SAI internal peripheral
目录
Article purpose
The purpose of this article is to:
- briefly introduce the SAI 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 SAI peripheral.
Peripheral overview
The SAI (Serial Audio Interface) offers a wide set of audio protocols, such as: I2S standards (LSB or MSB-justified), PCM/DSP, TDM and S/PDIF. The SAI contains two independent audio sub-blocks. Each sub-block has its own clock generator and I/O line controller, and can be configured either as transmitter or receiver.
Features
Refer to STM32MP15 reference manuals for the complete feature list, and to the software components, introduced below, to see which features are implemented.
Security support
All the SAI instances are non secure peripherals.
Peripheral usage and associated software
Boot time
The SAI is not used at boot time.
Runtime
Overview
SAI instances can be allocated to:
- the Cortex-A7 non-secure for use in Linux with ALSA framework
- the Cortex-M4 for use in STM32Cube with STM32Cube SAI driver
Chapter #Peripheral assignment exposes which 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) |
|||
| Audio | SAI | ALSA framework | STM32Cube SAI driver | ||
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, then manually completed (particularly for external peripherals), according to the information given in the corresponding software framework article.
Configuration in Cortex-A7 non-secure software
When the Arm® Cortex®-A7 core operates in non-secure access mode, the SAI is controlled by the Linux kernel framework. Refer to SAI Linux driver to drive the SAI through Linux kernel ALSA framework. Refer to Soundcard configuration and SAI device tree configuration to configure the SAI through the Linux kernel device tree[1].
Arm® Cortex®-M4 software configuration
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Peripheral assignment
Internal peripherals assignment table template
| rowspan="4" | Audio | rowspan="4" | SAI | SAI1 | | ☐ | ☐ | Assignment (single choice) |- | SAI2 | | ☐ | ☐ | Assignment (single choice) |- | SAI3 | | ☐ | ☐ | Assignment (single choice) |- | SAI4 | | ☐ | ☐ | Assignment (single choice) |-
|}
How to go further
STM32H7 SAI training [2] introduces the SAI features and applications. The SAI versions in STM32H7 and STM32MP15 are very close. In consequence this training is also relevant for STM32MP15. The user should refer to the STM32MP15 reference manuals for a complete description.
