Lesson 3--Intro to ISA Flashcards
3 types of instructions
- Data or memory access (load, store, etc.)
- Control flow (branch)
- Arithmetic or logic (add, subtract, etc.)
ISA design
Operation: fundamental RISC-like minimal unit of work
Instruction: Fundamental unit of encoding. Refers to a parallel set of operations
Bundle: memory aligned encoding unit
True or False: VLIW exposes a scheduler in the compiler
True. Superscalar hides this.
Memory
Off chip, not specialized, slow
Registers
On chip, connected to the logic of the processor, fast
Dependencies
RAW: True dependence
WAR: False dependence
WAW: False dependence
VLIW Design Principles
- -VLIW instructions consist of parallel operations. Compiler must guarantee safe parallel operations.
- -Simplification of HW to improve energy efficiency.
- -Latency and functional unit are exposed.
True or False: VLIW’s advantages come largely from having an intelligent compiler that can schedule many instructions simultaneously.
True
True or False: VLIW-compatible code is easily portable to hardware otehr than the chip it is designed for
False
True or False: VLIW has some problems with the inflexibility of its compiler-first design
True
Role of VLIW compilers
- Gather independent operations and bundle them into sections.
- Resolve all structural and resource hazards.
- If the VLIW is clustered, the compiler assigns operations to the clusters and generates cross cluster register references.
Horizontal Decisions
Decisions within an instruction word
Vertical Decisions
Decisions across pipelined instructions
Fixed overhead encoding
Prepend mask bits to a VLIW instruction to identify “what goes where”
Distributed encoding advantages
- -Explicitly insert stop bit for delimiter
- -Distributed and incremental encoding cost.
- -No need to compute next PC.
