[lowrisc-dev] Untethered lowRISC 0.2 with Zedboard

Jamey Hicks jamey.hicks at gmail.com
Mon Feb 1 13:30:32 GMT 2016

On the zedboard, I think that the bigger problem is that the ARM CPU is
using all the hard-wired peripherals, so you basically have to shut it off
from the outside world to give the peripherals to the RISC-V.

Of course, when I say that, I'm talking about the SDIO controller and
ethernet. We generally do not use the UART or USB OTG controller from the
ARM processors. So I think it's easy to hand those off to the RISC-V to
give yourself a full untethered system, as long as the RISC-V has an AXI
master port for doing DMA.

Maybe adding a PMOD SD for filesystem. PMOD E is connected to the second
SDIO controller, but the pinout of the connector does not match the pinout
of the Digilent PMOD SD module, so you'll need to use some fly wires to
swizzle the pins to the right place, and then you'll need to reduce the
maximum speed of the controller because fly wires are not good for high
speed signals. I think we reduced the max to 15 or 25 MHz.

On the ZC706, the second ethernet MAC is connected to the SFP+ cage, so
it's available for the RISC-V core.


On Mon, Jan 25, 2016 at 6:12 AM Wei Song <ws327 at cam.ac.uk> wrote:

> Hello Alexis,
> Untethered SoC on Zedboard is not in current plan unless someone would
> like to help.
> The problem for Zedboard is that nearly all IO devices are on the ARM
> side where the programmable logic side has no direct control.
> In theory it is possible to configure the ARM side and give IO access to
> the programmable logic but it is complicated in practice.
> As a result, we decide to go straight to pure FPGA boards such as KC705
> and Nexys4-DDR.
> I see your question on the RISC-V maillist.
> Basically you have two options if you must use the ZedBoard:
> 1. Find out a way to give the programmable logic side direct access to
> IO devices. There are some examples online about letting microblaze
> coexist with ARM.
> 2. Use some Pmod breaking boards to give the programmable logic side
> extra UART or even SD.
> Best regards,
> Wei
> On 25/01/2016 11:01, Alexis Ramos Amo wrote:
> > Hi,
> >
> > I've seen that new Untethered lowRISC 0.2 lacks of support for Zynq
> Zedboard.
> > Are you going to add support for this board or any of the Zynq family
> (like ZC706) in the future?.
> >
> > Thank you
> >
> >
> > Alexis Ramos Amo
> > Researcher
> >

More information about the lowrisc-dev mailing list