13.2.4.4.2 TX Under-Run

A Tx under-run condition arises when a channel requests to send data while no data is available in the transmit FIFO. For example, when the SPI controller operates in slave mode and receives a request to send data, when no data is available in transmit FIFO. The corrective action for the bus master is to write data into the transmit FIFO. The status flags (TXFIFOEMP or TXFIFOEMPNXT of the Table 13-11 register) indicate whether the FIFO is empty or will be empty after the next read operation.