1. Article purpose[edit | edit source]
The purpose of this article is to:
- briefly introduce the LPUART 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 LPUART peripheral is similar to the UART, with minimum power consumption.
High-speed data communications can be achieved by using the HPDMA or LPDMA for multibuffer configuration.
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]
3.1. Boot time assignment[edit | edit source]
3.1.1. On STM32MP2 series[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
| |||
|---|---|---|---|---|---|---|
| Instance | Cortex-A35 secure (ROM code) |
Cortex-A35 secure (TF-A BL2) |
Cortex-A35 nonsecure (U-Boot) | |||
| Low speed interface | LPUART | LPUART1 | ⬚ | ⬚ | ||
3.2. Runtime assignment[edit | edit source]
3.2.1. 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 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
| ||||
|---|---|---|---|---|---|---|---|
| Instance | Cortex-A35 secure (OP-TEE / TF-A BL31) |
Cortex-A35 nonsecure (Linux) |
Cortex-M33 secure (TF-M) |
Cortex-M33 nonsecure (STM32Cube) | |||
| Low speed interface | LPUART | LPUART1 | ⬚OP-TEE ⬚TF-A BL31 |
⬚ | ☐ | ☐ | |
3.2.2. 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 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
| ||||
|---|---|---|---|---|---|---|---|
| Instance | Cortex-A35 secure (OP-TEE / TF-A BL31) |
Cortex-A35 nonsecure (Linux) |
Cortex-M33 secure (TF-M) |
Cortex-M33 nonsecure (STM32Cube) | |||
| Low speed interface | LPUART | LPUART1 | ⬚OP-TEE ⬚TF-A BL31 |
⬚ | ☐ | ☐ | |
3.2.3. 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 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
| |||||
|---|---|---|---|---|---|---|---|---|
| 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) | |||
| Low speed interface | LPUART | LPUART1 | ⬚OP-TEE ⬚TF-A BL31 |
⬚ | ☐ | ☐ | ☐ | |
4. Software frameworks and drivers[edit | edit source]
The STM32MP2 series devices feature a LPUART instance supporting only Asynchronous mode.
Below are listed the software frameworks and drivers managing the LPUART peripheral for the embedded software components listed in the above tables.
- Linux®: serial/tty framework
- STM32Cube: LPUART HAL driver and header file of LPUART HAL module
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.
See also additional information in the Serial TTY device tree configuration article for Linux®.
Arm® is a registered trademark of Arm Limited (or its subsidiaries) in the US and/or elsewhere. 