[J-core] Online talk on the 16th.

[Tim 'mithro' Ansell]

I haven't had a chance to watch your talk yet but I wanted to mention that
LiteDRAM can do DDR3 on Spartan 6 FPGAs (and handles all the multi-clocks
and clock domain crossing stuff for you). You can even use LiteDRAM as a
module inside your VHDL -- microwatt is already doing this @
https://github.com/antonblanchard/microwatt

LiteDRAM *also* supports DDR, DDR2 and LPDDR2 on the Spartan 6.

There is also a bunch of current work in LiteDRAM lately to improve
performance with multi-core RISC-V systems --
https://github.com/enjoy-digital/litedram/issues/209

We will be looking at using LiteDRAM with an open source ASIC DFI
implementation on SKY130 in the near future.

Tim 'mithro' Ansell

On Mon, 27 Jul 2020 at 21:52, Rob Landley <rob at landley.net> wrote:

> Brian Bartholomew wrote:
> >  >
> https://www.youtube.com/watch?v=dVD1Yws__v0&list=PLxde5XJWZRbTerLRlh0vp43scTA3cfKN8
> >
> > I watched the talks, and the progress ie exciting; I didn't know DDR3
> > and ethernet were already implemented.
>
> 100baseT ethernet and LPDDR2 controller have been implemented for a while.
> Gigabit isn't too hard if you're ok talking to an off the shelf PHY chip.
> DDR3
> controllers are available as a library in some FPGAs we're using, but we
> need to
> do our own implementation that we can make an ASIC out of.
>
> The problem with DDR3 and gigabit ethernet is is clocking the I/O fast
> enough.
> We're trying to deploy stuff in cheap FPGAs you can get in bulk for under
> $50.
> There are fast expensive FPGAs that cost 10 times that, and we have a few
> for
> development, but it's too expensive to deploy anything in, where deploy
> means
> "send to customers" or "expect a larger development community to use".)
>
> In theory you can have I/O circuitry at the edge of the FPGA clocked way
> faster
> than the processor the rest of it's implementing, but then there's clock
> routing
> and domain crossing, and still timing closure, and the result's messy. We
> added
> a clock domain crossing for the GPS correlators on spartan 6 (which isn't
> as
> fast as kintex so going at the CPU speed it could only track 3 satellites
> at
> once and we needed 5) and it took weeks to debug.
>
> In the current SOC, 100baseT is 11 megabytes/second (benchmarked) and SD
> 1.0 is
> 12.5 megabytes/second (before packet overhead anyway, 4 data wires clocked
> at 25
> mhz) and when things match up like that switching just _one_ part to be
> faster
> leaves the fast bit spinning its wheels. There's a certain amount of
> needing to
> upgrade multiple parts at once to reach a new balance.
>
> > But where can I buy all that
> > hardware you featured?
> >
> > Brian
>
> In theory it's going up on crowdsupply. Mike Tokue (in Tokyo) is handling
> that.
>
> Rob
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