1. Article purpose[edit source]
The purpose of this article is to:
- briefly introduce the MDF 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 source]
The MDF (Multi-function Digital Filter) acts as an ADC interfacing with external sigma-delta modulators. The MDF digital filters provide flexible digital processing options, allowing the conversion of sigma-delta samples into PCM samples with a final resolution of up to 24 bits. It can be used in various applications, such as recording audio with MEMS microphones, metering (for instance, energy measurement with STPMS2[1]), or motor control.
The MDF peripheral provides several features, such as:
- Serial or parallel interfaces:
- External analog frontend serial interfaces (SITF), like SPI, Manchester-coded single wire interface, and clock output, for various sigma-delta modulators.
- Alternative internal digital parallel interfaces (ADCITF), from the internal ADC.
- A flexible matrix (BSMX), allowing the connection of any incoming bitstream to any filter.
- Digital filter paths (DFLT), offering various digital processing options.
- Conversions that can be launched continuously, or using various triggers, by software, TIM, LPTIM, EXTI, or synchronously with MDF filter 0.
- Event detectors: short-circuit detector (SCD) and clock absence detector.
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 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 source]
3.1.1. On STM32MP2 series[edit source]
Click on 
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 STM32 MPU Embedded Software distribution.
- ⬚ means that the peripheral can be assigned to the given boot time 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 hardware connected in the device.
The present chapter describes STMicroelectronics recommendations or choice of implementation. Additional possibilities might be described in STM32MP25 reference manuals.
| Domain | Peripheral | Boot time allocation | Comment
| |||
|---|---|---|---|---|---|---|
| Instance | Cortex-A35 secure (ROM code) |
Cortex-A35 secure (TF-A BL2) |
Cortex-A35 non-secure (U-Boot) | |||
| Analog | MDF | MDF1 | ⬚ | |||
3.2. Runtime assignment[edit source]
3.2.1. On STM32MP25x lines 
[edit source]
Click on to expand or collapse 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 is assigned by default to the given runtime context and that the peripheral is mandatory for the STM32 MPU Embedded Software distribution.
- ⬚ 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 hardware connected in the device.
The present chapter describes STMicroelectronics recommendations or choice of implementation. Additional possibilities might be described in STM32MP25 reference manuals.
| Domain | Peripheral | Runtime allocation | Comment
| |||||
|---|---|---|---|---|---|---|---|---|
| Instance | Cortex-A35 secure (OP-TEE / TF-A BL31) |
Cortex-A35 non-secure (Linux) |
Cortex-M33 secure (TF-M) |
Cortex-M33 non-secure (STM32Cube) |
Cortex-M0+ (STM32Cube) | |||
| Analog | MDF | MDF1 | ⬚OP-TEE | ☐ | ⬚ | ☐ | ||
4. Software frameworks and drivers[edit source]
Below are listed the software frameworks and drivers managing the MDF peripheral for the embedded software components listed in the above tables.
- Linux®: IIO framework or ALSA framework
- STM32Cube: HAL MDF driver
5. How to assign and configure the peripheral[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 configuration, please refer to MDF device tree configuration and MDF Linux driver articles.
6. How to go further[edit source]
The Getting started with sigma-delta digital interface[2] application note (AN4990) from STMicroelectronics applies to the DFSDM internal peripheral on the STM32MP1 series. However, the concepts explained in this document about sigma-delta modulation are relevant for the MDF peripheral also.
7. References[edit source]
- ↑ STPMS2 "Smart sensor" device
- ↑ AN4990: Getting started with sigma-delta digital interface application note
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