Irrespective of whether the TWI has to be used as master or slave, the following code should be used to configure the SRU for TWI:
// TWI Data
SRU(LOW,DPI_PBxx_I);
SRU(TWI_DATA_PBEN_O,DPI_PBENxx_I);
SRU(DPI_PBxx_O,TWI_DATA_I);
// TWI Clock
SRU(LOW,DPI_PByy_I);
SRU2(TWI_CLK_PBEN_O,DPI_PBENyy_I);
SRU(DPI_PByy_O,TWI_CLK_I);
where the value of xx and yy can be 0/1.../14.
The reason is that even the slave may drive the CLK line for clock stretching and DATA line for acknowledgement.