Algebra of Parameterised Graphs
description
Transcript of Algebra of Parameterised Graphs
Andrey Mokhov, Victor KhomenkoArseniy Alekseyev, Alex Yakovlev
Algebra of Parameterised Graphs
MotivationDesign cost is the greatest threat to the semiconductors
roadmap:manufacturing takes weeks, with low uncertaintydesign takes months or years, with high uncertainty
Designer has to explore a large design space, and thus comprehend a huge number ofsystem configurationsoperational modesbehavioural scenariosimplementation choices
Infeasible to consider each individual mode, need toexploit similarities between the individual modeswork with groups of modes rather than individual onesmanage the modes and groups of modes compositionallytransform/optimise specs in a formal and natural way
Design productivity gap
10000py
Annual productivity gain ~20%
Annual man
ufacturin
g gain
>40%
850py“Productivity gap”
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13 lines270 stations
Individual descriptions
• Easier for comprehension and reasoning• Gives bigger picture of the system• Easier to modify than individual lines
OrangePark
Overlaid descriptions
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Characteristics of components
a) 2-input adderb) 3-input adderc) 2-input multiplierd) fast 2-input multipliere) dedicated DP3 unit
Design space exploration
DP3(x,y)=x1y1 + x2y2 + x3y3
Fastest
Design space exploration2 multipliers
Least peak power Dedicatedcomponent
Balanced
Operations on graphs: overlay G1+G2
+
=
=
+
Operations on graphs: sequence G1G2
=
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Operations on graphs: condition [x]G[0]G= (empty graph)[1]G=G
From arithmetic to algebra: use parameters [x]G
Operations on graphs: condition [x]G[0]G= (empty graph)[1]G=G
From arithmetic to algebra: use parameters [x]G
Operations on graphs: condition [x]G[0]G= (empty graph)[1]G=G
From arithmetic to algebra: use parameters [x]G
[1]
[0]
? [x]
Canonical form of PGsProposition: Any PG can be rewritten in the following canonical form:
whereV is a subset of singleton graphs that appear in the original PGbv are canonical forms of Boolean expressionsbuv are canonical forms of Boolean expressions, s.t. buv b⇒ ubv
Algebra of PGsWe define the equivalence relation on PGs abstractly,
using the following axioms:+ is commutative and associative is associative is a left and right identity of left- and right-distributes over +Decomposition: p q r = p q + p r + q rCondition: [0]p = and [1]p = p
Theorem: The set of axioms of PG-algebra is soundminimalcomplete w.r.t. PGs
Useful equalities (proved from axioms) is an identity of ++ is idempotent Left/right absorption:
p + p q = p qq + p q = p q
Conditional : [x] = Conditional + and :
[x](p + q) = [x]p + [x]q[x](p q) = [x]p [x]q
AND-condition: [x y]p = [x][y]p OR-condition: [x y]p = [x]p + [y]p
Case study: phase encoderPhase encoding: data is encoded by the order of arrival
of signals on n wires:
Goal: synthesise matrix phase encoderInputs: dual-rail ports xij that specify the order of
signalsOutputs: phase encoded data vi
abdc
n! scenarios
Case study: phase encoderOverall specification: where Hij models behaviour of
ith and jth output wiresIf xij=1 and xji=0 then there is a causal dependency vi vjIf xij=0 and xji=1 then there is a causal dependency vj viIf xij=xji=0 then neither vi nor vj can be produced yet; this is
expressed by a circular wait condition between vi and vj
|H| and the resulting circuit are linear in the size of input!
Transitive Parameterised Graphs is often interpreted as causal dependency, so the
graphs are transitiveHence two graphs are considered equal iff their transitive
closures are equalCan express this by an additional axiom Closure:
if q then p q + q r = p q + p r + q rOften allows to simplify expressions by transitive
reduction
Transitive parameterised graphs
PG expression [x]((a + b)c + cd) + [x]((a + b)(d + e))with the specialisations
TPG expression (a + b)([x]cd + [x]e)with the specialisations
Canonical form of TPGsProposition: Any TPG can be rewritten in the following canonical form:
whereV is a subset of singleton graphs that appear in the original TPGbv are canonical forms of Boolean expressionsbuv are canonical forms of Boolean expressions, s.t. buv b⇒ ubv
transitivity: for all u,v,w V, b∈ uv bvw b⇒ uw
TPG axioms – minimal, sound, completeTheorem: The set of axioms of TPG-algebra is
soundminimalcomplete w.r.t. TPGs.
Case study: Processor microcontroller
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Case study: Processor microcontroller
Instructions classes:ALU Rn to Rn e.g. ADD A,B; MOV A,BALU #123 to Rn e.g. SUB A,#1; MOV
B,#3ALU Rn to PC e.g. JMP AALU #123 to PC e.g. JMP #2012Memory access e.g. MOV A,[B]; MOV
[B],ACond. ALU Rn to Rn e.g. if A<B then ADD A,BCond. ALU #123 to Rn e.g. if A<B then SUB A,#1Cond. ALU #123 to PC e.g. if A<B then JMP #2012
Case study: Processor microcontrollerALU #123 to Rn e.g. SUB A,#1; MOV B,#3TPG algebra specification:
PCIU IFU (ALU + PCIU’) IFU’The graph is considered up to transitivity
Case study: Processor microcontrollerCond. ALU #123 to Rn e.g. if A<B then SUB A,#1If A < B holds:
(ALU + PCIU) IFU (ALU’ + PCIU’) IFU’If A < B does not hold:
(ALU + PCIU) PCIU’ IFU’Composing the two scenarios, lt := (A<B):
[lt]((ALU + PCIU) IFU (ALU’ + PCIU’) IFU’)+[lt]((ALU + PCIU) PCIU’ IFU’)
=(ALU + PCIU) [lt]IFU (PCIU’ + [lt]ALU’) IFU’
Case study: Processor microcontrollerCond. ALU #123 to Rn e.g. if A<B then SUB A,#1
(ALU + PCIU) [lt]IFU (PCIU’ + [lt]ALU’) IFU’
Case study: Processor microcontroller
Case study: Processor microcontroller
Conclusions and future workNew formalisms: PG and TPG algebrae with sound,
minimal and complete sets of axiomsCanonical formsCan work with groups of scenarios and exploit the
similarities between themCan formally compose, manipulate and simplify the
specifications using the rules of these algebraeApplications in microelectronics, formal methods,
computer architecture, modelling university courses
Future work:Tool implementationSimplification by modular decomposition of graphs
Thank you!