MDMA internal peripheral

1. Article purpose

The purpose of this article is to:

• briefly introduce the MDMA 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 necessary, how to configure the MDMA peripheral.

2. Peripheral overview

The MDMA is used to perform high-speed data transfers between memory and memory or between peripherals and memory. The MDMA controller offers 32 channels. The selection of the device connected to each channel and controlling DMA transfers is done in MDMA peripheral.

Among all the requestor lines described in the STM32MP15 reference manuals, DMA channels are the only lines that allow to perform transfers with chained DMA and MDMA (refer to DMA internal peripheral article). As a result, when a device is not connected to the MDMA, it is anyway possible to operate in DMA mode via the DMA controller and chain DMA and MDMA.

2.1. Features

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

2.2. Security support

The MDMA is a secure peripheral. This means that it performs each transfer in the context of the master that requested it:

• a transfer requested by the Arm^® Cortex^®-A7 non-secure core propagates non-secure accesses to the targeted device and/or memory.
• a transfer requested by Arm Cortex-A7 secure core propagates secure accesses to the targeted device and/or memory.

3. Peripheral usage and associated software

3.1. Boot time

The MDMA is used at boot time by the FMC.

3.2. Runtime

3.2.1. Overview

The MDMA is visible from the Arm Cortex-M4 core. However, it is not supported in this context by STM32MPU Embedded Software distribution.

As stated in the 'Security support' chapter above, the MDMA is a secure peripheral. This means that its channels have to be allocated to:

• the Arm Cortex-A7 non-secure core to be controlled in Linux^® by the dmaengine framework

and

• the Arm Cortex-A7 secure core to be controlled by the MDMA OP-TEE driver
  

STM32CubeMX allows to distinguish between non-secure and secure channels, among all the available channels.

3.2.2. Software frameworks

Domain	Peripheral	Software frameworks			Comment
		Cortex-A7 secure (OP-TEE)	Cortex-A7 non-secure (Linux)	Cortex-M4 (STM32Cube)
Core/DMA	MDMA	OP-TEE MDMA driver	Linux dmaengine framework

3.2.3. Peripheral configuration

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

3.2.4. Peripheral assignment

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)
Core/DMA	MDMA	MDMA	☐	☐		Shareable (multiple choices supported)

4. How to go further

Not applicable

Direct Memory Access

Open Portable Trusted Execution Environment

Direct Memory Access

Open Portable Trusted Execution Environment