DFSDM internal peripheral

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 three runtime contexts and linked to the corresponding software components
• explain, when needed, how to configure the DFSDM peripheral.

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...

Features

The DFSDM peripheral provides several features, among which:

• Up to 8 external analog frontend serial interfaces (SPI, manchester coded single wire interface, clock output), for various sigma-delta modulators
• Up to 8 internal digital parallel interfaces (from internal ADC or memory data stream via DMA or CPU)
• Up to 6 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

Refer to STM32MP15 reference manuals for the complete features list, and to the software components, introduced below, to know which features are really implemented.

Security support

The DFSDM is a non-secure peripheral.

Peripheral usage and associated software

Boot time

The DFSDM is not used at boot time.

Runtime

Overview

The DFSDM can be allocated to:

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

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• the Arm^® Cortex^®-M4 for using in STM32Cube with STM32Cube DFSDM driver.

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

Software frameworks

Domain	Peripheral	Software frameworks			Comment
		Cortex-A7 secure (OP-TEE)	Cortex-A7 non-secure (Linux)	Cortex-M4 (STM32Cube)
Analog	DFSDM		Linux IIO framework Linux ALSA framework	STM32Cube DFSDM 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 DFSDM device tree configuration and DFSDM Linux driver articles.

Peripheral assignment

Internal peripherals assignment table template

| rowspan="1" | Analog
| rowspan="1" | DFSDM
| DFSDM
| 
| ☐
| ☐
| Assignment (single choice)
|-

|}

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

References

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