LPTIM internal peripheral

Applicable for STM32MP13x lines, STM32MP15x lines

1 Article purpose[edit]

The purpose of this article is to:

  • briefly introduce the LPTIM 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]

The LPTIM peripheral is a single channel low-power timer unit, that can continue to run even during low power modes when it selects a clock source that remains active in RCC.

The LPTIM peripheral is available in different configurations. Depending on the selected instance, it can act as PWM, quadrature encoder[1], external event counter or trigger source for other internal peripherals, like ADC[2], DFSDM[3] and DAC[4] (on STM32MP15x lines More info.png).

LPTIM features PWM External event counter
Trigger source
Quadrature encoder
LPTIM1, LPTIM2 Yes Yes Yes
LPTIM3 Yes Yes
LPTIM4, LPTIM5 Yes
  • On STM32MP13x lines More info.png, LPTIM3 can be used for RCC HSE clock source monitoring

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]

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]

The LPTIM peripheral is not used at boot time.

3.2 Runtime assignment[edit]

3.2.1 On STM32MP13x lines More info.png[edit]

Click on the right to expand 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
Instance Cortex-A7
secure
(OP-TEE)
Cortex-A7
non-secure
(Linux)
Core/Timers LPTIM LPTIM1
LPTIM2 Assignment (single choice)
LPTIM3 Assignment (single choice)
LPTIM3 can be used for HSE monitoring
LPTIM4
LPTIM5

3.2.2 On STM32MP15x lines More info.png[edit]

Click on the right to expand 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
Instance Cortex-A7
secure
(OP-TEE)
Cortex-A7
non-secure
(Linux)
Cortex-M4

(STM32Cube)
Core/Timers LPTIM LPTIM1 Assignment (single choice)
LPTIM2 Assignment (single choice)
LPTIM3 Assignment (single choice)
LPTIM4 Assignment (single choice)
LPTIM5 Assignment (single choice)

4 Software frameworks and drivers[edit]

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

5 How to assign and configure the peripheral[edit]

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.

For Linux kernel configuration, please refer to LPTIM device tree configuration and STM32 LPTIM Linux driver articles.

6 References[edit]