What are Exceptions and Interrupts?

An exception is any event that disrupts the normal execution of the processor and forces the processor into execution of special instructions in a privileged state. Exceptions can be classified into two categories: synchronous exceptions and asynchronous exceptions.
Exceptions raised by internal events, such as events generated by the execution of processor instructions, are called synchronous exceptions.
Examples of synchronous exceptions include the following:
1.On some processor architectures, the read and the write operations must start at an even memory address for certain data sizes. Read or write operations that begin at an odd memory address cause a memory access error event and raise an exception (called an alignment exception ).
2.An arithmetic operation that results in a division by zero raises an exception.

Exceptions raised by external events, which are events that do not relate to the execution of processor instructions, are called asynchronous exceptions. In general, these external events are associated with hardware signals. The sources of these hardware signals are typically external hardware devices.
Examples of asynchronous exceptions include the following:
1.Pushing the reset button on the embedded board triggers an asynchronous exception (called the system reset exception ).
2.The communications processor module that has become an integral part of many embedded designs is another example of an external device that can raise asynchronous exceptions when it receives data packets.

An interrupt, sometimes called an external interrupt, is an asynchronous exception triggered by an event that an external hardware device generates. Interrupts are one class of exception. What differentiates interrupts from other types of exceptions, or more precisely what differentiates synchronous exceptions from asynchronous exceptions, is the source of the event.
The event source for a synchronous exception is internally generated from the processor due to the execution of some instruction. On the other hand, the event source for an asynchronous exception is an external hardware device.
Applications of Exceptions and Interrupts :
In general, exceptions and interrupts help the embedded engineer in three areas:
1.internal errors and special conditions management,
2.hardware concurrency, and
3.service requests management.

For example, an embedded application running on a core processor issues work commands to a device. The embedded application continues execution, performing other functions while the device tries to complete the work issued. After the work is complete, the device triggers an external interrupt to the core processor, which indicates that the device is now ready to accept more commands. This method of hardware concurrency and use of external interrupts is common in embedded design.