What could cause a SPI slave callback function to not fire properly

Hello

I’m trying to send a message from a STM32F103ZG16 to a connect ME 9210 C module using SPI and then get the me9210 module to reply back.

I’m using the stm32 as a spi master and the me9210 as slave. So the stm32 polls the me9210 regularly to check if it’s ready to receive or have data to send.

The initial message originating from the stm32 gets transmitted by the DMA just fine, it’s picked up by the me9210 which then proceeds to queue up a reply.

However, after the initial message is sent, the callback function in the NASpiSlaveBufferType no longer seem to execute, despite several poll checks from the stm32. I.e. the callback function seems to work up until the point where the initial message is received by the slave.

Is there anything in particular that could cause the spi slave return funcion not to execute properly?

Do you have a scope or SPI/signal analyzer connected. Can you see what exactly is happening on the bus?