IWDG internal peripheral

Applicable for

STM32MP13x lines, STM32MP15x lines, STM32MP21x lines, STM32MP23x lines, STM32MP25x lines

1. Article purpose[edit | edit source]

The purpose of this article is to:

briefly introduce the IWDG peripheral and its main features,
indicate the peripheral instances assignment at boot time and their assignment at runtime (including whether instances can be allocated to secure contexts),
list the software frameworks and drivers managing the peripheral,
explain how to configure the peripheral.

2. Peripheral overview[edit | edit source]

The IWDG peripheral is a watchdog unit that can be used to protect application frameworks running on Cortex-A7 from endless loops. This peripheral supports an independent clocking source in order to be able to continue running even when the rest of the system is in low power mode (STOP, STANDBY). Another important feature of this block is the early interrupt feature that allows to trigger an interrupt at a given power supply threshold before reaching the final reset: this gives the opportunity to run a recovery mechanism that will try to revive the system with minimum impact.

Refer to the STM32 MPU reference manuals for the complete list of features, and to the software frameworks and drivers, introduced below, to see which features are implemented.

3. Peripheral usage[edit | edit source]

This chapter is applicable in the scope of the OpenSTLinux BSP running on the Arm^® Cortex^®-A processor(s), and the STM32CubeMPU Package running on the Arm^® Cortex^®-M processor.

3.1. Boot time assignment[edit | edit source]

Pay attention to the fact that IWDG can be configured to be automatically active at startup (without any software intervention) via BSEC. When this is the case, the watchdog is anyway frozen during ROM code execution but it will start to decrement its counter as soon as the ROM code is left so it is important to reload the watchdog from the boot chain in this case. This behavior is implemented for IWDG2 only in STMicroelectronics distribution.
Notice also that BSEC features some freeze bits that allow to freeze IWDG during platform Stop and Standby low power periods, avoiding to have to wake up (via RTC) for the only purpose of reloading the watchdog.

3.1.1. On STM32MP1 series[edit | edit source]

Click on to expand or collapse the legend...

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

⬚ means that the peripheral can be assigned to the given boot time context, but this configuration is not supported in STM32 MPU Embedded Software distribution.
☐ means that the peripheral can be assigned to the given boot time context.
☑ means that the peripheral is assigned by default to the given boot time context and that the peripheral is mandatory for the STM32 MPU Embedded Software distribution.
✓ is used for system peripherals that cannot be unchecked because they are hardware connected in the device.

The present chapter describes STMicroelectronics recommendations or choice of implementation. Additional possibilities might be described in STM32 MPU reference manuals.

Domain	Peripheral	Boot time allocation				Comment
Domain	Peripheral	Instance	Cortex-A7 secure (ROM code)	Cortex-A7 secure (TF-A BL2)	Cortex-A7 non-secure (U-Boot)	Comment
Core/Watchdog	IWDG	Any instance	✓	☐	☐

3.1.2. On STM32MP21x lines [edit | edit source]

Click on to expand or collapse the legend...

Check boxes illustrate the possible peripheral allocations supported by OpenSTLinux BSP:

⬚ means that the peripheral can be assigned to the given boot time context, but this configuration is not supported in OpenSTLinux BSP.
☐ means that the peripheral can be assigned to the given boot time context.
☑ means that the peripheral is assigned by default to the given boot time context and that the peripheral is mandatory for the OpenSTLinux BSP.
✓ is used for system peripherals that cannot be unchecked because they are hardware connected in the device.

The present chapter describes STMicroelectronics recommendations or choice of implementation. Additional possibilities might be described in STM32 MPU reference manuals.

Domain	Peripheral	Boot time allocation				Comment
Domain	Peripheral	Instance	Cortex-A35 secure (ROM code)	Cortex-A35 secure (TF-A BL2)	Cortex-A35 nonsecure (U-Boot)	Comment
Core/Watchdog	IWDG	IWDG1	✓	☑	☐
		IWDG2	✓	☐	☐
		IWDG3
		IWDG4

3.1.3. On STM32MP23x lines [edit | edit source]

Click on to expand or collapse the legend...

Check boxes illustrate the possible peripheral allocations supported by OpenSTLinux BSP:

⬚ means that the peripheral can be assigned to the given boot time context, but this configuration is not supported in OpenSTLinux BSP.
☐ means that the peripheral can be assigned to the given boot time context.
☑ means that the peripheral is assigned by default to the given boot time context and that the peripheral is mandatory for the OpenSTLinux BSP.
✓ is used for system peripherals that cannot be unchecked because they are hardware connected in the device.

