SPI_connect, SPI_connect_ext — connect a C function to the SPI manager
SPI_connect opens a connection from a C function invocation to the SPI manager. You must call this function if you want to execute commands through SPI. Some utility SPI functions can be called from unconnected C functions.
SPI_connect_ext does the same but has an argument that allows passing option flags. Currently, the following option values are available:
Sets the SPI connection to be nonatomic, which means that transaction control calls
SPI_start_transactionare allowed. Otherwise, calling these functions will result in an immediate error.
SPI_connect() is equivalent to