1. Article purpose[edit source]
This article introduces the SAI Linux® driver for the SAI internal peripheral.
2. Short Description[edit source]
The SAI[1] Linux driver is an ASoC CPU DAI driver implemented in the Linux ALSA framework.
The SAI driver requests two clocks which can be used as parent clocks of the SAI peripheral kernel clock. The rates of these parent clocks must be respectively a multiple of 8kHz and 11.025kHz. One of these two clocks is selected at runtime through the SAI clock muxer, depending on the audio stream sampling rate.
The SAI peripheral kernel clock is shared by the two SAI sub-blocks, which involves that these two sub-blocks have to run with compatible sampling rates, when they are active at the same time.
3. Configuration[edit source]
3.1. Kernel Configuration[edit source]
Activate the SAI[1] Linux driver in the kernel configuration using the Linux Menuconfig tool: Menuconfig or how to configure kernel.
[*] Device Drivers
[*] Sound card support
[*] Advanced Linux Sound Architecture
[*] ALSA for SoC audio support
STMicroelectronics STM32 SOC audio support
[*] STM32 SAI interface (Serial Audio Interface) support
3.2. Device tree[edit source]
Refer to the SAI device tree configuration article when configuring the SAI Linux kernel driver.
4. How to use[edit source]
The SAI Linux driver can be accessed from userland through an ALSA device. Refer to ALSA overview for information on how to list and use ALSA devices.
5. How to trace and debug[edit source]
The debugfs and procfs file system can be checked to get information on the SAI driver and the resources it uses. A non-exhaustive list of these file system entries is provided below. Refer to ALSA overview for more details on debugging tools.
- debugfs entries:
- asoc: refer to ALSA_overview#How_to_monitor
- clk: refer to Clock_overview#How_to_monitor_with_debugfs to get information on clocks.
- pinctrl: refer to Pinctrl_overview#How_to_monitor to get information on pins.
- regmap: allow to monitor SAI peripheral registers.
$ cat /sys/kernel/debug/regmap/xxx.audio-controller/registers
- procfs entries:
- asound: refer to ALSA_overview#How_to_debug
- interrupts: allow to check interrupts.
$ cat /proc/interrupts
6. Source code location[edit source]
The STM32 SAI peripheral includes two independent audio subblocks that share common resources. The driver source code reflects this architecture.
sound/soc/stm/stm32_sai.c : handles common resources such as clock, interrupt, reset and shared register.
sound/soc/stm/stm32_sai_sub.c : handles the resources dedicated to each subblock.
7. References[edit source]