With the code below, execution never gets to the TWI_ISR() function. My suspicion is that SIG_P14 is wrong but I can't find a definitive answer in the dsp docs. The run time manual skips from SIG_P13 to SIG_P15 and doesn't list P14, but the c compiler manual talks about DPI on P14.
/* Unmask the TWI master mode interrupt sources. */
*pTWIIMASK = TWIMCOM | TWIMERR | TWITXINT | TWIRXINT;
/* Route the TWI interrupt to default DPI. */
*pDPI_IRPTL |= TWI_INT;
/* Enable the TWI (default DPI) interrupt. */