- Last edited 2 years ago ago
I2S Linux driver
1 Article purpose
This article introduces the I2S Linux® driver for the SPI/I2S internal peripheral.
2 Short Description
The I2S Linux driver is an ASoC CPU DAI driver implemented in the Linux ALSA framework.
The I2S driver requests two clocks which can be used as parent clocks of the IS2 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 run-time through the I2S clock mux, depending on audio stream sampling rate.
SPI/I2S2 and SPI/I2S3 internal peripherals share the same clock mux. This may result in a conflict on clock mux configuration, if I2S2 and I2S3 are used to run audio streams having incompatible rates (i.e. rates not multiple of each other). The I2S driver does not protect by itself against such conflict.
3.1 Kernel Configuration
Activate the I2S 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 I2S interface (SPI/I2S block) support
3.2 Device tree
Refer to the I2S_device_tree_configuration article when configuring the I2S Linux kernel driver.
4 How to use
The I2S 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
The debugfs and procfs file system can be checked to get information on the I2S 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:
$ 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
sound/soc/stm/stm32_i2s.c : implements the I2S Linux driver.