1 / 33

Microprogramming

Microprogramming. Andreas Klappenecker CPSC321 Computer Architecture. Implementation of the Finite State Machine Control Logic. Graphical Specification of FSM. How many state bits are needed? . Two-Level Logic. Any logic function can be written in a two-level

ivo
Download Presentation

Microprogramming

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Microprogramming Andreas Klappenecker CPSC321 Computer Architecture

  2. Implementation of the Finite State Machine Control Logic

  3. Graphical Specification of FSM How many state bits are needed?

  4. Two-Level Logic Any logic function can be written in a two-level representation, e.g. the sums-of-products form E = AB ~C + AC ~B + BC ~A It uses the logical OR of products (AND ops) Contains variable or complemented variable

  5. PLA Implementation Two level logic

  6. Finite State Machine for Control Implementation:

  7. Microprogramming

  8. Motivation • The full MIPS instruction set contains over 100 instructions • Instructions can take from 1 clock cycle to more than 20 clock cycles • Pipelining will lead to explosion of states • It follows that the control will be quite complex => FSM can be cumbersome Use microprogramming!

  9. Microprogramming • Implementation of MIPS instructions as a sequence of simpler instructions • Design of the microinstruction format • Write a program • Eases implementations of pipelined processor

  10. Micro-Instructions • What is needed? • ALU control signals • Program counter control signals • Complete data path • What do we do? • Analyze what is happening at each step • Express in a column oriented way • Translate it into binary • Store it in an appropriate form

  11. A Simple Implementation

  12. Microprogram • Physical implementation: ROM or PLA • Each micro-instruction has an address • Sequentially ordered • Each sequence step is one cycle • Selection of next instruction • Address increment (sequencing field = seq) • Fetch: begins fetching the next micro-instruction (sequencing field = fetch) • Dispatch: jump to the next micro-instruction, the number i indicates the location in the dispatch table

  13. Microinstruction format

  14. Microcode: Trade-offs • Specification Advantages: • Easy to design and write • Design architecture and microcode in parallel • Implementation (off-chip ROM) Advantages • Easy to change since values are in memory • Can emulate other architectures • Can make use of internal registers • Implementation Disadvantages: SLOWER • Control is implemented on same chip as processor • ROM is no longer faster than RAM • No need to go back and make changes

More Related