I/O Control
I/O issues:
- how to start an I/O (special instructions or memory-mapped I/O
- I/O completion (interrupts)
Interrupts are the basis for asynchronous I/O
- device controller performs an operation asynch to CPU
- device sends an interrupt signal on bus when done
- in memory is a vector table containing a list of addresses of kernel routines to handle various events
- CPU switches to address indicated by vector specified by the interrupt signal