Logic Synthesizer

• US 4,703,435 A
• Filed: 07/16/1984
• Issued: 10/27/1987
• Est. Priority Date: 07/16/1984
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Darringer, John A., Joyner, William H. Jr.
• Primary Examiner(s): Krass, Errol A.
• Assistant Examiner(s): Dixon, Joseph L.
• Application Number:
  US06/631,364
• Time in Patent Office: 1,198 Days
• Field of Search: 364/488, 364/489, 364/490, 364/491, 364/300, 307/303
• US Class Current: 716/103
• CPC Class Codes: G06F 30/327 Logic synthesis; Behaviour synthesis, e.g. mapping logic, HDL to netlist, high-level language to RTL or netlist

Abstract

Logic is synthesized from a flowchart-level description by first generating an AND/OR logic design, simplifying the AND/OR logic, converting the AND/OR logic to NAND or NOR logic, applying particular sequences of simplifying transformations to the NAND or NOR logic, converting the simplified NAND or NOR logic to a target technology, and simplifying the target technology where possible. The end result is an interconnection of primitives of the target technology in a language from which automated logic diagrams can be produced.

Claims

1. An automated logic synthesis method of designing, on a computer, a logic circuitry implementation in a desired technology from input data to said computer comprising a description of operating characteristics to be provided by said logic circuitry, said method comprising the steps of:

generating, via said computer, a first logic circuit design in a first logic system in accordance with said description;

simplifying said first logic design via said computer;

converting, via said computer, said simplified first logic design to a second logic design in a second logic system requiring fewer different logic operators than said first logic system, said second logic system comprising a plurality of interconnected cells and performing equivalent functions;

simplifying, via said computer, said second logic design, said step of simplifying said second logic design comprising the steps of;

applying a depth reduction sequence of logic transformations for reducing the depth of said second logic design; and

subsequently applying a size reduction sequence of logic transformations for reducing the size while possibly increasing the depth of said second logic design; and

converting, via said computer, said simplified second logic design to said desired technology.

2. A method as defined in claim 1, wherein said step of applying said depth reduction sequence of logic transformations comprises:

applying a first logic transformation set for reducing logic depth;

applying a second logic transformation set for reducing redundancy; and

applying a third logic transformation set for eliminating common terms.

3. A method as defined in claim 2, wherein said step of applying said size reduction sequence of logic transformations comprises:

applying a fourth logic transformation set for reducing logic size while possibly increasing logic depth;

applying a fifth logic transformation set for reducing redundancy; and

applying a sixth logic transformation set for eliminating common terms.

4. A method as defined in claim 3, wherein said second and fifth logic transformation sets include at least one common logic transformation. said common logic transformation being applied in said depth reduction sequence regardless of whether said common logic transformation will increase the number of cells in said second logic design and being applied in said size reduction sequence only if it will not result in an increase in said number of cells.

5. A method as defined in claim 2, wherein said step of applying said depth reduction sequence of logic transformations further comprises applying a fourth logic transformation set (e.g.. NTR8), following said third logic transformation set, for further reducing said logic depth while increasing the number of cells in said second logic design.

6. A method as defined in claim 3, wherein said converting step comprises converting said simplified second logic design to a hardware logic design in said desired technology represented as a plurality of hardware primitives. said method further comprising the step of simplifying said hardware design, said hardware simplifying step comprising:

applying a first hardware transformation set for substituting technology-specific books for predetermined patterns of said hardware primitive;

dotting signal lines to decrease the number of components in said hardware logic design, and to decrease fan-in in some portions of said hardware logic design even if the number of components in said portions is not decreased;

applying said first hardware transformation set;

correcting fan-out in said hardware logic design to a desired value;

adjusting path lengths in said hardware logic design; and

correcting fan-out to said desired value.

7. A method as defined in claim 1, wherein said step of applying said size reduction sequence of logic transformations comprises applying a first logic transformation (e.g., FACTORN) for reducing a fan-in characteristic of some portions of said second logic design in accordance with a first fan-in value.

8. A method as defined in claim 1, further comprising the step of applying a cell reduction sequence of logic transformations for reducing the number of cells in said second logic design, said cell reduction sequence being applied between said depth reduction and size reduction sequences.

9. A method as defined in claim 8, wherein said cell reduction sequence of logic transformations includes a first set of logic transformations followed by a second set of logic transformations, said second set of logic transformations comprising said depth reduction sequence of logic transformations.

10. A method as defined in claim 8, wherein said desired technology has a maximum allowable fan-in value, said step of applying said size reduction sequence of logic transformations comprising applying a first logic transformation (e.g., FACTORN) for reducing a fan-in characteristic of some portions of said second logic design in accordance with a desired fan-in value less than said maximum allowable fan-in value.

11. A method as defined in claim 10, further comprising the step of correcting the fan-in characteristics of said second logic design in accordance with said maximum allowable fan-in value subsequent to application of said size reduction sequence of logic transformations.

12. A method as defined in claim 1, wherein said depth reduction sequence of logic transformations is applied a plurality of times prior to applying said size reduction sequence of logic transformations.

13. A method as defined in claim 1, wherein said first logic design is implemented in AND/OR logic and said second logic design is implemented in NAND logic.

14. A method as defined in claim 1, wherein said first logic design is implemented in AND/OR logic and said second logic design is implemented in NOR logic.

