1. Article purpose[edit | edit source]
The purpose of this article is to:
- briefly introduce the LTDC 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 LCD-TFT (Liquid Crystal Display - Thin Film Transistor) Display Controller peripheral (LTDC) is used to provide an interface to a variety of parallel digital RGB LCD and TFT display panels. The LTDC generates the parallel digital RGB (Red, Green, Blue) signals and the related control signals (horizontal and vertical synchronizations, Pixel Clock and Data Enable).
Moreover, on STM32MP15x lines , the LTDC is connected to the DSI internal peripheral that provides an interface to communicate with MIPI® DSI-compliant display panels.
On STM32MP13x lines , the LTDC layer2 can be set as secure (under ETZPC control), whereas the layer1 is always non-secure. On STM32MP15x lines , the LTDC is a non-secure peripheral.
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 STM32MP1 Series[edit | edit source]
The LTDC is used at boot time for displaying a splash screen thanks to the U-Boot framework [1].
Click on the right to expand 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 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 statically 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-A7 secure (ROM code) |
Cortex-A7 secure (TF-A BL2) |
Cortex-A7 non-secure (U-Boot) | |||
Visual | LTDC | LTDC | ☐ |
3.2. Runtime assignment[edit | edit source]
3.2.1. On STM32MP13x lines [edit | edit source]
Click on the right to expand 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 runtime context.
- ⬚ 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 statically 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) | |||
Visual | LTDC | LTDC | ☐ | ☐ | Shareable (multiple choices supported) |
3.2.2. On STM32MP15x lines [edit | edit source]
Click on the right to expand 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 runtime context.
- ⬚ 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 statically 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) | |||
Visual | LTDC | LTDC | ☐ |
4. Software frameworks and drivers[edit | edit source]
Below are listed the software frameworks and drivers managing the LTDC peripheral for the embedded software components listed in the above tables.
- Linux®: DRM/KMS framework
- OP-TEE: OP-TEE framework (for the trusted UI)
- U-Boot: U-Boot framework (for the display splash screen)
On STM32MP13x lines , the LTDC can be set secure from ETZPC : this is done at runtime when OP-TEE trusted user interface (Trusted UI) is launched in order to switch the LTDC control and the input layer2 as secure, to display a secure content that cannot be seen from the non-secure world.
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 LTDC device tree configuration article for Linux®.
6. How to go further[edit | edit source]
Refer to STM32 LTDC application note (AN4861) [2] for a detailed description of the LTDC peripheral and applicable use-cases.
Even if this application note is related to STM32 microcontrollers, it also applies to STM32 MPUs.
7. References[edit | edit source]