SPI_connect
SPI_connect, SPI_connect_ext — connect a C function to the SPI manager
Synopsis
int SPI_connect(void)
int SPI_connect_ext(int options)
Description
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: 
- SPI_OPT_NONATOMIC
- Sets the SPI connection to be nonatomic, which means that transaction control calls - SPI_commit,- SPI_rollback, and- SPI_start_transactionare allowed. Otherwise, calling these functions will result in an immediate error.
SPI_connect() is equivalent to SPI_connect_ext(0). 
Return Value
- SPI_OK_CONNECT
- on success 
- SPI_ERROR_CONNECT
- on error 

