@mrjoneskod you can find the interrupt service routine for SPI transfer to drivers completed at https://github.com/Duet3D/RepRapFirmware/blob/139f16f52cd30a12431bdf5884aee6bc637b26c4/src/Movement/StepperDrivers/TMC2660.cpp#L874. The ISR checks whether a transfer has been completed and if so, reads the status and kicks off another transfer.
On boards other than Duet 2 we use a separate FreeRTOS task to poll the drivers, so as to simplify the control flow and do less work in the ISR.