1. Article purpose[edit | edit source]
The purpose of this article is to:
- briefly introduce the LPDMA 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 LPDMA peripheral is used to perform high-speed data transfers between internal memory and internal memory or between peripherals and internal memory. The LPDMA controller offers 4 channels. The selection of the device connected to each channel and controlling DMA transfers is done in LPDMA peripheral.
The LPDMA is a secure peripheral. This means that it performs each transfer in the context of the master that requested it:
- a transfer requested by the Arm® Cortex®-A35 or Arm® Cortex®-M33 non-secure core propagates non-secure accesses to the targeted device and/or internal memory.
- a transfer requested by the Arm® Cortex®-A35 or Arm® Cortex®-M33 secure core propagates secure accesses to the targeted device and/or internal memory.
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]
3.1.1. On STM32MP25x lines 
[edit | edit source]
Click on 
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 Yocto-based OpenSTLinux Embedded Software.
- ⬚ means that the peripheral can be assigned to the given boot time context, but this configuration is not supported in Yocto-based OpenSTLinux Embedded Software.
- ✓ 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) | |||
| Core/DMA | LPDMA 
|
LPDMA1 | ☐ | ☐ | ☐ | Shareable at internal peripheral level thanks to the RIF: see the boot time allocation per feature |
The below table shows the possible boot time allocations for the features of the LPDMA1 instance.
| Feature | Boot time allocation
|
Comment | ||
|---|---|---|---|---|
| Cortex-A35 secure (ROM code) |
Cortex-A35 secure (TF-A BL2) |
Cortex-A35 nonsecure (U-Boot) | ||
| LPDMA1 channel y | ⬚ | ⬚ | ||
3.2. Runtime assignment[edit | edit source]
3.2.1. On STM32MP25x lines [edit | edit source]
Click on to expand or collapse the legend...
Check boxes illustrate the possible peripheral allocations supported by Yocto-based OpenSTLinux 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 Yocto-based OpenSTLinux Embedded Software.
- ⬚ means that the peripheral can be assigned to the given runtime context, but this configuration is not supported in Yocto-based OpenSTLinux Embedded Software.
- ✓ 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) | |||
| Core/DMA | LPDMA
|
LPDMA | ☐OP-TEE | ☐ | ☐ | ☐ | ☐ | Shareable at internal peripheral level thanks to the RIF: see the runtime allocation per feature |
The below table shows the possible runtime allocations for the features of the LPDMA1 instance.
| Feature | Runtime allocation
|
Comment | ||||
|---|---|---|---|---|---|---|
| Cortex-A35 secure (OP-TEE / TF-A BL31) |
Cortex-A35 nonsecure (Linux) |
Cortex-M33 secure (TF-M) |
Cortex-M33 nonsecure (STM32Cube) |
Cortex-M0+ (STM32Cube) | ||
| LPDMA1 channel y | ⬚OP-TEE | ⬚ | ⬚ | ☐ | ☐ | |
4. Software frameworks and drivers[edit | edit source]
Below are listed the software frameworks and drivers managing the LPDMA peripheral for the embedded software components listed in the above tables.
- Linux®: dmaengine framework
- STM32Cube: DMA HAL driver and header file of DMA HAL module
STM32CubeMX allows to distinguish between non-secure and secure channels, among all the available channels.
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 by generating:
- partial device trees (pin control and clock tree) for the OpenSTLinux software components,
- HAL initialization code for the STM32CubeMPU Package.
The configuration is applied by the firmware running in the context in which the peripheral is assigned.
6. References[edit | edit source]
Arm® is a registered trademark of Arm Limited (or its subsidiaries) in the US and/or elsewhere. 
Arm® is a registered trademark of Arm Limited (or its subsidiaries) in the US and/or elsewhere.