CS 140 Lecture 16 System Designs

1. CS 140 Lecture 16System Designs Professor CK Cheng CSE Dept. UC San Diego

2. System Designs • Intro • Components • Implementation

3. Implementation: Example Given a hardware program, implement data path and control subsystems { Input X<0:7>, Y<0:7> type bit-vector, start type boolean; Local-Object A<0:7>, B<0:7> type bit-vector; Output Z<0:7> type bit-vector, done type boolean; Wait: If start’ goto Wait; S1: A <= X || B <= Y|| done <= 0; S2: If B >= 0 goto S4; S3: B <= -B; S4: If A >= B goto S6; S5: A <= A + 1 || B <= B-1 || goto S4; S6: Z <= 4 * A || done <= 1 || goto Wait; }

4. 8 X Data Subsystem 8 Z 8 (A > B) Y B7 C1-7 Control Subsystem done start 4 Ceiling[ (X + |Y| )/ 2] if X< |Y| 4X otherwise Z =

5. control C1 C2 C3 C4 C5 C6 C7 operation A  Load (X) B  Load (Y) B  CS (B) Comp (A, B) A  INC (A) B  DEC (B) Z  Load (A) Z  SHL (Z) A  X B  Y B  -B A >= B A  A + 1 B  B – 1 Z  4A

6. CS DEC B Y Z Comp C2 C3 C5 C1 C4 C6 C7 X A Control Unit C1 C2 C3 INC C4 B<7> C5 C6 start C7 done

7. Designing the control unit S0: S1: S2: S3: S4: S5: S6: S7: S8: If start’, goto S0, else goto S1 A  X || B  Y || done  0 || goto S2 If B’<7> goto S4, else goto S3 B  CS (B), goto S4 If k goto S6, else goto S5 A  INC (A), B  DEC (B), goto S4 Z  A goto S7 Z  SHL (z), goto S8 Z  SHL (z), done 1, goto S0

8. State Machine S0 start’ start S1 S8 S2 S7 B’<7> B<7> S6 S3 k k’ S4 S5

9. Control Subsystem: One-Hot State Machine Design • Input: State Diagram • Use a flip flop to replace each state. • Set the flip flop which corresponds to the initial state and reset the rest flip flops. • Use an OR gate to collect all inward edges. • Use a Demux to distribute the outward edges.

10. One-Hot State Machine S8 S0 start’ start S7 S1 S6 S2 B7’ B7 S5 k S3 k’ S4