SPIS spi_transceive returns but no data in rx/tx buffers

[Anthony Ambuehl]

NCS v2.3.0

nrf5340dk_nrf5340_cpuapp_ns

Devicetree is configured so SPI2 is a SPIS.  

My calls to spi_transceive are waiting for the SPI operation but when the spi operation is complete spi_transceive returns but rx and tx data sent is 0.

I have a SPIS POC which is working but it is not in a TFM environment.   In the POC (non-TFM) environment I confirm the SPIS2 secure peripheral settings are identical to the settings configured into the non-secure peripheral.  The only difference is the "amount" register for secure peripheral reports 0 data received.

Any suggestions why no data would be received?  

[Anthony Ambuehl]

As another data point, I put my complete module for the SPIS driver into a non-TFM environment and it is working fine there, so this seems to be somehow related to the TFM non-secure environment.  Both environments used identical device tree configuration and hardware.  

[Anthony Ambuehl]

I found the root cause.  On nrf5340dk the pins P1.0 and P1.1 are used by the cpunet for the UART.