[lowrisc-dev] Re: Question on lowrisc project

Pawan Reddy Sibbala ps849 at cornell.edu
Mon Feb 15 15:54:39 GMT 2016

Hello Wei,

I have two questions that I'd like to ask you.

1. The rocket core on the zedboard FPGA  currently runs at 25Hz. Could you
tell me the maximum frequency at which it can run ? I was wondering if you
already experimented with the parameters in "clocking.vh" to find the
maximum frequency.

2. Does the new release of the untethered version of the rocketchip use a
opensource IP for implementing the Memory Controller or does it use the
Xilinx IP?

Thanks and regards,

On Mon, Feb 8, 2016 at 5:41 AM, Wei Song <ws327 at cam.ac.uk> wrote:

> Hello Pawan,
> This is a legacy issue.
> In short, No. The tagged memory release does not support L2$ although
> the Config option is there.
> It was found that with L2$ enabled, a coherence bug in L2$ will cause
> issues in running SPEC, not mention booting a Linux.
> Internally, I did fix the bug which allowed SPEC but failed to find the
> problem with booting Linux.
> For the following months Berkeley has gradually fixed bugs.
> However, since the Rocket-chip has numerous updates that are not
> directly compatible with the old release, there is no hope to make the
> old release working withing with L2$.
> The new untethered release has L2$ in default but currently without
> tagged memory support.
> We plan to re-integrated an expanded tag support later this year.
> Best regards,
> Wei
> On 07/02/2016 06:27, Pawan Reddy Sibbala wrote:
> > Hello Wei,
> >
> > I have a question about the memory hierarchy of the rocket chip
> > configured on the zedboard FPGA.  Does the prebuilt FPGA image of the
> > rocket chip for zedboard have an L2 $ cache configured? In the
> > zedboard/src/verilog folder, I see that it DefaultFPGAConfig.v. From
> > the "Configs.scala" file, I see that L2 $ is not included in the
> > DefaultFPGAConfig setting. So, I think there is no L2$ configured in
> > the prebuilt image. Am I correct?
> >
> > http://wsong83.github.io/publication/comparch/riscv2015.pdf
> >
> > But in the above paper, your configuration also has 128KB L2$. Did you
> > use different configuration settings to include the L2 $?
> >
> > Thanks and regards,
> > Pawan
> >

Pawan Reddy Sibbala
Cornell University

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