The present chapter describes STMicroelectronics recommendations or choice of implementation. Additional possibilities might be described in STM32 MPU reference manuals.

Domain	Peripheral	Boot time allocation				Comment
Domain	Peripheral	Instance	Cortex-A35 secure (ROM code)	Cortex-A35 secure (TF-A BL2)	Cortex-A35 nonsecure (U-Boot)	Comment
Core/Watchdog	IWDG	IWDG1	✓	☑	☐
		IWDG2	✓	☐	☐
		IWDG3
		IWDG4

3.1.4. On STM32MP25x lines [edit | edit source]

Click on to expand or collapse the legend...

Check boxes illustrate the possible peripheral allocations supported by OpenSTLinux BSP:

⬚ means that the peripheral can be assigned to the given boot time context, but this configuration is not supported in OpenSTLinux BSP.
☐ means that the peripheral can be assigned to the given boot time context.
☑ means that the peripheral is assigned by default to the given boot time context and that the peripheral is mandatory for the OpenSTLinux BSP.
✓ is used for system peripherals that cannot be unchecked because they are hardware connected in the device.

The present chapter describes STMicroelectronics recommendations or choice of implementation. Additional possibilities might be described in STM32 MPU reference manuals.

Domain	Peripheral	Boot time allocation				Comment
Domain	Peripheral	Instance	Cortex-A35 secure (ROM code)	Cortex-A35 secure (TF-A BL2)	Cortex-A35 nonsecure (U-Boot)	Comment
Core/Watchdog	IWDG	IWDG1	✓	☑	☐
		IWDG2	✓	☐	☐
		IWDG3
		IWDG4
		IWDG5

3.2. Runtime assignment[edit | edit source]

IWDG1 can be allocated to the Cortex-A secure, which can export it to non-secure through SMC.
IWDG2 can be allocated to the Cortex-A non-secure. In this configuration, the secure monitor (from OP-TEE or TF-A) is able to receive IWDG early interrupts that can be used to save some logs before reset or, on STM32MP15x lines only, in a tentative to reset the Cortex-A7 without interfering with Cortex-M4 execution.

3.2.1. On STM32MP13x lines [edit | edit source]

Click on to expand or collapse the legend...

STM32MP13 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, but this configuration is not supported in STM32 MPU Embedded Software distribution.
☐ means that the peripheral can be assigned to the given runtime context.
☑ means that the peripheral is assigned by default to the given runtime context and that the peripheral is mandatory for the STM32 MPU Embedded Software distribution.
✓ is used for system peripherals that cannot be unchecked because they are hardware connected in the device.

Refer to How to assign an internal peripheral to an execution context for more information on how to assign peripherals manually or via STM32CubeMX.
The present chapter describes STMicroelectronics recommendations or choice of implementation. Additional possibilities might be described in STM32MP13 reference manuals.

Domain	Peripheral	Runtime allocation			Comment
Domain	Peripheral	Instance	Cortex-A7 secure (OP-TEE)	Cortex-A7 non-secure (Linux)	Comment
Core/Watchdog	IWDG	IWDG1	☑	☐
Core/Watchdog	IWDG	IWDG2	☐	☐	Shared (none or both): Cortex-A7 non secure for reload Cortex-A7 secure for early interrupt handling

3.2.2. On STM32MP15x lines [edit | edit source]

Click on to expand or collapse the legend...

STM32MP15 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, but this configuration is not supported in STM32 MPU Embedded Software distribution.
☐ means that the peripheral can be assigned to the given runtime context.
☑ means that the peripheral is assigned by default to the given runtime context and that the peripheral is mandatory for the STM32 MPU Embedded Software distribution.
✓ is used for system peripherals that cannot be unchecked because they are hardware connected in the device.

Refer to How to assign an internal peripheral to an execution 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
Core/Watchdog	IWDG	IWDG1	☐	☐
Core/Watchdog	IWDG	IWDG2	☐	☐		Shared (none or both): Cortex-A7 non secure for reload Cortex-A7 secure for early interrupt handling

3.2.3. On STM32MP21x lines [edit | edit source]

Click on to expand or collapse the legend...

STM32MP21 internal peripherals

Check boxes illustrate the possible peripheral allocations supported by OpenSTLinux BSP:

⬚ means that the peripheral can be assigned to the given runtime context, but this configuration is not supported in OpenSTLinux BSP.
☐ means that the peripheral can be assigned to the given runtime context.
☑ means that the peripheral is assigned by default to the given runtime context and that the peripheral is mandatory for the OpenSTLinux BSP.
✓ is used for system peripherals that cannot be unchecked because they are hardware connected in the device.

