Hm, that doesn't seem quite right... the DMA transfer size (SSIZE and DSIZE) shouldn't vary with the number of shifters, it should always be 32 bits so the DMA engine copies a word from memory into each FlexIO shifter buffer.
Try this code. It runs without errors and triggers the DMA callback, although I can't confirm whether the data is shifting out properly since I don't have an oscilloscope anymore. It should work with 4 shifters and I think it works with 8 shifters too.
Try this code. It runs without errors and triggers the DMA callback, although I can't confirm whether the data is shifting out properly since I don't have an oscilloscope anymore. It should work with 4 shifters and I think it works with 8 shifters too.