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CS220 Programming Principles. 프로그래밍의 이해 2002 가을학기 Class 12: Logic Circuit Simulation 한 태숙. Event-driven Simulation. Example: Digital Circuit function box : logic gates wire : connections delay: characteristics Model

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cs220 programming principles

CS220Programming Principles

프로그래밍의 이해 2002 가을학기

Class 12: Logic Circuit Simulation

한 태숙

event driven simulation
Event-driven Simulation
  • Example: Digital Circuit
    • function box : logic gates
    • wire : connections
    • delay: characteristics
  • Model
    • wire : computational objects which “hold” the signals -> make-wire
    • function boxes : procedure that enforce the correct relationships among signals
half adder
Half Adder

(define a (make-wire))

(define b (make-wire))

(define d (make-wire))

(or-gate a b d)







half adder1

(define (half-adder a b s c)

(let ((d (make-wire)) (e (make-wire)))

(or-gate a b d)

(and-gate a b c)

(inverter c e)

(and-gate d e s)


full adder
Full Adder

(define (full-adder a b c-in sum c-out)

(let ((s (make-wire))

(c1 (make-wire))

(c2 (make-wire)))

(half-adder b c-in s c1)

(half-adder a s sum c2)

(or-gate c1 c2 c-out)


wire delay
Wire + Delay
  • Constructor : (make-wire)
  • (get-signal <wire>)
    • returns the current value of the signal on the wire
  • (set-signal! <wire> <new-value>)
    • changes the value of the signal on the wire
  • (add-action! <wire> <procedure of no args>)
    • asserts that the designated procedure should be run whenever the signal on the wire changes value
  • after-delay : simulates propagation delay
gate not
Gate Not

(define (inverter input output)

(define (invert-input)

(let ((new-value (logical-not (get-signal input))))

(after-delay inverter-delay

(lambda ()

(set-signal! output new-value)))))

(add-action! input invert-input)


(define (logical-not s)

(cond ((= s 0) 1)

((= s 1) 0)

(else (error "Invalid signal" s))))

gate and
Gate AND

(define (and-gate a1 a2 output)

(define (and-action-procedure)

(let ((new-value

(logical-and (get-signal a1)(get-signal a2))))

(after-delay and-gate-delay

(lambda ()

(set-signal! output new-value)))))

(add-action! a1 and-action-procedure)

(add-action! a2 and-action-procedure)


gate or exercise 3 28
Gate OR : exercise 3.28

(define (or-gate o1 o2 output)

(define (or-action-procedure)

(let ((new-value

(logical-or (get-signal o1)

(get-signal o2))))

(after-delay or-gate-delay

(lambda ()

(set-signal! output


(add-action! o1 or-action-procedure)

(add-action! o2 or-action-procedure)


logical and logical or
Logical And, Logical Or

(define (logical-and s1 s2)

(cond ((and (= s1 1)(= s2 1)) 1)

((and (= s1 0)(= s2 1)) 0)

((and (= s1 1)(= s2 0)) 0)

((and (= s1 0)(= s2 0)) 0)

(else (error "Invalid signal" s))))

(define (logical-or s1 s2)

(cond ((and (= s1 1)(= s2 1)) 1)

((and (= s1 0)(= s2 1)) 1)

((and (= s1 1)(= s2 0)) 1)

((and (= s1 0)(= s2 0)) 0)

(else (error "Invalid signal" s))))

representing wires
Representing Wires

(define (make-wire)

(let ((signal-value 0) (action-procedures '()))

(define (set-my-signal! new-value)

(if (not (= signal-value new-value))

(begin (set! signal-value new-value)

(call-each action-procedures))


(define (accept-action-procedure! proc)

(set! action-procedures

(cons proc action-procedures))


(define (dispatch m)

(cond ((eq? m 'get-signal) signal-value)

((eq? m 'set-signal!) set-my-signal!)

((eq? m 'add-action!)



