STM32MP2 ADC internal peripheral

Applicable for

STM32MP23x lines  STM32MP25x lines

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1. Article purpose

The purpose of this article is to:

• briefly introduce the ADC 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 ADC peripheral is a successive approximation analog-to-digital converter.

On STM32MP2 series, there are up to three physical ADCs distributed between two ADC blocks:

• Each ADC has up to 20 multiplexed channels.

SoC	ADCs	External channels	Internal channels
STM32MP21x lines	ADC1	18	2
	ADC2	14	5
STM32MP23x lines	ADC1	18	2
	ADC2	14	6
	ADC3	14	6
STM32MP25x lines	ADC1	18	2
	ADC2	14	6
	ADC3	14	6

Information

ADC1 and ADC2 are tightly coupled on STM32MP23x lines  and STM32MP25x lines  but ADC3 is controlled independently.

• Configurable resolution: 12, 10, 8, 6 bits.
• The conversions can be performed in single, continuous, scan, or discontinuous mode.
• The result can be read in a left-aligned or right-aligned 32-bit data register by using CPU or DMA.
• The analog watchdog feature allows the application to detect if the input voltage goes beyond the user-defined high or low thresholds.
• The ADC clock source used for conversions is selected by the RCC independently from the AHB bus clock that is used to access the ADC registers.
• The common reference voltage can be provided by either VREFBUF or any other external regulator wired to VREF+ pin.

Each ADC supports two contexts to manage conversions:

• Regular conversions can be done in sequence, running in the background.
• Injected conversions have a higher priority, and so can interrupt the regular sequence (either triggered in software or hardware). The regular sequence is resumed in case it has been interrupted.
• Each context has its own configurable sequence and trigger: software, TIM, LPTIM, and EXTI.

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

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

3.1.1. On STM32MP21x lines 

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• ☐ 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)
Analog	ADC	ADC1		⬚	☐
		ADC2		⬚	☐

3.1.2. On STM32MP23x lines 

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)
Analog	ADC	ADC12		⬚	☐
		ADC3		⬚	☐

3.1.3. On STM32MP25x lines 

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)
Analog	ADC	ADC12		⬚	☐
		ADC3		⬚	☐

3.2. Runtime assignment

3.2.1. On STM32MP21x lines 

Click on to expand or collapse the legend...

STM32MP21 internal peripherals

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 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)
Analog	ADC	ADC1	☐OP-TEE	☐	⬚	☐
		ADC2	☐OP-TEE	☐	⬚	☐

3.2.2. On STM32MP23x lines 

Click on to expand or collapse the legend...

STM32MP23 internal peripherals

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 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)
Analog	ADC	ADC12	☐OP-TEE	☐	⬚	☐
		ADC3	☐OP-TEE	☐	⬚	☑	ADC3 may be used by the UCSI firmware to measure the Vbus level on the Type-C connector.

3.2.3. On STM32MP25x lines 

Click on to expand or collapse the legend...

STM32MP25 internal peripherals

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)
Analog	ADC	ADC12	☐OP-TEE	☐	⬚	☐
		ADC3	☐OP-TEE	☐	⬚	☑		ADC3 may be used by the UCSI firmware to measure the Vbus level on the Type-C connector.

4. Software frameworks and drivers

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

• Linux^®: IIO framework
• OP-TEE: OP-TEE ADC driver
• U-Boot: U-Boot ADC driver

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 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.

For the Linux kernel U-boot and OP-TEE configuration, refer to ADC device tree configuration article.

6. How to go further

See application notes:

• How to get the best ADC accuracy in STM32.

Analog-to-digital converter. The process of converting a sampled analog signal to a digital code that represents the amplitude of the original signal sample.

Central processing unit

Direct memory access

Reset and clock control

Advanced high-performance bus

Voltage reference buffer (STM32 specific)

Low-power timer (STM32 specific)

External interrupt

Board support package

Arm^® is a registered trademark of Arm Limited (or its subsidiaries) in the US and/or elsewhere.

Cortex^®

Read only memory

Trusted firmware for Arm^® Cortex^®-A

Boot loader stage 2

Das U-Boot -- the universal boot loader (see U-Boot)

Open portable trusted execution environment

Linux^® is a registered trademark of Linus Torvalds.

USB Type-C^® Connector System Software Interface - NEW

Hardware abstraction layer

Analog-to-digital converter. The process of converting a sampled analog signal to a digital code that represents the amplitude of the original signal sample.

Central processing unit

Direct memory access

Reset and clock control

Advanced high-performance bus

Voltage reference buffer (STM32 specific)

Low-power timer (STM32 specific)

External interrupt

Board support package

Arm^® is a registered trademark of Arm Limited (or its subsidiaries) in the US and/or elsewhere.

Cortex^®

Read only memory

Trusted firmware for Arm^® Cortex^®-A

Boot loader stage 2

Das U-Boot -- the universal boot loader (see U-Boot)

Open portable trusted execution environment

Linux^® is a registered trademark of Linus Torvalds.

USB Type-C^® Connector System Software Interface - NEW

Hardware abstraction layer

USB port or connector