Refer to How to assign an internal peripheral to an execution context for more information on how to assign peripherals manually or via STM32CubeMX.
The present chapter describes STMicroelectronics recommendations or choice of implementation. Additional possibilities might be described in STM32MP21 reference manuals.

Domain	Peripheral	Runtime allocation					Comment
Domain	Peripheral	Instance	Cortex-A35 secure (OP-TEE / TF-A BL31)	Cortex-A35 nonsecure (Linux)	Cortex-M33 secure (TF-M)	Cortex-M33 nonsecure (STM32Cube)	Comment
Core/Watchdog	IWDG	IWDG1	☑^OP-TEE ☑^{TF-A BL31}	☐
		IWDG2	☐^OP-TEE ☐^{TF-A BL31}	☐
		IWDG3			☑	☐
		IWDG4			☐	☑

3.2.4. On STM32MP23x lines [edit | edit source]

Click on to expand or collapse the legend...

STM32MP23 internal peripherals

Check boxes illustrate the possible peripheral allocations supported by OpenSTLinux BSP:

⬚ means that the peripheral can be assigned to the given runtime context, but this configuration is not supported in OpenSTLinux BSP.
☐ means that the peripheral can be assigned to the given runtime context.
☑ means that the peripheral is assigned by default to the given runtime context and that the peripheral is mandatory for the OpenSTLinux BSP.
✓ is used for system peripherals that cannot be unchecked because they are hardware connected in the device.

Refer to How to assign an internal peripheral to an execution context for more information on how to assign peripherals manually or via STM32CubeMX.
The present chapter describes STMicroelectronics recommendations or choice of implementation. Additional possibilities might be described in STM32MP23 reference manuals.

Domain	Peripheral	Runtime allocation					Comment
Domain	Peripheral	Instance	Cortex-A35 secure (OP-TEE / TF-A BL31)	Cortex-A35 nonsecure (Linux)	Cortex-M33 secure (TF-M)	Cortex-M33 nonsecure (STM32Cube)	Comment
Core/Watchdog	IWDG	IWDG1	☑^OP-TEE ☑^{TF-A BL31}	☐
		IWDG2	☐^OP-TEE ☐^{TF-A BL31}	☐
		IWDG3			☑	☐
		IWDG4			☐	☑

3.2.5. On STM32MP25x lines [edit | edit source]

Click on to expand or collapse the legend...

STM32MP25 internal peripherals

Check boxes illustrate the possible peripheral allocations supported by OpenSTLinux BSP:

⬚ means that the peripheral can be assigned to the given runtime context, but this configuration is not supported in OpenSTLinux BSP.
☐ means that the peripheral can be assigned to the given runtime context.
☑ means that the peripheral is assigned by default to the given runtime context and that the peripheral is mandatory for the OpenSTLinux BSP.
✓ is used for system peripherals that cannot be unchecked because they are hardware connected in the device.

Refer to How to assign an internal peripheral to an execution context for more information on how to assign peripherals manually or via STM32CubeMX.
The present chapter describes STMicroelectronics recommendations or choice of implementation. Additional possibilities might be described in STM32MP25 reference manuals.

Domain	Peripheral	Runtime allocation						Comment
Domain	Peripheral	Instance	Cortex-A35 secure (OP-TEE / TF-A BL31)	Cortex-A35 nonsecure (Linux)	Cortex-M33 secure (TF-M)	Cortex-M33 nonsecure (STM32Cube)	Cortex-M0+ (STM32Cube)	Comment
Core/Watchdog	IWDG	IWDG1	☑^OP-TEE ☑^{TF-A BL31}	☐
		IWDG2	☐^OP-TEE ☐^{TF-A BL31}	☐
		IWDG3			☑	☐
		IWDG4			☐	☑
		IWDG5					☑

4. Software frameworks and drivers[edit | edit source]

Below are listed the software frameworks and drivers managing the IWDG peripheral for the embedded software components listed in the above tables.

OP-TEE: IWDG driver
Linux^®: Linux watchdog framework, ARM SMC watchdog driver and IWDG driver
TF-A: IWDG driver
U-Boot: ARM SMC watchdog driver

5. How to assign and configure the peripheral[edit | edit source]

The peripheral assignment can be done via the STM32CubeMX graphical tool (and manually completed if needed).
This tool also helps to configure the peripheral:

partial device trees (pin control and clock tree) generation for the OpenSTLinux software components,
HAL initialization code generation for the STM32CubeMPU Package.

The configuration is applied by the firmware running in the context in which the peripheral is assigned.