Interrupts vs. Exceptions

Interrupts: Asynchronous

Exceptions: Synchronous

Which RISC-V instructions don’t ever result in exceptions? None.

Types of Exceptions

• Arithmetic: Overflow, Underflow, Div by Zero
• Faults: Page fault, Invalid Opcode
• Errors: Parity
• Traps: Breakpoint

Precise Exceptions

• All instructions are atomic: on exception, all previous instructions are executed
• The faulting instruction may or may not have been executed, depending on the definition of the architecture and the cause of the exception

Speculative Execution + Faults

• Reorder Buffer: commit faults when need to commit

Caches

Why memory wall?

• Storage tech
• Physical distance
• Bus bandwidth (more cores, etc.)