Interfacing an I2S device to an MSP430 device application note (PDF!) from Texas Instruments:
The MSP430 series of microprocessors are fast powerful devices ideally suited for use with the various wireless transceivers offered by Texas Instruments. In streaming audio applications, however, it is desirable that the microprocessor support an audio bus to allow for interconnection to an audio CODEC.
This application note describes how to create an I2S-like bus (left-justified mode) from an SPI bus using a 4-bit counter, a ‘D’ type flip-flop, and a dual inverter gate.