SPI_start_transaction - start a new transaction
void SPI_start_transaction(void)
SPI_start_transaction starts a new transaction. It can only be called
after SPI_commit or SPI_rollback, as there is no transaction
active at that point. Normally, when an SPI-using procedure is called, there
is already a transaction active, so attempting to start another one before
closing out the current one will result in an error.
This function can only be executed if the SPI connection has been
set as nonatomic in the call to SPI_connect_ext.