DBGMCU internal peripheral

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1. Article purpose[edit source]

The purpose of this article is to:

briefly introduce the DBGMCU peripheral and its main features
indicate the level of security supported by this hardware block
explain how each instance can be allocated to the three runtime contexts and linked to the corresponding software components
explain, when necessary, how to configure the DBGMCU peripheral.

2. Peripheral overview[edit source]

The DBGMCU peripheral is used to configure internal peripherals behavior when one of the cores (Cortex^®-A7 or Cortex^®-M4) enters in debug mode.
For instance, it allows to freeze a watchdog (IWDG) to avoid getting a watchdog reset when the Cortex^®-A7 enters in debug mode (via a breakpoint or JTAG break).

2.1. Features[edit source]

Refer to the STM32MP15 reference manuals for the complete list of features, and to the software components, introduced below, to see which features are implemented.

2.2. Security support[edit source]

The DBGMCU is a non secure peripheral.

3. Peripheral usage and associated software[edit source]

3.1. Boot time[edit source]

DBGMCU is partly initialized by the FSBL at boot time in order to freeze IWDG2 when the Cortex^®-A7 enters in debug mode.

3.2. Runtime[edit source]

3.2.1. Overview[edit source]

There is no real runtime support for DBGMCU. Instead, users who need to freeze some peripherals for a debug session should complete the minimal initialization done in the FSBL with their needs.

3.2.2. Software frameworks[edit source]

Domain	Peripheral	Software components			Comment
Domain	Peripheral	OP-TEE	Linux	STM32Cube	Comment
Trace & Debug	DBGMCU

3.2.3. Peripheral configuration[edit source]

The configuration is applied by the firmware running in the context to which the peripheral is assigned. The configuration can be done alone via the STM32CubeMX tool for all internal peripherals, and then manually completed (particularly for external peripherals), according to the information given in the corresponding software framework article.

3.2.4. Peripheral assignment[edit source]

Internal peripherals

Check boxes illustrate the possible peripheral allocations supported by STM32 MPU Embedded Software:

☐ means that the peripheral can be assigned (☑) to the given runtime context.
✓ is used for system peripherals that cannot be unchecked because they are statically connected in the device.

Refer to How to assign an internal peripheral to a runtime context for more information on how to assign peripherals manually or via STM32CubeMX.
The present chapter describes STMicroelectronics recommendations or choice of implementation. Additional possiblities might be described in STM32MP15 reference manuals.

Domain	Peripheral	Runtime allocation				Comment
Domain	Peripheral	Instance	Cortex-A7 secure (OP-TEE)	Cortex-A7 non-secure (Linux)	Cortex-M4 (STM32Cube)	Comment
Trace & Debug	DBGMCU	DBGMCU				No assignment