11-2-3 Loosely Coupled Configurations
A loosely coupled configuration provides the following advantages:
- High system throughput can be achieved by having more than one CPU.
- The system can be expanded in a modular form.Each bus master module
is an independent unit and normally resides on a separate PC board.
Therefore, a bus master module can be added or removed without affecting
the other modules in the system.
- A failure in one module normally does not cause a breakdown of the
entire system and the faulty module can be easily detected and replaced.
- Each bus master may have a local bus to access dedicated memory or
I/O devices so that a greater degree of parallel processing can be achieved.
In a loosely coupled multiprocessor system, more than one bus master module
may have access to the shared system bus.Since each master is running
independently, extra bus control logic must be provided to resolve the bus
arbitration problem.This extra logic is called bus access logic and
it is its responsibility to make sure that only one bus master at a time has
control of the bus.Simultaneous bus requests are resolved on a priority basis.
There are three schemes for establishing priority:
- Daisy chaining.
- Polling.
- Independent requesting.