(error "Unknown operation --WIRE" m))))


(define (call-each procedures)

(if (null? procedures)



((car procedures))

(call-each (cdr procedures)))))

(define (get-signal wire)

(wire 'get-signal))

(define (set-signal! wire new-value)

((wire 'set-signal!) new-value))

(define (add-action! wire action-procedure)

((wire 'add-action!) action-procedure))

the agenda
The Agenda
  • (make-agenda)
    • constructor: returns a new empty agenda
  • (empty-agenda? <agenda>)
    • is true if the specified agenda is empty
  • (first-agenda-item <agenda>)
    • returns the first item on the agenda
  • (remove-first-agenda-item! <agenda>)
    • modifies the agenda by removing the first item
  • (add-to-agenda! <time> <action> <agenda>)
    • modifies the agenda by adding the given action procedure to be run at the specified time
implementing delay after delay
Implementing Delay: After-delay
  • (current-time <agenda>)
    • return the current simulation time
  • We will define the-agenda as agenda data structure

(define (after-delay delay action)

(add-to-agenda! (+ delay (current-time




driver program propagate
Driver Program - Propagate

(define (propagate)

(if (empty-agenda? the-agenda)


(let ((first-item

(first-agenda-item the-agenda)))





probe detecting signal
Probe - Detecting Signal

(define (probe name wire)

(add-action! wire

(lambda () (newline)

(display name)

(display ” ”)

(display (current-time


(display ” New-value= ”)

(display (get-signal


setting up environment
Setting Up Environment

(define the-agenda (make-agenda))

(define inverter-delay 2)

(define and-gate-delay 3)

(define or-gate-delay 5)

; circuit description

(define input-1 (make-wire))

(define input-2 (make-wire))

(define sum (make-wire))

(define carry (make-wire))

(probe 'sum sum)

(probe 'carry carry)

(half-adder input-1 input-2 sum carry)

running the simulation
Running the simulation

> (set-signal! input-1 1)


> (propagate)

sum 8 New-value = 1


> (set-signal! input-2 1)


> (propagate)

carry 11 New-value = 1

sum 16 New-value = 0


implementing agenda i
Implementing Agenda(I)

(define (make-time-segment time queue)

(cons time queue))

(define (segment-time s) (car s))

(define (segment-queue s) (cdr s))

(define (make-agenda) (list 0))

(define (current-time agenda) (car agenda))

(define (set-current-time! agenda time)

(set-car! agenda time))

(define (segments agenda) (cdr agenda))

(define (set-segments! agenda segments)

(set-cdr! agenda segments))

(define (first-segment agenda) (car (segments agenda)))

(define (rest-segments agenda) (cdr (segments agenda)))

implementing agenda ii
Implementing Agenda(II)

(define (empty-agenda? agenda)

(null? (segments agenda)))

(define (remove-first-agenda-item! agenda)

(let ((q (segment-queue (first-segment agenda))))

(delete-queue! q)

(if (empty-queue? q)

(set-segments! agenda (rest-segments agenda)))))

(define (first-agenda-item agenda)

(if (empty-agenda? agenda)

(error "Agenda is empty -- FIRST-AGENDA-ITEM")

(let ((first-seg (first-segment agenda)))

(set-current-time! agenda

(segment-time first-seg))

(front-queue (segment-queue first-seg)))))

implementing agenda iii
Implementing Agenda(III)

(define (add-to-agenda! time action agenda)

(define (belongs-before? segments)

(or (null? segments)

(< time (segment-time (car segments)))))

(define (make-new-time-segment time action)

(let ((q (make-queue)))

(insert-queue! q action)

(make-time-segment time q)))

(define (add-to-segments! segments)

(if (= (segment-time (car segments)) time)

(insert-queue! (segment-queue (car segments))


(let ((rest (cdr segments)))

(if (belongs-before? rest)



(cons (make-new-time-segment time action)

(cdr segments)))

(add-to-segments! rest)))))

(let ((segments (segments agenda)))

(if (belongs-before? segments)



(cons (make-new-time-segment time action)


(add-to-segments! segments))))