void ctl_spi_lock_bus(CTL_SPI_BUS_t *self);
ctl_spi_lock_bus acquires the bus lock mutex of the SPI bus self. If there is no mutex associated with the bus self, ctl_spi_lock_bus returns immediately.
All locks of the SPI bus by ctl_spi_lock_bus must be paired with a call to ctl_spi_unlock_bus to release the lock.
Because mutexes can be locked multiple times, you can use ctl_spi_lock_bus to ensure exclusive use of the bus in order to issue a sequence sequence of SPI transactions without interruption.