Why am I unable to monitor SAI2 signals from the GPIO expansion (CN2)? STM32MP157F-DK2. All signals appear low

[ASnow.1]

I can monitor the SAI2 signals directly from the audio codec pins. The MCLK, SCLK, and Fs signals appear correctly based on my configuration but when I connect my oscilloscope to the GPIO header pins (CN2), the lines all appear low even though they are changing for the codec. This doesn't happen with the I2C1 pins connected to the audio codec. I can monitor those just fine from their respective GPIO header pins, which leads me to believe it isn't an issue with the pins being configured as alternate function.

Is there a reason or solution for this?

[Kevin HUBER · Accepted solution]

Hello @ASnow.1​  ,

I don't know if you still have the problem.

For having the signals related to SAI2 on the GPIO expansion (CN2), you have to:

• Configure the GPIO

From what I understood, you are doing a baremetal project, so you have to configure the GPIOs PF11, PI6, PI7 and PI8 directly in the code.

But I can see in your previous post: https://community.st.com/s/question/0D53W00001MYONQSA5/stm32mp157fdk2-sai-receive-fifo-not-filling-block-a-configured-as-mastertx-block-b-configured-as-slaverx

That you already did that.

• Connect the lines

Second point and I think this is your problem.

These lines are not connected by default on the DK2.

If you take a look at the Schematics of the 157F-DK2 (MB1272 v1.0):

https://www.st.com/content/ccc/resource/technical/layouts_and_diagrams/schematic_pack/group0/36/8e/ea/7a/ca/ca/4b/e4/mb1272-dk2-c01_schematic/files/MB1272-DK2-C01_Schematic.pdf/jcr:content/translations/en.MB1272-DK2-C01_Schematic.pdf

you can see in page 3 in the Audio part, that there are 4 jumper SB3, SB1, 2, 4 to have the actual connection.

 

And if you look further in the page 3, GPIO & ARDUINO part you can see:

These lines with "DNF" means that they are not connected by default on the board.

On the DK2 board, the SB1/2/3 are used by default by the internal Codec as explained in the Discovery board user manual (UM2534 rev1.0) page 13:

https://www.st.com/resource/en/user_manual/dm00591354-discovery-kits-with-stm32mp157-mpus-stmicroelectronics.pdf

For being able to get your SAI2 signals on the GPIO expansion (CN2), you have to put 0 ohm resistors on SB1, SB2, SB3 and SB4. They are visible at the back of the board near the Arduino connector CN16 and you can see that they are not connected.

Hope it helps,

Regards,

Kevin

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