05.Exceptions Handling

Exceptions Handling

Interrupts

Interrupts are signals that alter the normal control flow of a program at runtime. An interrupt must be handled by a dedicated interrupt handler, and the architecture should be able to resume the normal execution of the program. Causes:

• Asynchronous external events:
  • I/O device reply
  • timer expiration
  • HW failure
• Synchronous internal event:
  • opcode error
  • arithmetic overflow
  • bad memory access
  • traps: traps are a mechanism used by computers to transfer control to the OS or to kernel routines in response to various events like system calls.

Interrupts can be characterized in various ways:

• Async interrupts are caused by external sources and can be handled at the end of the execution of the current instruction, making them easier to manage than sync ones.
• User request interrupts are predictable: they are treated as exceptions because they use the same mechanism. Coerced interrupts (forced) are caused by some HW event not under control of the program.
• User maskable vs user nonmaskable
• Within instructions interrupts are usually synchronous since the instruction triggers the exception. The instruction must be stopped and restarted.
• Resume vs terminate interrupts

Super exception table

Exception type	Synchronous vs. asynchronous	User request vs. coerced	Oser maskable vs. nonmaskable	Within vs. between instructions	Resume vs. terminate
I/O device request	Asynchronous	Coerced	Nonmaskable	Between	Resume
Invoke operating system Tracing instruction execution	Synchronous	User request	Nonmaskable	Between	Resume
Breakpoint Integer arithmetic overflow	Synchronous	User request	User maskable	Between	Resume
Floating-point arithmetic overflow or underflow	Synchronous	Coerced	User maskable	Within	Resume
Page fault	Synchronous	Coerced	Nonmaskable	Within	Resume
Mischaligned memory accesses	Synchronous	Coerced	User maskable	Within	Resume
Memory protection violations	Synchronous	Coerced	Nonmaskable	Within	Resume
Using undefined instructions	Synchronous	Coerced	Nonmaskable	Within	Terminate
Hardware malfunctions	Asynchronous	Coerced	Nonmaskable	Within	Terminate
Power failure	Asynchronous	Coerced	Nonmaskable	Within	Terminate