CEC internal peripheral

Applicable for

STM32MP15x lines

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1. Article purpose

The purpose of this article is to:

• briefly introduce the CEC 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

The CEC (consumer electronics control) or HDMI-CEC peripheral is used to receive/send messages from/to devices, such as TV or tuner, through a HDMI cable.

Refer to the STM32MP15 reference manuals for the complete list of features, and to the software frameworks and drivers, introduced below, to see which features are implemented.

Refer to the STM32 CEC presentation for an overview of the CEC hardware block capabilities.

3. Peripheral usage

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

The CEC peripheral is not used at boot time.

3.2. Runtime assignment

3.2.1. On STM32MP15x lines 

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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, but this configuration is not supported in STM32 MPU Embedded Software distribution.
• ☐ 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.
• ✓ 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)
Visual	CEC	CEC		☐	☐	Assignment (single choice)

4. Software frameworks and drivers

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

• Linux^®: CEC framework
• STM32Cube: STM32Cube CEC HAL driver and header file of CEC HAL module

5. How to assign and configure the peripheral

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 CEC device tree configuration article for Linux^®.

6. How to go further

Refer to the STM32 CEC application note (AN4066) for a detailed description of the CEC peripheral and applicable use-cases.

Even if this application note is related to STM32 microcontrollers, it also applies to STM32 MPUs.