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Message
From: Bill Cox<bill@v...>
Date: Mon Aug 30 18:33:13 CEST 2004
Subject: [oc] Parallel Array Processor Project
Hi.I've actually done a bit of work on what I called "Parallel Data Path
Arrays", or PDPAs for short. The comunication was all with 8-bit
busses, not serial, so it's not a direct comparison.
The thought was that it would make a good candidate for an SBIR (small
business inovation research grant). However, I hate wasting taxpayer
money, and after the initial research turned out poorly, I killed the
project.
What I remember about PDPAs vs. FPGAs:
- Routing dominates both. The actual computation elements are a small
percentage of either (< 25% area). Basically, an FPGA is mostly routing
switches.
- Control logic still has to be implemented, and so an FPGA-like fabric
needs to be included in the PDPA.
- The ratio of area devoted to the FPGA like fabric vs the PDPA fabric
was around 1:1.
Basically, unless an application used a lot of datapaths, and not much
random logic, it was a poor fit for a PDPA. However, that's OK. But it
got worse when I started doing more comparisons.
The basic problem was that each bit of each bus still needed to go
through a complex routing fabric to get to a destination. The routing
fabric for the PDPA was smaller than that used in an FPGA, but by less
than about 2x in area. Even using 8-bit buses didn't help much, since
we still needed individual networks of switches for each bit, and the
control logic for Xilinx's switches takes up a small fraction of the
total area devoted to routing.
I was unable to get the PDPA fabric down to 1/2 the area of an FPGA for
any realistic class of applications. Even if I had, a factor of 2 isn't
enough to both spending money trying to compete against Xilinx. I
basically concluded that there isn't any real market for these kinds of
parts.
Bill
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