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How does a "slave" device get the attention of the "master"?
Interrupts.
Polling (polling interrupt)
Master (CPU/other) queries each device for its status or need for attention.
Simple design.
Heavy load on Master.
Limits number of "slaves"
Limits detection time.
Wastes CPU cycles.
USB 1,2 (low, full, high speed) uses polling - all devices are passive.
Commodore VIC 20, C64, B128
Polled a list of interfaces every 50/60 times a second based on
AC electrical source.
Interrupt requests
Interrupts generated by client device to request attention of master.
Interrupts are generally prioritized.
A request from hard drive is more time sensitive than one from keyboard.
Priority of interrupts are often handled by a dedicated circuit which
delivers a general interrupt request to the master.
Master communicates with interrupt handler to determine interrupt source.
Or poles devices.
Only responds to active interrupt.