From: ptkwt@... (Phil Tomson)
Date: 2006-02-03T10:33:18+09:00
Subject: Re: neuroimage software - scientific computing and visualization

In article <43E29027.9090908@path.berkeley.edu>,
Joel VanderWerf  <vjoel@path.berkeley.edu> wrote:
>Phil Tomson wrote:
>> Here's an tantalizing idea that I'll throw out:  C is one thing and, yes, it's 
>> fast.... but what if you could actually map some algorithm or math operation to 
>> _hardware_ and thus get a large speed  advantage even over C?  I'm working on 
>> something like this... details forthcoming.  The idea is very similar to 
>> Ruby::Inline.  It will allow seamless communication between your Ruby program 
>> and an FPGA board acting as hardware accelerator (these boards are available 
>> for less than $200 now).
>
>That would be very cool. Eventually, we're going to be porting a
>wireless network stack to FPGA, and being able to still use Ruby would
>be very nice.
>
>What kind of code goes inside your "inline" blocks?
>

Initially it's going to be VHDL, a hardware description language.  There are 
lots of efforts afoot to use C and a hardware description language, but I'm 
just not sure yet that there's much advantage (YET) over using an HDL like 
VHDL.  The semantics of an HDL are much different than the semantics of a 
programming language like C or Ruby.  HDLs have to model the parallelism 
inherant in hardware.  

So the idea of RubyInline::HDL is evolutionary rather than revolutionary: use 
Ruby for what it's good for and use HDLs for what they're good for.  Of course, 
from a practical standpoint, using VHDL also makes it easy to use the free 
(though not open source, unfortuneatly) tools from Xilinx to program their 
FPGAs.

In the future, I'd like to build on RHDL (Ruby as an HDL) so that it can 
generate VHDL as an output.  At that point then the inlined 'language' would 
be RHDL (really a Ruby-based DSL).  Also, at some point it would be good to 
support FpgaC which is an open source C programming environment for FPGAs.

In the short term, you'll either need to know VHDL to use Inline::HDL, or 
perhaps we could build a repository (using gems perhaps?) of useful VHDL 
modules that users could download from some website.  Lots of common DSP 
functions could be made available.  This could make it so that you wouldn't 
have to know much VHDL to use Inline::HDL.

So, for example, say you want to use Ruby to do some image processing.  Maybe 
you want that image processing to be in real time.  Maybe C isn't even fast 
enough for whatever you're doing.  You download some image processing packages 
which are written in VHDL and you inline them using Inline::HDL.  Your system 
would look something like:

camera -> FPGA (running image processing algorithms)->PCI bus->Ruby program

In this scenario the dataflow is pretty much one way, but you can imagine other 
scenarios where your Ruby program sends some data to the FPGA to be processed 
and waits for an answer back.  Maybe you're doing some sort of optimization 
that would take a long time in software, but would be much faster if it can be 
implemented in hardware.  Your Ruby program would send a block of data over the 
PCI bus to the FPGA card, the FPGA card would then process that data and send 
back the processed data.  

RubyInline::HDL would take care of setting up all the interfaces (hardware and 
software) between the Ruby program and the FPGA board and it would take care 
of running the Xilinx tools to create the bitstream (if one doesn't already 
exist).  That's the theory anyway; this is all very preliminary based on some 
work I did last summer using a 
VHDL simulator (ghdl) in place of an FPGA board.   I need to finish that up to 
get testing going and then start working with actual hardware.  Now 
that my Masters degree is about done (defense is tomorrow!) I'll have some time 
to put into this over the next couple of months.

Phil