ADC internal peripheral

1 Article purpose[edit]

The purpose of this article is to

  • briefly introduce the ADC peripheral and its main features
  • indicate the level of security supported by this hardware block
  • explain how each instance can be allocated to the three runtime contexts and linked to the corresponding software components
  • explain how to configure the ADC peripheral.

2 Peripheral overview[edit]

The STM32 ADC is a successive approximation analog-to-digital converter.

2.1 Features[edit]

The STM32MP15 has one ADC block with two physical ADCs:

  • Configurable resolution: 8, 10, 12, 14, 16 bits.
  • Each ADC has up to 20 multiplexed channels (including 6 internal channels connected only to ADC2).
  • The conversions can be performed in single, continuous, scan or discontinuous mode.
  • The result can be read in a left- 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.
  • A common input clock for the two ADCs, which can be selected between 2 different clock[2] sources (Synchronous or Asynchronous clock).
  • 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 background
  • Injected conversions have higher priority, and so have the ability to interrupt the regular sequence (either triggered in SW or HW). 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 STM32MP15 reference manuals for the complete features list, and to the software components, introduced below, to know which features are really implemented.

2.2 Security support[edit]

The ADC is a non-secure peripheral.

3 Peripheral usage and associated software[edit]

3.1 Boot time[edit]

The ADC is usually not used at boot time. But it may be used by the SSBL (see Boot chains overview), to check for power supplies for example.

3.2 Runtime[edit]

3.2.1 Overview[edit]

The ADC can be allocated to:

  • the Arm® Cortex®-A7 non-secure core to be used under Linux® with IIO framework.

or

  • the Arm® Cortex®-M4 to be used with STM32Cube MPU Package with ADC HAL driver.

The Peripheral assignment chapter describes which peripheral instance can be assigned to which context.

3.2.2 Software frameworks[edit]

Domain Peripheral Software frameworks Comment
Cortex-A7
secure
(OP-TEE)
Cortex-A7
non-secure
(Linux)
Cortex-M4

(STM32Cube)
Analog ADC IIO framework STM32Cube ADC driver

3.2.3 Peripheral configuration[edit]

The configuration is applied by the firmware running in the context to which the peripheral is assigned. The configuration by itself can be performed via the STM32CubeMX tool for all internal peripherals. It can then be manually completed (especially for external peripherals) according to the information given in the corresponding software framework article.

For the Linux kernel configuration, please refer to ADC device tree configuration and ADC Linux driver articles.

3.2.4 Peripheral assignment[edit]

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.
  • 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 a runtime 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)
Analog ADC ADC Assignment (single choice)

4 How to go further[edit]

See the application note:

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

5 References[edit]





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

voltage reference buffer (STM32 specific)

low-power timer (STM32 specific)

External Interrupt

Second Stage Boot Loader

Microprocessor Unit

Open Portable Trusted Execution Environment

Attachments

Discussions