Last edited 2 months ago

IWDG internal peripheral

Applicable for STM32MP13x lines, STM32MP15x lines, STM32MP25x lines

1. Article purpose[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 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 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 source]

3.1.1. On STM32MP1 series[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.

Click on How to.png 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.
  • 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.
  • 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.
  • 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 How to.png
Instance Cortex-A7
secure
(ROM code)
Cortex-A7
secure
(TF-A BL2)
Cortex-A7
non-secure
(U-Boot)
Core/Watchdog IWDG Any instance

3.1.2. On STM32MP2 series[edit source]

Click on How to.png to expand or collapse the legend...

  • 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.
  • 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.
  • 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 STM32MP25 reference manuals.

Domain Peripheral Boot time allocation Comment How to.png
Instance Cortex-A35
secure
(ROM code)
Cortex-A35
secure
(TF-A BL2)
Cortex-A35
non-secure
(U-Boot)
Core/Watchdog IWDG IWDG1
IWDG2
IWDG3
IWDG4
IWDG5

3.2. Runtime assignment[edit source]

3.2.1. On STM32MP13x lines More info.png[edit source]

Click on How to.png 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.
  • 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.
  • means that the peripheral can be assigned to the given runtime context, but this configuration is not supported in 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 How to.png
Instance Cortex-A7
secure
(OP-TEE)
Cortex-A7
non-secure
(Linux)
Core/Watchdog IWDG IWDG1 IWDG1 is secure programmable via ETZPC but this is not used / supported so not shown in STM32CubeMX
IWDG2 Shared (none or both):
  • Cortex-A7 non secure for reload
  • Cortex-A7 secure for early interrupt handling

3.2.2. On STM32MP15x lines More info.png[edit source]

Click on How to.png 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.
  • 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.
  • means that the peripheral can be assigned to the given runtime context, but this configuration is not supported in 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 How to.png
Instance Cortex-A7
secure
(OP-TEE)
Cortex-A7
non-secure
(Linux)
Cortex-M4

(STM32Cube)
Core/Watchdog IWDG IWDG1
IWDG2 Shared (none or both):
  • Cortex-A7 non secure for reload
  • Cortex-A7 secure for early interrupt handling

3.2.3. On STM32MP25x lines More info.png[edit source]

Click on How to.png to expand or collapse the legend...

STM32MP25 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.
  • 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.
  • means that the peripheral can be assigned to the given runtime context, but this configuration is not supported in 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 STM32MP25 reference manuals.

Domain Peripheral Runtime allocation Comment How to.png
Instance Cortex-A35
secure
(OP-TEE /
TF-A BL31)
Cortex-A35
non-secure
(Linux)
Cortex-M33
secure
(TF-M)
Cortex-M33
non-secure
(STM32Cube)
Cortex-M0+
Warning.png
(STM32Cube)
Core/Watchdog IWDG IWDG1 OP-TEE
TF-A BL31
IWDG2 OP-TEE
TF-A BL31
IWDG3
IWDG4
IWDG5

4. Software frameworks and drivers[edit source]

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

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 More info.png only, in a tentative to reset the Cortex-A7 without interfering with Cortex-M4 execution.

5. How to assign and configure the peripheral[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.