Interrupt Driven Data Transfer

add

sub

and

nop

read

store

...

rti

memory

user

program

(1) I/O

interrupt

(2) save PC

(3) interrupt

service addr

interrupt

service

routine

(4)

User program progress only halted during

actual transfer

Interrupt Overhead can dominate transfer time.

1000 xfers of 1000 bytes each:

2usecs for interrupt

98usecs for service

Device xfer rate: 10 MB/s => .1usec/byte => .1ms for 1000 bytes