SPRUII0F May 2019 – June 2024 TMS320F28384D , TMS320F28384D-Q1 , TMS320F28384S , TMS320F28384S-Q1 , TMS320F28386D , TMS320F28386D-Q1 , TMS320F28386S , TMS320F28386S-Q1 , TMS320F28388D , TMS320F28388S
The FSI transmitter has a 16-word buffer that the FSI transmitter pulls data to transmit. This buffer is implemented as a circular buffer, not a FIFO, so some care must be taken to properly interpret buffer overrun and underrun, as well as the TX_BUF_PTR_STS register. These flags and pointers work under the assumption that the software or DMA is using the buffer as a circular buffer. This mode of operation is the only way that the overrun, underrun, and pointer status are meaningful. If data is being sourced by the DMA and there is some other periodic trigger mechanism trying to initiate transfers, underrun becomes a critical error. If an underrun happens, a buffer went out of sync. This not only affects the current transfer, but can also affect all future transfers due to the ring buffer. Under such conditions, the underrun needs a soft reset to cleanly recover. Alternately, the software can manually stop the transmitting, reset the buffer pointers, clear the remaining error conditions, and then restart transmission. The software method involves a few steps, while the soft reset is a single action and makes sure of a full reset of the control registers.
Due to the flexibility of the transmit buffer, software can implement a simple ping-pong buffer or randomly load and send from any location of the buffer. If the buffer is used in this manner, error flags and status fields can be ignored without adversely affecting the transmitter capability. Additionally, the CURR_WORD_CNT is also invalid if used in this way. The application can set the buffer pointer manually by writing the 4-bit index to TX_BUF_PTR_LOAD. This forces the transmitter to start picking the data from the indicated location in the buffer.