Interrupt service routine inconsistency

[Woelki]

Hi,

My problem is, that i want to trigger an SPI reading event, on an master timer repetition event. I registered the HAL_HRTIM_RepetitionEventCallback and start the SPI, within this function. The first problem is, that there is always a delay, that seems way too big, to start the peripheral at a CPU clock 0f 170MHZ. On the other side, that delay is not consistent, making it even harder to work with. 

This is a waveform i get. In pink is the clk line of the SPI, you can see, that for whatever reason sometimes 4 transmissions take place, eventhough only one dataframe was set up. When the light blue line goes high, the SPI should be triggered by the according ISR. I´m not sure, what im doing wrong, but i even set the HRTIM interrupts to the highest priority to service earlier. 

Here is my SPI setup. As i only want to recieve data, im using master recieve. I also tried full duplex and then i can get rid of the multiple data frames sent, but i thought this would then include dummy bytes sent and make the delay until reception longer.

 

 

[TDK]

What delay is “too big”? Consider doing this using DMA rather than code in an interrupt.

Set up SPI in full duplex mode and write to TX to trigger a transaction. Using receive only mode may get additional clocks. Read from RX using DMA.