How to handle if SPI slave receives less words when chip select goes high?

[MSipo]

I have setup the MCU as an SPI slave that will receive 15 words.

How can I handle if the master sends less than 15 words?

If the master sends less than 15 words I don't get any call to HAL_SPI_TxRxCpltCallback().

The NSS pin is selected as "Hardware NSS Input Signal".

I have not been able to activate an external interrupt on the NSS pin so I can't detect NSS rising edge.

[TDK]

One option is to make the CS pin an EXTI interrupt source, and when it goes high, reset the SPI interface and/or interpret the amount of data it already sent.

The pin can act as NSS and EXTI at the same time.

[MSipo]

I tried to use the pin as NSS and EXTI at the same time but it didn't work. But I did route it to a separate pin and there it works.

What do I need to do to make it work on the same pin?

 

[TDK]

In CubeMX, right click the pin -> Pin Stacking. Then select the EXTI function.

It looks like CubeMX generates the initialization in the correct order to allow this to work, but I didn't test. Try it. If it doesn't, you will need to do the EXTI configuration in user code.

[MSipo]

Thank you. I didn't know about the pin stacking in CubeMx :thumbs_up:

[MSipo]

Got it to work now. Found more info at https://community.st.com/t5/stm32-mcu-products/is-it-possible-to-use-multiple-functions-on-a-single-pin-on/m-p/134013 

CubeMX doesn't support this (both EXTI and NSS at the same time). So I had to manually add a rising edge EXTI on that pin. Now it works.