features are used. This is due to the fact that the Cortex®-M

core is not clocked in any of these modes.

However, the setting of dedicated configuration bits in the DBGMCU_CR register allows

software debug even when the low-power modes are used extensively.

Refer to the PWR and DBG sections of the reference manual for details.

Appendix A: Managing DBGMCU registers on page 78 guides the user through the various

means to manage DBGMCU depending on IDE and needs.

Caution:

In order to reduce power consumption, some applications turn all GPIOs to analog input

mode, including SWD GPIOs. This is the case for all PWR examples provided in

STM32Cube (debug connection is lost after SystemPower_Config() which sets all

GPIOs in Analog Input State).

Enabling low-power debug degrades power consumption performance by keeping some

clocks enabled and by preventing to optimize GPIO state. Even if this is useful for functional

debugging, it has anyhow to be banned as soon as the target is to measure/enhance power

consumption.

All DBGMCU registers values are kept while reset. Users must pay attention not to let

debug or unwanted states when returning to normal execution (refer to Section 9: From

debug to release on page 76).

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