[riot-devel] RIOT OS port for the icoBoard FPGA board - icoSoC / picorv32 RISC-V platform

Tomas Styblo tstyblo at gmail.com
Sat Sep 12 23:41:23 CEST 2020


Hi Koen,
thank you for checking it out.

All the Verilog code for the CPU and the SoC peripherals is at:

https://github.com/cliffordwolf/picorv32
https://github.com/cliffordwolf/icotools/tree/master/icosoc

The schematics for the board are available. The Lattice FPGA chip and the
auxiliary ICs (FTDI,SRAM,FLASH) are of course proprietary.

On the software side the only problem is that it is difficult to configure
the PLL clock generator without using values provided by the proprietary
Lattice iceCube software. I have not found any open source tool for that,
and the official documentation does not say much about it unfortunately.

I've already made some additions to the SoC code (RX interrupts for the
console and serial UARTS and other things) so it is necessary to patch the
icoSoC code with the patch linked in the RIOT-icoboard documentation. That
also provides a common configuration for testing.

Integrating it all in a user-friendly way is actually the most difficult
part of the project.

The basic picorv32 + icoSoC configuration that I'm using (no MUL/DIV, 20
MHz) needs about 5K LUTS, so there are plenty of free cells for custom
peripherals created in Verilog.

IOs          82 / 206
GBs          1 / 8
GB_IOs     0 / 8
LCs          4565 / 7680
  DFF        1298
  CARRY      521
  CARRY, DFF 140
  DFF PASS   582
  CARRY PASS 106
BRAMs        18 / 32
WARMBOOTs    0 / 1
PLLs         1 / 2

Regards,
--
Tomas Styblo


On Wed, 9 Sep 2020 at 14:11, Koen Zandberg <koen at bergzand.net> wrote:

> Hi Tomas,
>
> On 03-09-2020 21:04, Tomas Styblo wrote:
> > Hi guys,
> > so far it's only an experiment, but I've started porting RIOT OS to
> > the icoBoard Lattice FPGA / icoSoC / picorv32 RISC-V softcore CPU
> > platform.
> >
> > The Lattice chip used on the icoBoard is probably the only FPGA device
> > supported by open source tools. And it will be the first FPGA device
> > supported by RIOT OS (AFAIK)
>
> I think you're right with this. I haven't heard of anybody running RIOT
> on an FPGA softcore before. Doesn't mean that they don't exist of course :)
>
> >
> > RIOT OS already supports the HiFive E310 RISC-V MCU, but that is a
> > very different piece of hardware with RISC-V Privileged Architecture
> > support. Still I've been able to reuse some code chunks.
> I happen to be working on refactoring the fe310 code to split out the
> common RISC-V code bits. Mainly to support the gd32vf103 devices from
> Gigadevice, but any RISC-V MCU should benefit from this. It should at
> least simplify your porting work in the future.
> >
> > So far It's only an experiment (and I'm a newbie at this!), but all
> > the important features already work, including shell over UART. It is
> > really fascinating to be able to use a tiny FPGA board this way.
> (Personally) I think this makes for a great addition to RIOT. Support
> for a softcore really opens a lot of options for designers.
> >
> > If you are interested, you can find the (alpha, experimental!) code at:
> >
> > https://github.com/tstyblo/RIOT-icoboard
> >
> > It would make no sense trying to merge it into the mainline now, as
> > the code needs a lot of testing, comments and improvements. But I'd
> > like to use this opportunity to invite anyone interested in FPGA
> > devices or in the RISC-V platform to check it out.
>
> Looks awesome, thanks for sharing. Is there also a repository with the
> verilog for the FPGA configuration? Any estimation how many LUT's and
> other resources it requires from the FPGA?
>
> Best regards,
>
> Koen Zandberg
>
>
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