The SSI can generate interrupts when the following conditions are observed:
All of the interrupt events are ORed together before being sent to the interrupt controller, so the SSI generates a single interrupt request to the controller regardless of the number of active interrupts. Each of the four individual maskable interrupts can be masked by clearing the appropriate bit in the SSI Interrupt Mask (SSIIM) register. Setting the appropriate mask bit enables the interrupt.
The individual outputs, along with a combined interrupt output, allow the use of either a global interrupt service routine or modular device drivers to handle interrupts. The transmit and receive dynamic data-flow interrupts have been separated from the status interrupts so that data can be read or written in response to the FIFO trigger levels. The status of the individual interrupt sources can be read from the SSI Raw Interrupt Status (SSIRIS) and SSI Masked Interrupt Status (SSIMIS) registers.
The receive FIFO has a time-out period that is 32 periods at the rate of SSIClk (whether or not SSIClk is currently active) and is started when the RX FIFO goes from EMPTY to not-EMPTY. If the RX FIFO is emptied before 32 clocks have passed, the time-out period is reset. As a result, the ISR should clear the Receive FIFO Time-out Interrupt just after reading out the RX FIFO by writing a "1" to the RTIC bit in the SSI Interrupt Clear (SSIICR) register. The interrupt should not be cleared so late that the ISR returns before the interrupt is actually cleared, or the ISR may be reactivated unnecessarily.
The End-of-Transmission (EOT) interrupt indicates that the data has been transmitted completely. This interrupt can be used to indicate when it is safe to turn off the SSI module clock or enter sleep mode. In addition, because transmitted data and received data complete at exactly the same time, the interrupt can also indicate that read data is ready immediately, without waiting for the receive FIFO time-out period to complete.