Download Lecture 8

VLSI Programming of
Asynchronous circuits for Low
Power
Kees van Berkel
Philips Research Lab.
Martin Rem
Eindhoven University of Technology
Tangram:
• Tool name: Tangram
• CMOS dissipates when active
• The power consumption = the amount of activity.
• Energy consumption:  Ni 1CiVdd  1 C Vdd  Ni
2
2
2
2
L
i
i
where Ni : # of output transition s on gate i
Ci : the load capcitance of gate i
C L : the average load capacitanc e
Vdd : supply voltage
• To reduce the energy consumption of ICs:
A. reduce the energy consumption per transition
B. reduce the number of transitions
Tangram:
An ancient Chinese game that is
also known as "the wisdom puzzle".
Tangram:
• Tangram programs contain 4-p HS components.
• Think two-phase build four-phase
• HS components are connected through channels
• Channel has two ports.
A. active port (signal a request).
B. passive port (respond an ack).
• Channel has two wires: Xreq and Xack.
• Note that for CMOS
0-->1 consume power (charge capacitance).
1-->0 discharge the capacitance.
Basic gate energy
consumption:
• A. Inverter: Einv=1
output =1 when input = 0
1
0
Basic gate energy
consumption:
• B. Nand: Enand=1
1
0
1
• C. And: Eand=2
Basic gate energy
consumption:
• D. Nor : Enor=1
1
0
0
• E. OR: Eor=2
Basic gate energy
consumption:
B
• Another And: Eand=1
A
B
C
0
• Another Or: Eor=1
B
1
B
A
C
Basic gate energy
consumption:
• E: Xor: Exor=2
• F: Xor: Exor=1.5
1
1
A
A'
A
B'
A
B
A'
B'
B'
A
B
C
C
B
A'
A
B
B
B'
0
0
C=1 if A=1 and B=0 or A=0 B=1
B'
Basic gate energy
consumption:
• Xnor: Exnor=1.5
• G: Xnor: Exnor=2
1
1
A
B
A'
B'
A
A'
B
B'
A
B
A
C
A
A'
B'
B'
B
0
C
B
0
B'
Basic gate energy
consumption:
• C-element: Ec=3
• another C-element: Ec=2
1
weak
A
1
1
B
A
C
1
B
C
A
B
C
0
A
B
0
0
Control Handshake
Components
• repeater: control the
a
unbounded repetition of an action.
b
#
passive port Active port
• Sequencer: control the sequential
execution of two actions
b
;*
a
• mixer: provide access to a shared
resource to two parties
a
c
|
b
c
Control Handshake
Components
aa
• repeater: Erep=2
a
#
passive port
b
ba
ar
x
Active port
• initial x=1
A. ar+ ==>x- (inv- +1) ==> br+ (nor+ 1)
B. ba+ ==> br- (nor- 1)
C. ba- ==> br+ (nor+ 1)
D. ba+ ==> br- (nor- 1)
• C and D loop forever.
br
Control Handshake
Components
• sequencer: Eseq=10 ba
b
a
;*
c
• initial x=1 y=0
1
1
x
y
ar
ar
ba
ar
br
ba
0
cr
0
aa
A. ar+ ==> br+ (and+ 2)
B. ba+ ==> x=0 y=1 (invX- invY+ 2) ==> br- (and- 2)
C. ba- ==> cr+ (nor+ 1)
D. ca+ ==> aa+
E. ar- ==> x=1 y=0 (invX+ invY- 2) ==> cr- (nor- 1)
F. ca- ==> aa-
ca
Control Handshake
Components
• mixer (call element): Emix= Ecall= 8
aa
C
a
|
c a
r
br
b
ba
C
• all variables are zero:
A. ar+ ==> cr+ (or+ 2)
B. ca+ ==> aa+ (c-ele+ 2)
C. ar- ==> cr- (or- 2)
D. ca- ==> aa- (c-ele- 2)
ca
cr
ca
Control Handshake
Components
• duplicator: Edup= Eseq + 2Emix =26
a0
#2
a1
;*
a0
|
a1
• 2 m -fold repeater: E2m= 2 m Edup
a0
a0
#2m
#2
am
a1
#2
a2
am-1
#2
am
Control Handshake
Components
• N-fold repeater:
A. N=1 : wire
B. N is even:
N=2*(N/2)
ar
br
aa
ba
a
;*
C. N is odd:
N=1+(N-1)
a
|
;*
|
n-1
b
n/2
b
Control Handshake
Components
• select: Esel = ? (hw)
a
b
d
c
e
[l]
wa
a1
br
ba
C
r1
a
;*
C
dr
da
r2
a2
wb
wd
L
cr
er
ca
ea
Control Handshake
Components
• Parallel : Epar = ?


PAR(a , b , c )  *(ar; (br; ba) || (cr; ca); aa)

a
b
||
c
Datapath Handshake
Components
• Handshake latch:
w
L
r
W0
Q
Q
Wa
read1
Q'
W1
QA1
Q'
QA0
Datapath Handshake
Components
ar aa
• Transfer: Etran=0
a
b
c
T
br
ca
b0
c0
b1
c1
• Simple assignment: Eass=no of bits*(Eread+Ewrite)
a
y.w
L
y.r
r
T
x.w
cL
x.r
Datapath Handshake
Components
• 2-place ripple register:
Tangram Program: proc (a?W & b!W)
r wr
begin
x0,x1: var W
|
forever do b!x1; x1:=x0;a?x0
end
#
;*
;*
x0
a
T
L
x1
r
T
c
L
T
b
Datapath Handshake
Components
• 4-place ripple register:
• n-place ripple register:
a
#
;*
wr
L
r wr
;*
r
T
c
L
T
b
Datapath Handshake
Components
• Adder:
ADD(a  ! Ta, b ?Tb, c ?Tc) 
| [x : Tb, y : Tc
| *(ar; (br; ba(x) || cr; ca(y)); aa(x  y))
]|
b
+
c
a
Datapath Handshake
Components
• Comparator:
b
c
a
&
a
c
• And Operation:
b
c
Handshake Circuit
i
• Addition:
*;
a
r
c
T
L
+
||
b
r
T
c
L
T
c
Handshake Circuit
• Waggin FIFO:
#
wr
a
|
|
*;
r wr
b
Handshake Circuit:
Optimization
• Mixer:
ar+ ==> ca+
ar- ==> ca-
aa
ar
br
ca
ca
aa
ar
br
ar
0
C
ca
C
+
ca
weak
aa
ca
cr
Asymmetric C-element ba
1
C
ba
+
C
cr
ca
Handshake Circuit:
Optimization
• Seq-Mixer
reordering
r1
*;
|
p1
|
p2
r2
*;
r1
|
r2
;*
p1
p2