[Oberon] Oberon on Nexys DDR4 from Digilent?

Skulski, Wojciech skulski at pas.rochester.edu
Thu Feb 22 21:07:26 CET 2018


  I was thinking of donating the Arty-7 and also our future RiskFive. However, at this point we are still not sure concerning the DDR3 firmware memory controller for Arty-7. If it works with Arty-7, the DDR3 controller will also work with RiskFive. Achieving success with Arty-7 is therefore a key to RiskFive production.

I am myself quite surprised that the DDR3 memory controller could be a problem. Artix-7 has a built-in DDR3 circuitry. So I thought it would work. However, there are mixed reports concerning its performance. I have seen claims that memory access takes about 25 clock cycles, which means 62.5 ns at 400 MHz. It would be slower than the SRAM access (25 ns). Quite surprising for a part running at 2.5 ns clock. On the other hand, the OpenArty design is claimed to run at 81.25 MHz on the Arty-7 with speed grade 1, see opencores.org/project,openarty

I am not sure what OpenArty is really doing. We keep investigating.

If we can make Arty-7 work then it would be an attractive development platform for a fairly unrestricted Oberon System. It is inexpensive and it can be equipped with PS2, SD, and 12-bit VGA. This vision keeps us working on Arty-7.

Nexys 4 DDR could be another good option, though I am not sure how the DDR2 can be faster than DDR3, using the same MIG memory interface. 

On the other hand, in case Chris wants to only use the internal BRAM without touching the external memory, then neither board is a viable path towards the full Oberon System.

From: Oberon [oberon-bounces at lists.inf.ethz.ch] on behalf of Pablo Cayuela [pablo.cayuela at gmail.com]
Sent: Thursday, February 22, 2018 2:31 PM
To: chris at cfbsoftware.com; ETH Oberon and related systems
Subject: Re: [Oberon] Oberon on Nexys DDR4 from Digilent?

I would put my real cents to donate the board to Chris Burrows.
What do you think fellows?

I could also help him to port Oberon to Nexys 4 DDR with our students help.
We have one previous version with Artix7 but without DDR at our university laboratory.

Prof. Pablo Cayuela

El feb. 21, 2018 4:38, "Chris Burrows" <chris at cfbsoftware.com<mailto:chris at cfbsoftware.com>> escribió:
> -----Original Message-----
> From: Oberon [mailto:oberon-bounces at lists.inf.ethz.ch<mailto:oberon-bounces at lists.inf.ethz.ch>] On Behalf Of
> Paul Reed
> Sent: Tuesday, 20 February 2018 4:14 AM
> To: ETH Oberon and related systems
> Subject: Re: [Oberon] Oberon on Nexys DDR4 from Digilent?
> > I'd like to use Oberon on this board.
> Can you tell us more about your intended application?  If you can get
> by with a quarter of the RAM (using the 35T's internal block RAM; or
> half, if the 100T version becomes available again) you may be able to
> use CFB Software's Astrobe for RISC5 and Embedded Project Oberon:
> http://www.astrobe.com/RISC5/<https://urldefense.proofpoint.com/v2/url?u=http-3A__www.astrobe.com_RISC5_&d=DwMFaQ&c=kbmfwr1Yojg42sGEpaQh5ofMHBeTl9EI2eaqQZhHbOU&r=uUiA_zLpwaGJIlq-_BM9w1wVOuyqPwHi3XzJRa-ybV0&m=AQ35DuwSckX2zJOsIEsVZzlWwIdzeqlOl9j2Iyj4BRE&s=T1NpeZAA2-x-F6FbPeijvHnsJVCyVtVNByAbj_FKM2o&e=>
> Chris, what do you think?

I wouldn't expect any problems as Embedded Project Oberon already runs well
on Xilinx's Artix-7 35T on Digilent's Arty A7 and Cmod A7-35T boards. If
anybody wants us to support it on the Nexys DDR4 from Digilent all they
would need to do is supply us with a board to run it on. We would return the
board to them if unsuccessful.

Chris Burrows

CFB Software

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