A flat fee, also referred to as a flat rate or a linear rate, refers to a pricing structure that charges a single fixed fee for a service, regardless of usage.[1] Less commonly, the term may refer to a rate that does not vary with usage or time of use.
Synchronous: interrupt occurs as a result of current process, otherwise asynchronous. User requested: interrupt occurs because of direct result by user task, otherwise coerced. Maskable: if desired the interrupt can be disabled by a user task, otherwise unmasked.
This interrupt handling code is often called an ISR (interrupt service routine). When the ISR is finished, it returns to the code that was running prior to the interrupt, which then resumes running with no awareness that it has been pre-empted by the interrupt code.