Re: GSoC'16 | JPEG Encoder

Hi all,

> 
> I wrote an inline complex multiplier based around a single DSP which
> really gets into the guts of the DSP core. It's hard to see how one
> would do this in plain VHDL with a hope that it would be inferred
> correctly (the difficulty is in things like flicking control registers
> mid pipeline from multiply-add to multiply-accumulate to
> multiply-deccumulate).
> 

I never had troubles getting the right thing instanced when staying
below the 18 bit of the classic multiplier primitive. Above that, it can
get funky on some toolchains WRT timing, but the nice thing about MyHDL
is that it allows you to swap out the primitives in a much more
configurable/reusable way than on the VHDL level.
For the pipeline control, I typically use VLIW microcode that can be
adapted easily if one of the MAC primitives needs to use a higher delay
within the pipeline. So on the high level 'synthesis', you spell out the
ops done in the pipeline in Python and the architecture (FPGA vendor)
specific translator rolls out the rest. So a DCT is just a "hardware
applet". If you spell it out in pure (vendor independent) VHDL, the
synth tools always did it right so far, it just wasn't always optimal
for their architecture and this is where the manual optimizations get
nasty and way less reusable than in MyHDL.

Greetings,

- Strubi

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