Difference between revisions of "ADC internal peripheral"

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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 application notes:

  • How to get the best ADC accuracy in STM32[8].
  • Getting started with STM32MP15 Series hardware development (AN5031)[9].
    It deals with analog domain power supply and reference voltage.

5 References[edit]

  1. ↑ DMA internal peripheral
  2. ↑ RCC internal peripheral
  3. ↑ VREFBUF internal peripheral
  4. ↑ Regulator overview
  5. ↑ TIM internal peripheral
  6. ↑ LPTIM internal peripheral
  7. ↑ EXTI internal peripheral
  8. ↑ How to get the best ADC accuracy in STM32, by STMicroelectronics
  9. ↑ Getting started with STM32MP15 Series hardware development, by STMicroelectronics 




==Article purpose==
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.

==Peripheral overview==
The STM32 '''ADC''' is a successive approximation analog-to-digital converter.

===Features===
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'''<ref name="DMA internal peripheral">[[DMA internal peripheral]]</ref>.
* 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<ref name="RCC internal peripheral">[[RCC internal peripheral]]</ref> sources (Synchronous or Asynchronous clock).
* The '''common reference voltage''' can be provided by either VREFBUF<ref name="VREFBUF internal peripheral">[[VREFBUF internal peripheral]]</ref> or any other external regulator<ref name="Regulator overview">[[Regulator overview]]</ref> 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<ref name="TIM internal peripheral">[[TIM internal peripheral]]</ref>, LPTIM<ref name="LPTIM internal peripheral">[[LPTIM internal peripheral]]</ref> and EXTI<ref name="EXTI_internal_peripheral">[[EXTI internal peripheral]]</ref>.

Refer to [[STM32MP15 resources#Reference manuals|STM32MP15 reference manuals]] for the complete features list, and to the software components, introduced below, to know which features are really implemented.<br>


===Security support===
The ADC is  a '''non-secure''' peripheral.

==Peripheral usage and associated software==
===Boot time===
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.

===Runtime===
====Overview====
The ADC can be allocated to:
* the Arm<sup>&reg;</sup> Cortex<sup>&reg;</sup>-A7 non-secure core to be used under Linux<sup>&reg;</sup> with [[IIO overview|IIO]] framework.
or
* the Arm<sup>&reg;</sup> Cortex<sup>&reg;</sup>-M4 to be used with STM32Cube MPU Package with [[STM32CubeMP1 architecture|ADC HAL driver]].

The [[#Peripheral assignment|Peripheral assignment]] chapter describes which peripheral instance can be assigned to which context.

====Software frameworks====
{{:Internal_peripherals_software_table_template}}
 | Analog
 | [[ADC internal peripheral|ADC]]
 | 
 | [[IIO overview|IIO framework]]
 | [[STM32CubeMP1 architecture|STM32Cube ADC driver]]
 |
 |-
 |}

====Peripheral configuration====
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.

====Peripheral assignment====
{{:Internal_peripherals_assignment_table_template}}<onlyinclude>

 | rowspan="1" | Analog
 | rowspan="1" | [[ADC internal peripheral|ADC]]
 | ADC
 | 
 | <span title="assignable peripheral" style="font-size:21px">☐</span>

 | <span title="assignable peripheral" style="font-size:21px">☐</span>

 | Assignment (single choice)
 |-</onlyinclude>

 |}

==How to go further==
See application notes:
* How to get the best ADC accuracy in STM32<ref>[http://www.st.com/content/ccc/resource/technical/document/application_note/group0/3f/4c/a4/82/bd/63/4e/92/CD00211314/files/CD00211314.pdf/jcr:content/translations/en.CD00211314.pdf How to get the best ADC accuracy in STM32], by STMicroelectronics</ref>.
* Getting started with STM32MP15 Series hardware development (AN5031)<ref>[https://www.st.com/resource/en/application_note/dm00389996.pdf Getting started with STM32MP15 Series hardware development], by STMicroelectronics</ref>.<br/> It deals with analog domain power supply and reference voltage.

==References==<references/>

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{{PublicationRequestId | 8309 | 2018-08-07 | AlainF}}

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