Advanced ISA Experimentation Tool for COE-308: Empowering Computer Architecture Learning

1. Educational Computer Architecture Experimentation Tool Dr. Abdelhafid Bouhraoua

2. Needs • COE-308 course material is mainly centered around ISA and Design. • COE-308 course material focuses on: • Performance issues around the ISA. • Design of the Datapath and Control • Simple Memory Architecture • Existing tools are mainly assemblers • Need an ISA/Datapath/Memory Experimentation tool

3. Existing Capabilities • MIPS Instruction Set Assembler • SPIM, DLX and others • SPIM and DLX • Enable programming assignments only • No support for ISA modification • No Performance Measurement • No Datapath design trade-offs experimentation capabilities • Others • Very advanced research tools that are less suitable for entry-level education purpose

4. General Requirements • Ability to fully define ISAs • Hardware elements • Instruction Sets • Ability to describe instruction execution flow. • Ability to define internal datapath blocks • Ability to simulate execution of sample programs • Ability to measure performances metrics (execution time)

5. Defining ISAs • Define Hardware elements and characteristics visible at the programmer level • Registers • Operations • Execution flow • Define Instruction Set • Instructions • Instruction Description • Automatic Generation of the Assembler and Simulator for the target machine • Includes syntax check • Includes execution traces • Includes measurement of certain metrics and execution statistics

6. Fixed Choices • Single Execution Unit • No Floating Point Unit (at the beginning) • Two separate Instructions and Data Memory Access Buses • Single Execution Mode • No privileged/supervisor mode support • Single Instruction Set • No Dual instruction set support • Single Hardware Interrupt

7. Organization • Organized as Several Areas: • Objects Area • Instruction Set Area • Datapath Area • Assembler Area • Simulator Area Each Area is linked to the others through the use of its defined parameters in the definition of the other area parameters Example: A Register, defined in the Objects area can be referenced in the definition of an instruction in the Instruction Set Area

8. Defining the Objects • Execution Unit • Clock Cycles per Instruction • Single Clock Cycle per Instruction • Multiple Clock Cycles per Instruction • Pipelined/non-pipelined • Pipeline stages • Number of Operands per instruction • 1, 2 or 3 operands per instruction • Registers • Single or Array • If Array define its indexes (From k to n+k) • Size (number of bits) • Label • Operations • Select Operations used by Instruction Set from a set of predefined operations (+, -, x, shift, and, or, …) • Define new operations as combination of existing operations

9. Defining the Instruction Set • Mnemonics • Label • Number of Variants • Addressing Modes • Addressing mode selection for every variant • Possible Operands Selection for every operand from the list of already defined registers or addressing modes • Description • Cycle per Cycle • Select operation (from list of defined operations) • Use non-visible (to the programmer) temporary registers or hardware functional blocks (defined in datapath area) in description

10. Defining the Datapath • Use Existing Hardware Blocks from Library • ALU • Register File • Muxes • Customize the blocks • Size • Define new blocks using hierarchical definitions • Define block Connections • Text Definition • Possible Definition of Buses • Buses can be Tristate • Map Objects to Hardware Blocks

11. The Assembler • Choose the Syntax for representing • Instruction line • Comment • Data Definition • Static Memory Allocation • Every Addressing Mode used in the ISA • Choose Policy for Program location in Memory • Editor for writing programs • Assembler translates text programs into object code referencing Instruction Descriptions of Instruction Variants

12. The Simulator • Executes object code • Uses a flat memory model • Define Address Boundaries (for debugging) • Detects (during execution) • Structural Conflicts • Dependencies • Contradictory Definitions • Integrates measurement of important metrics • Code density • Execution Time • Program Size

13. Summary • Provides the students with a powerful experimentation tool • Designed to Show the dependenciesthat exist between: • The Instruction Set • The Operations • The Hardware Elements • The Datapath • Suitable for Pipelined and Non-pipelined Architectures • COE-308 and COE-205 (Computer Organization) as well

14. Usage • Assignments can be: • Given an Instruction set; define a possible implementation (with provided guidelines) • Given a given datapath; define a suitable instruction set • Evaluate the performances of two different implementations of the same Instruction Set

15. Aspect • Toolset composed of multiple interacting independent software module • Some are GUI-based • Some are Text/Command Line based • Define/Use Existing language to describe: • Instruction Set (Assembly side) • Datapath • Data Entry • Probes

16. Extension of Usage • Extra module for Verilog/VHDL generation • Generation of Datapath Unit Verilog model • Generation of Control Unit Verilog model • Generation of Testbench Verilog Model • Generation of Memory Verilog model (to accept programs) • Interface between assembler and Verilog Model

17. Conclusion Computer Architecture Experimentation Toolset for ISA/Processor Design and Education. Easily Realizable if developed in modules (each module developed as a Senior Project) If Possible: Collaboration with ICS department (software intensive) project. Web-based Interface ?