Introduction to Silicon Programming in the Tangram/Haste language

1
Introduction to Silicon Programmingin the
Tangram/Haste language

• Material adapted from lectures by
• Prof.dr.ir Kees van Berkel
• Dr. Johan Lukkien
• Dr.ir. Ad Peeters
• at the Technical University of Eindhoven, the
  Netherlands

2
Handshake signaling and data
push channel versus pull channel
request ar
3
Handshake signaling push channel
req ar
ack ak
early ad
broad ad
late ad
4
Data bundling

• In order to maintain event ordering at both sides
  of a channel, the circuit must satisfy data
  bundling constraint
• for push channel delay along request wire must
  exceed delay of data wire
• for pull channel delay along acknowledge wire
  must exceed delay of data wire.

5
Handshake signaling pull channel

• When data wires are invalid multiple and
  incomplete transitions allowed.

req ar
ack ak
early ad
broad ad
late ad
6
Tangram assignment x f(y,z)
Handshake circuit
7
Four-phase data transfer
?r / br
ba / cr
ca / ?a
bd / cd
1 2 3 4 5
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Handshake latch

• ? w?? w?? rd wd r??
  r??
• 1-bit handshake latch wd ? wr ? rd ?
  ?wd ? wr ? rd ? wk wr rk
  rr

9
N-bit handshake latch

• area, delay, energy
• area 2(N1) gate eqs.
• delay per cycle 4 gate delays
• energy per write cycle 4 0.52N
  transitions, in average

10
Transferrer

• ? a?? (b?? c??) a??
  (b?? cd bd c?? cd ?)

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Multiplexer

• ? a?? c?? a?? (cd ad c?? cd
  ?) b?? c?? b?? (cd bd c?? cd
  ?)
• Restriction ?ar ? ?br must hold at all times!

12
Multiplexer realization
control circuit
data circuit
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Logic/arithmetic operator

• ? a?? (b?? c??) a?? ((b??
  c??) ad f(bd , cd ))
• Cheaper realization (delay sensitive)
• ? a?? (b?? c??) a?? ((b??
  c??) ad f(bd , cd )) delay ad
  ?

14
A one-place fifo buffer
byte type 0..255 BUF1 main
proc(a?chan byte b!chan byte).begin x var
byte forever do a?x b!x odend
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A one-place fifo buffer
byte type 0..255 BUF1 main
proc(a?chan byte b!chan byte).begin x var
byte forever do a?x b!x odend
?
a
x
b
x
16
2-place buffer

• byte type 0..255
• BUF1 proc (a?chan byte b!chan byte).begin
  x var byte forever do a?x b!x od end
• BUF2 main proc (a?chan byte c!chan
  byte).begin b chan byte BUF1(a,b)
  BUF1(b,c) end

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Two-place ripple buffer
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Two-place wagging buffer
byte type 0..255 wag2 main
proc(a?chan byte b!chan byte).begin x,y
var byte a?x forever do (a?y
b!x) (a?x b!y) odend
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Two-place ripple register
begin x0, x1 var byte forever do b!x1
x1x0 a?x0 odend
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4-place ripple register

• byte type 0..255 rip4 main proc
  (a?chan byte b!chan byte). begin x0,
  x1, x2, x3 var byte forever do b!x3
  x3x2 x2x1 x1x0 a?x0 od end

21
4-place ripple register

• area N (Avar Aseq )
• cycle time Tc (N1) T
• cycle energy Ec N E

22
Introducing vacancies

• begin x0, x1, x2, x3, v var byte
  forever do (b!x3 x3x2 x2v) (vx1
  x1x0 a?x0) odend
• what is wrong?

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Introducing vacancies

• forever do ((b!x3 x3x2) (vx1
  x1x0 a?x0)) x2v od
• or
• forever do ((b!x3 x3x2) (vx1
  x1x0)) (x2v a?x0)od

24
synchronous 4-p ripple register

• forever do (s0m0 s1m1 s2m2
  b!m3 ) ( a?m0 m1s0 m2s1
  m3s2)od

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4-place wagging register

• forever do b!x1 x1x0 a?x0 b!y1
  y1y0 a?y0od

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8-place register

• 4-way wagging
• forever do b!u1 u1u0 a?u0 b!v1
  v1v0 a?v0 b!x1 x1x0 a?x0 b!y1
  y1y0 a?y0od

27
Four 8?8 shift registers compared
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Tangram/Haste

• Purpose programming language for asynchronous
  VLSI circuits.
• Creator Tangram team _at_ Philips Research Labs
  (proto-Tangram 1986 release 2 in 1998).
• Inspiration Hoares CSP, Dijkstras GCL.
• Lectures no formal introduction manual hand-out
  (learn by example, learn by doing).
• Main tools compiler, analyzer, simulator, viewer.

