- * wait for the last transaction shifted out. yes, these two
- * while loops are supposed to be the same (see the HRM).
+ * wait for the last transaction shifted out. HRM states:
+ * at this point there may still be data in the SPI DMA FIFO waiting
+ * to be transmitted ... software needs to poll TXS in the SPI_STAT
+ * register until it goes low for 2 successive reads