CTL_STATUS_t ctl_spi_write(CTL_SPI_DEVICE_t *self, const void *tx, size_t items);
ctl_spi_write writes data to the SPI device self which must have been previously selected onto the bus by ctl_spi_select_device.
If the selected transfer width for the device self is eight bits or narrower then items bytes are written from tx. If the transfer width is wider than eight bits then item shorts are written from tx.
If tx is zero, the set idle-pattern is written to the SPI device (if the the underlying driver supports such a null transfer). Note that some SPI drivers which use DMA may not support null transfers.