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2-place buffer

• byte type 0..255
• BUF1 proc (a?chan byte b!chan byte).begin
  x var byte forever do a?x b!x od end
• BUF2 main proc (a?chan byte c!chan
  byte).begin b chan byte BUF1(a,b)
  BUF1(b,c) end

30
Median filter

• median main proc (a? chan W b! chan W).
  begin x,y,z var W xy, yz, zw var bool
  forever do ((zy yx) yzxy)
  a?x (xy xlty zx zltx) if zxxy
  then b!x or xyyz then b!y or yzzx
  then b!z fi odend

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Greatest Common Divisor

• gcd main proc (ab?chan ltltbyte,bytegtgt c!chan
  byte).begin x,y var byte forever do
  ab?ltltx,ygtgt do xlty then y y-x or xgty
  then x x-y od c!x odend

32
Nacking Arbiter

• nack main proc (a?chan bool b!chan
  bool).begin na,nb var bool ltltna,nbgtgt
  ltlttrue,truegtgt forever do sel probe(a) then
  a!nb na nanb or probe(b) then b!na
  nb nbna les od end

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C Tangram ? handshake circuit
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C Tangram ? handshake circuit
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C Tangram ? handshake circuit
C (RS)
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Tangram Compilation
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VLSI programming of asynchronous circuits
behavior, area, time, energy, test coverage
Tangram program
feedback
compiler
simulator
Handshake circuit
expander
Asynchronous circuit
(netlist of gates)
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Tangram tool box

• Let Rlin4.tg be a Tangram program
• htcomp -B Rlin4
• compiles Rlin4.tg into Rlin4.hcl, a handshake
  circuit
• htmap Rlin4
• produces Rlin4.v files, a CMOS standard-cell
  circuit
• htsim Rlin4 a b
• executes Rlin4.hcl with files a, b for
  input/output
• htview Rlin4
• provides interactive viewing of simulation results

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Tangram program Conway
P
Q
R
a
b
c
d

• B1 type 0..1 B2 type ltltB1,B1gtgt
  B3 type ltltB1,B1,B1gtgt P Q
  R conway main proc (a?chan B2
  d!chan B3). begin b,c chan B1 P(a,b)
  Q(b,c) R(c,d) end

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Tangram program Conway

• P proc(a?chan B2 b!chan B1). begin x var
  B2 forever do a?x b!x.0 b!x.1 od end
• Q proc(b?chan B1 c!chan B1). begin y var
  B1 forever do b?y c!y od end
• R proc(c?chan B1 d!chan B3). begin x,y,z
  var B1 forever do c?x c?y c?z d!ltltx,y,zgtgt
  od end

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VLSI programming for

• Low costs
• introduce resource sharing.
• Low delay (high throughput)
• introduce parallelism.
• Low energy (low power)
• reduce activity

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VLSI programming for low costs

• Keep it simple!!
• Introduce resource sharing commands, auxiliary
  variables, expressions, operators.
• Enable resource sharing, by
• reducing parallelism
• making similar commands equal

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Command sharing
P proc(). S P() P()

• S S

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Command sharing example
ax proc(). a?x ax() ax()

• a?x a?x

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Procedure definition vs declaration

• Procedure definition P proc (). S
• provides a textual shorthand (expansion)
• each call generates copy of resource, i.e. no
  sharing
• Procedure declaration P proc (). S
• defines a sharable resource
• each call generates access to this resource

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Command sharing

• Applies only to sequentially used commands.
• Saves resources, almost always(i.e. when command
  is more costly than a mixer).
• Impact on delay and energy often favorable.
• Introduced by means of procedure declaration.
• Makes Tangram program less well readable.
  Therefore, apply after program is
  correct sound.
• Should really be applied by compiler.

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Sharing of auxiliary variables

• xE is an auto assignment when E depends on x.
  This is compiled as auxE x aux ,
  where aux is a fresh auxiliary
  variable.
• With multiple auto assignments to x, as in
• xE ... xF
• auxiliary variables can be shared, as in
• auxE aux2x() ... auxF aux2x()
  with aux2x() proc(). xaux

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Expression sharing
f func(). E xf() a!f()

• xE a!E

e0

e1
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Expression sharing

• Applies only to sequentially used expressions.
• Often saves resources, (i.e. when expression is
  more costly than the demultiplexer).
• Introduced by means of function declarations.
• Makes Tangram program less well readable.
  Therefore apply after program is
  correct sound.
• Should really be applied by compiler.

50
Operator sharing

• Consider x0 y0z0 x1 y1z1 .
• Operator can be shared by introducing
• add func(a,b? var T) T. ab
• and applying it as in x0 add(y0, z0)
  x1 add(y1,z1) .

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Operator sharing the costs

• Operator sharing may introduce multiplexers to
  (all) inputs of the operator and a demultiplexer
  to its output.
• This form of sharing only reduces costs when
• operator is expensive,
• some input(s) and/or output are common.

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Operator sharing example

• Consider x yz0 x yz1 .
• Operator can be shared by introducingadd2y
  proc(b? var T). xyb
• and applying it as inadd2y(z0) add2y(z1) .

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Greatest Common Divisor

• gcd main proc (ab?chan ltltbyte,bytegtgt c!chan
  byte).begin x,y var byte forever do
  ab?ltltx,ygtgt do xlty then y y-x or
  xgty then x x-y od c!x odend

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Assigment make GCD smaller

• Both assignments (y y-x and x x-y) are auto
  assignments and hence require an auxiliary
  variable.
• Program requires 4 arithmetic resources (twice lt
  and ) .
• Reduce costs of GCD by saving on auxiliary
  variables and arithmetic resources. (Beware the
  costs of multiplexing!)
• Use of ff variables not allowed for this
  exercise.