Q. What do you mean by Software Poll?
In this scheme on occurrence of an interrupt, processor jumps to an interrupt service program or routine whose job is to poll (roll call) every I/O interface to determine which I/O interface has caused interrupt. This may be achieved by reading status register of the I/O interface. Once correct interface is recognized processor branches to a device-service routine specific to device. The shortcoming of software poll is that it's time consuming.