15. An automated logic synthesis method of designing, on a computer, a logic circuitry implementation in a desired technology from input data to said computer comprising a description of operating characteristics to be provided by said logic circuitry, said method comprising the steps of:

generating, via said computer, a first logic circuit design in a first logic system in accordance with said description;

simplifying said first logic design via said computer;

converting, via said computer, said first logic design to a second logic design in a second logic system requiring fewer different logic operators than in said first logic design, said second logic design comprising a plurality of interconnected cells and performing equivalent functions as said first logic design;

simplifying said second logic design via said computer;

converting, via said computer, said simplified second logic design to a hardware design in said desired technology comprising a plurality of interconnected hardware components; and

simplifying said hardware design via said computer, said step of simplifying said hardware design comprising;

applying a first hardware transformation set for substituting technology specific components for predetermined patterns of said hardware;

dotting signal lines via said computer, to decrease the number of components in said hardware logic design and to decrease fan-in in some portions of said hardware logic design even if the number of components is said portions is not decreased;

adjusting path lengths in said hardware logic design via said computer; and

correcting fan-out in said hardware logic design to a desired value via said computer.

16. A method as defined in claim 15, wherein said step of simplifying said hardware design further comprises applying said first hardware transformation set again after said dotting step but before said adjusting step.

17. A method as defined in claim 16, wherein said step of simplifying said hardware logic design further comprises the step of correcting said fan-out in said hardware logic design after said second application of said first hardware transformation set and before said adjusting step

18. A method as defined in claim 15, wherein said hardware logic design includes inverters receiving and inverting outputs from associated components, and wherein, when said desired technology is a dual-rail technology, said step of simplifying said hardware design further comprises the step of applying a dual-rail transformation for removing some of said inverters by substituting for said inverter and opposite-phase output signal available from its associated component, said dual-rail conversion transformation being applied both prior to said step of applying said first hardware transformation and subsequent to said step of correcting fan-out.

19. A method as defined in claim 18, wherein said dual-rail conversion transformation is applied prior to said step of applying said first hardware transformation without regard to the effect of said dual-rail conversion transformation on fan-out characteristics of said hardware logic design, said dual-rail conversion transformation being applied after said step of correcting fan-out only to the extent that application of said dualrail conversion transformation will not result in fan-out exceeding said desired value.

20. A method as defined in claim 15, wherein said hardware logic design includes inverters receiving and inverting outputs from associated components, and wherein, when said desired technology is a dual-rail technology, said step of simplifying said hardware design further comprises the step of applying a dual-rail comversion transformation, prior to said step of applying said first hardware transformation, for removing some of said inverters by substituting for said some inverters an oppositephase output available from their associated components.

21. A method as defined in claim 20, wherein said step of simplifying said hardware design further comprises the step of applying said dual-rail conversion transformation subsequent to said step of correcting fan-out.

22. A method as defined in claim 21, wherein said dual-rail conversion transformation is applied prior to said application of said first hardware transformation without regard to the effect of said dual-rail conversion transformation on fan-out characteristics of said hardware logic design, and is applied subsequent to said step of correcting fan-out only to the extent that application of said dual-rail conversion transformation will not result in fan-out exceeding said desired value.

23. An automated logic synthesis method of designing, on a computer, a logic circuitry implementation in a desired technology from input data to said computer comprising a description of operating characteristics to be provided by said logic circuitry, said method comprising the steps of:

generating a first logic circuit design via said computer, in accordance with said description;

simplifying said first logic design via said computer;

converting, via said computer, said first logic design to a second logic design in a second logic system requiring fewer different logic operators than in said first logic design;

simplifying said second logic design via said computer;

converting, via said computer, said simplified second logic design to a hardware design in said desired technology comprising a plurality of interconnected hardware components and including inverters for receiving and inverting output signals from associated ones of said components; and

simplifying said hardware design via said computer, said step of simplifying said hardware logic design comprising;

applying a dual-rail conversion transformation for removing some of said inverters by substituting for said some inverters an opposite phase output signal available from their associated components, said dual-rail conversion transformation being applied without regard to the effect on fan-out characteristics of said hardware logic design;

applying a first hardware transformation set for substituting technology-specific components;

dotting signal lines in said hardware logic design;

adjusting path lengths in said hardware logic design;

correcting fan-out in said hardware logic design to a desired value; and

applying said dual-rail conversion transformation only to the extent that it does not result in a fan-out exceeding said desired value.

24. An automated logic synthesis method of designing, on a computer, a logic circuitry implementation in a desired technology from input data to said computer comprising a description of operating characteristics to be provided by said logic circuitry, said method comprising the steps of:

generating, via said computer, a first logic circuit design accordance with said description;

simplifying said first logic design via said computer;

converting, via said computer, said first logic design to a second logic design in a second logic system requiring fewer different logic operators than in said first logic design;

simplifying said second logic design via said computer;

converting, via said computer, said simplified second logic design to a hardware design in said desired technology comprising a plurality of interconnected hardware components; and

simplifying said hardware design via said computer, said step of simplifying said hardware logic design comprising selectively applying first first or second hardware transformation sets for substituting technology-specific components for predetermined patterns of said hardware components, said first hardware transformation set resulting in fewer components than said second hardware transformation set and said second hardware transformation set resulting in higher-speed logic than said first hardware transformation set.