Last edited one month ago

STM32MP2 ADC internal peripheral

Applicable for   STM32MP23x lines  STM32MP25x lines

1. Article purpose[edit | edit source]

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[edit | edit source]

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 More info.png ADC1 18 2
ADC2 14 5
STM32MP23x lines More info.png ADC1 18 2
ADC2 14 6
ADC3 14 6
STM32MP25x lines More info.png ADC1 18 2
ADC2 14 6
ADC3 14 6
Info white.png Information
ADC1 and ADC2 are tightly coupled on STM32MP23x lines More info.png and STM32MP25x lines More info.png 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[1].
  • 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[2] independently from the AHB bus clock that is used to access the ADC registers.
  • The common reference voltage can be provided by either VREFBUF[3] or any other external regulator[4] 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[5], LPTIM[6], and EXTI[7].

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 STM32MP21x lines More info.png[edit | edit source]

Click on How to.png 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 How to.png
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 More info.png[edit | edit source]

Click on How to.png 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 How to.png
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 More info.png[edit | edit source]

Click on How to.png 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 How to.png
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[edit | edit source]

3.2.1. On STM32MP21x lines More info.png[edit | edit source]

Click on How to.png 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 How to.png
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 More info.png[edit | edit source]

Click on How to.png 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 How to.png
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 More info.png[edit | edit source]

Click on How to.png 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 How to.png
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[edit | edit source]

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

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.

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

6. How to go further[edit | edit source]

See application notes:

  • How to get the best ADC accuracy in STM32[8].

7. References[edit | edit source]