[J-core] Sorry for the radio silence.

BGB cr88192 at gmail.com
Mon May 15 01:17:33 EDT 2017

On 5/14/2017 11:14 PM, Rob Landley wrote:
> On 05/14/2017 06:12 PM, BGB wrote:
>> yeah, looking into it, it apparently is pretty variable (depends on the
>> type of FPGA and the vendor).
> Think of each FPGA vendor as a different architecture target
> (arm/mips/sh/x86/cris/powerpc/sparc) different toolchains target. And
> each ASIC fab is _also_ a different target. (Moving from 150 to 45
> nanometers at the same company, 2 different 45 nanometer fabs from
> different companies... all different targets with wildly different
> optimization.)
> In theory the tools should handle most of this for you. In practice,
> it's a bunch of different proprietary toolchains, often outright buggy.
> You need all the tests in the world...


>> a lot of them use SRAM (apparently the wiring done mostly with flip-flops).
>> others use FGMOS (like used in Flash), where basically the residual
>> charge held in a MOSFET is used to control whether a connection is
>> open/closed (just it requires driving an elevated voltage to change the
>> state of the MOSFET).
> More patents should expire and advance the FPGA state of the art before
> too long. My understanding is Lattice is least proprietary, but also
> fairly trailing edge in terms of technology (which hits _us_ in terms of
> capacity, the amount of FPGA capacity to emulate an entire processor
> simply wasn't a _thing_ 15 years ago, then became available only at the
> ultra high end, and is finally reasonably priced but only from certain
> vendors and with proprietary tools...)
> There's a fun talk an AMD guy gave a while back about how they can't
> simulate their chip design in even the highest-end FPGAs because it's
> just way too big:
>    https://www.youtube.com/watch?v=eDmv0sDB1Ak&t=52m0s
> Meanwhile, our stuff fits in the cheap low-end FPGAs. :)

yeah; granted, a modern x86 chip is a pretty big complicated thing.

in my own ideas, I am still trying to be relatively conservative.
partly, there is the "could this work in hardware" aspect, but also the 
"would it be worthwhile to bother implementing it".

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