Interrupts are outside the scope of SPI; their usage is neither forbidden nor specified, and so may be implemented optionally.

From Master → Slave:

• Microcontrollers used as SPI slaves often have hardware support for:
  • Receive interrupts: Triggered when data is received.
  • Overflow interrupts: Triggered if receive FIFO buffer overflows.
  • SS line interrupts: Triggered when Slave Select (SS) goes low or high, allowing the slave to react immediately.

From Slave → Master:

• Some SPI slaves send interrupt signals back to the master using a separate wire.
• Examples:
  • Pen-down interrupt (touchscreen sensors)
  • Thermal alert (temperature sensors)
  • Alarm outputs (RTC chips)
  • SDIO signals
  • Audio jack insertion detection
• Alternative: If no interrupt pin is available, the master can poll the slave at regular intervals (similar to USB polling).