SAI I2S Mono Mode Not An Option

[SHamm.18]

When using SAI for I2S, STM32CubeIDE does not give you the option to choose Mono mode. It's only option is Stereo Mode. However, STM32 SAI HAL supports both SAI_STEREOMODE as well as SAI_MONOMODE, so I think this should be an option.

[Khouloud ZEMMELI]

​Hello @SHamm.18​ ,

Could you please share your project ? I need to know which serie and version used.

Best Regards,

Khouloud

[SHamm.18]

I am using a Nucleo-L432KC with STM32CubeIDE 1.2.0. If I enable SAI1 in I2S mode, the only option is for Output Mode is Stereo, though the SAI HAL file supports Mono mode as well.

[waclawek.jan]

I2S as a standard bus is inherently and specifically 2 channel.

From this viewpoint, what would you expect from a mono setting to do? What is your target codec?

JW

[SHamm.18]

I am using I2S with a mono .wav file. If I use I2S in stereo mode, the .wav file is played twice as fast. By manually changing  hsai_BlockA1.Init.MonoStereoMode to mono mode in sai.c, the .wav file plays normally

[victagayun]

Hello I am using STM32F407 discovery kit, CubeIDE 1.8.0 and FW_F4 V1.26.2.

I plan to connect the mono mic via I2S as well and should be connected in mono mode.

Where do you get to change hsai_BlockA1.Init.MonoStereoMode to mono mode?

I cannot seem to find this code.

I am looking in:

MX_I2S2_Init(),

stm32f4xx_hal_i2s.h,

stm32f4xx_hal_i2s_ex.h, and

stm32f4xx_hal_i2s.c.

Where should I look for to modify?

[waclawek.jan]

Well, given CubeMX is just a clicking configurator to Cube, if there's a working setup in Cube, it probably should be settable in CubeMX.

Nevertheless, I was still curious, what does that mean from I2S point of view. but reading the I2S chapter in RM, it's probably just setting the SAI_xCR1.MONO bit, which in Tx duplicates slot 0 data into slot 1 in hardware, and in Rx discards slot 1 data (this ought to be borne in mind when using this feature for Rx).

JW

[Piranha]

That MONO bit is a really nice option if one needs to work with mono streams, because then you don't have to waste CPU and RAM on repacking that unnecessary second channel. :)

[Khouloud ZEMMELI]

​Hello @SHamm.18​ , You're right, issue confirmed and it will be fixed.

Best Regards,

Khouloud

[Alexmouse]

Where do I find this bit on STM32F411?

[waclawek.jan]

STM32F411 does not have the SAI interface.

JW