For accelerationg computation-intensive applications FPGAs are not sufficient.
Word-level parallelism is needed (fig. 1) instead
of the bit-level parallelism by FPGAs being available commercially. Rainer
Kress has implemented such a word level FPAA (field-programmable ALU Array)
 . His first generation
FPAA, which he called rDPA (reconfigurable Data Path Array), is an array
of 32 Bit ALUs. Fig. 3 illustrates its
programmability. To obtain area-efficiency only horizontal or vertical
direct neighbor ALUs can be connected directly (fig.
2). Tow links are available for non-multiplexed bidirectional links
(fig. 2). A single bus reaching all ALUs
is needed for configuration programming. This bus may also give some flexibility
by run time usage.
Fig. 4 illustrates Kress Array Technology
mapping. Left side shows an 8 equations problem example. The right side
of the figure shows the routing and placement result obtained for the 1st
generation Kress array (only a single unidirectional link between nearest
neighbors). Routing and placement is done by a simple simulated annealing
optimizer DPSS having been implemented by Rainer Kress and his students
. The DPSS (data path synthesis system) is
fast and needs only a few seconds on a SPARC station.
DPSS has been integrated into an application development support environment Co-De-X for the Kress Machine, having been dimplemented for the Kress Machine (a MoM Xputer architecture). Co-De-X  accepts problem descriptions C-X language source text. C-X is an extension of the programming language C. The Co-De-X environment includes 2 levels of automatic partitioning: (1) host/accelerator partitioning based on ressource parameters, and, (2) (data-)procedural/structural partitioning for FPAA configuration and data sequencer programming.
A number of very much promising acceleration
factors have been obtained from Xputer research. Will work stations
become obsolete? The same and even much higher performance may be obtained
by a PC with a universal FPAA-based programmable accelerator - on board
of the processor chip. For a wide variety of applications, like in DSP,
image processing, scientific computing, and multi media applications substantially
to drastically higher speed-up is obtained with a Kress-Array-based accelerator
than by using caches. The highly regular Kress array is suitable for full
custom design, where short wires permit high performance with low power.
Such a design should better to be done by microprocessor designers, since
FPGA designers are not well qualified for such a project.
|8eq Eight Equations Example||8eq Example mapped onto rDPA (recongifurable Data Path Arrtay)|
y10 := a0 * (b0 + 2 * c0);
y20 := 5 * d0 + e0 + (f0 + b0):
y30 := g0 * (h0 + 2 * e0);
y40 := (5 * d0 + e0) * f0;
y11 := a1 * (y10 + 2 * c1);
y21 := 5 * y20 + e1 + (f1 + y10):
y31 ;= y30 * (y40 + 2 * e1);
y41 := (5 * y20 + e1) * f1;
In this example the utilization is about 70%, since 23 from 32 rALUs
are used (fig. 4). This is a quite
good result, compared to FPGAs available commercially, which often show
a routability hardly higher than 50% or even below. Because of the massive
obtained by Kress Array use even much lower routability results would be
A highly promising very powerful novel technology platform for software-only accelerator implementation has been introduced , along with a new compilation method accepting C sources .
 R. Kress: A fast reconfigurable ALU for
Xputers; Ph. D. dissertation, Kaiserslautern University, 1996
 R. Hartenstein, R. Kress: A Datapath Synthesis System for the Reconfigurable Datapath Architecture; Proc. Asia and South Pacific Design Automation Conference (ASP-DAC'95), Makuhari, Chiba, Japan, Aug. 29 - Sept 1, 1995
 R. Hartenstein, J. Becker, M. Herz, U. Nageldinger: A General Approach in System Design Integrating Reconfigurable Acclerators; IEEE Int'l Symp. on Innovative Systems (ISIS'96), Austin, Texas, 9-11 Oct. 1996
 R. Hartenstein, J. Becker: A Two-level Co-Design Framework for data-driven Xputer-based Accelerators; Proc. 30th Hawaii Int'l Conf. on Systems Sciences (HICSS-30), Wailea, Maui, Hawaii, Jan. 7 - 10, 1997
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