13.2.2.6.7 Under-Run in Slave Mode

Under normal operating conditions, the SPI slave core in slave mode has a transmit FIFO under-run condition as the master initiates transfers when the slave transmit FIFO is empty (or attempts to transmit data faster than the slave processor loads data).The core's operation can be modified by setting FRAMEURUN (Table 13-9 register). Once set, the core ignores the under-run conditions and simply transmit zero frames when the transmit FIFO is empty at the start of a series of frames. If the first data frame of a packet is read from the FIFO and transmitted, the under-run detection is enabled such that if the transmit FIFO fails to provide any of the rest of the data packet (assuming SPI_X_SS[x] is active for the whole packet), an over-run condition is signaled.