SPI_connect — connect a procedure to the SPI manager
int SPI_connect(void)
SPI_connect opens a connection from a
procedure 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 procedures.
SPI_OK_CONNECTon success
SPI_ERROR_CONNECTon error