DFSDM internal peripheral

Applicable for

STM32MP13x lines, STM32MP15x lines

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1 Article purpose

The purpose of this article is to

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

2 Peripheral overview

The DFSDM peripheral (Digital Filter for Sigma-Delta Modulator) is used as a generic ADC. It benefits from external analog frontend interfaces and internal digital filters.
It can be used in various applications such as: audio record with MEMS microphones, energy measurement with STPMS2 for electricity meters or motor control...

2.1 Features

The DFSDM peripheral provides several features, among which:

• Serial or parallel input channels:
  • External analog frontend serial interfaces (SPI, manchester coded single wire interface, clock output), for various sigma-delta modulators
  • Alternative Internal digital parallel interfaces (from internal ADC or memory data stream via DMA or CPU)
• Digital filters, that offers up to 24-bit final ADC resolution
• Conversions that can be launched continuously, or using various triggers: by software, TIM, LPTIM, EXTI or synchronously with DFSDM filter 0
• Event detectors: analog watchdog high/low thresholds, short-circuit detector, extremes detector
• Break generation to TIM on analog watchdog or short-circuit detector events

DFSDM features	Number of channels	Number of filters
STM32MP13x lines	4	2
STM32MP15x lines	8	6

Refer to STM32MP13 reference manuals or 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

The DFSDM is a non-secure peripheral.

3 Peripheral usage and associated software

3.1 Boot time

The DFSDM is not used at boot time.

3.2 Runtime

3.2.1 Overview

The DFSDM can be allocated to:

• the Arm^® Cortex^®-A7 non-secure core to be used under Linux^® by the IIO or ALSA framework

or

• the Arm^® Cortex^®-M4 for using in STM32Cube by STM32Cube DFSDM driver (on STM32MP15x lines ).

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

3.2.2 Software frameworks

3.2.2.1 On STM32MP13x lines 

Domain	Peripheral	Software components		Comment
		OP-TEE	Linux
Analog	DFSDM		Linux IIO framework Linux ALSA framework

3.2.2.2 On STM32MP15x lines 

Domain	Peripheral	Software components			Comment
		OP-TEE	Linux	STM32Cube
Analog	DFSDM		Linux IIO framework Linux ALSA framework	STM32Cube DFSDM driver

3.2.3 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 DFSDM device tree configuration and DFSDM Linux driver articles.

3.2.4 Peripheral assignment

3.2.4.1 On STM32MP13x lines 

Click on the right to expand the legend...

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.
• ⬚ means that the peripheral can be assigned to the given runtime context, but this configuration is not supported in STM32 MPU Embedded Software distribution.
• ✓ 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 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 STM32MP13 reference manuals.

Domain	Peripheral	Runtime allocation			Comment
		Instance	Cortex-A7 secure (OP-TEE)	Cortex-A7 non-secure (Linux)
Analog	DFSDM	DFSDM		☐	Assignment (single choice)

3.2.4.2 On STM32MP15x lines 

Click on the right to expand the legend...

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.
• ⬚ means that the peripheral can be assigned to the given runtime context, but this configuration is not supported in STM32 MPU Embedded Software distribution.
• ✓ 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 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)
Analog	DFSDM	DFSDM		☐	☐	Assignment (single choice)

4 How to go further

See:

• STM32L4 System Digital Filter for SD Modulators interface, online DFSDM training with application examples from STMicroelectronics

• Getting started with sigma-delta digital interface, application note from STMicroelectronics