Artix development boards

[concept]

Hello, I'm looking for the fastest Artix development board that you have (in terms of DDR3 transfer rate).  

The Artix A7 says that it runs at 667MHz (so I assume that means 1333MT/s)

The Nexys Video Artix board says it runs at 400MHz (800MT/s).

Why is the Artix A7 so much faster than the Nexys video Artix board? or am I missing something?

Both designs seem to use the Artix (-1) speed grade.

thanks

Edited June 22, 2023 by concept
more info

[artvvb]

Arty A7's DDR runs at up to 333.33 MHz (~667 MT/s). We'll get it fixed on the site.

Thanks,

Arthur

[zygot]

23 hours ago, concept said:

Why is the Artix A7 so much faster than the Nexys video Artix board? or am I missing something?

Both designs seem to use the Artix (-1) speed grade.

Well, you had a good question. The answer, "our advertising was a misstatement and we haven't gotten around to fixing this for any of the boards, except the Nexys Video, which we just did this week.." isn't much of an answer. You deserve better.

The Arty A7-100T uses a XC7A100T-1CSG324C FPGA and 1 MT41K128M16JT-125K DDR3 memory according to the latest schematic.

The Nexys Video uses a XC7A200T-1SBG464C FPGA and 1 MT41K256M16HA-187E DDR3 memory according to the schematic that I use.

Both FPGA devices are the same speed grade. Both DDR designs have a 16-bit data bus.

The Arty will be advertised as working at a 333.3 MHz PHY clock rate, once the fix to one web page is fixed.

The Nexys Video is advertised as working at a 400 MHz PHY clock rate ( was 800 MHz )

Since DDR3 clocks data on every PHY clock edge the MT/s is 2X the PHY clock rate.

The DDR memory on the Arty is a faster speed grade than the memory on the Nexys Video which is advertised as working at a higher PHY clock rate. 

Digilent wants the customer to figure out all of this for themselves.

Evidently, there's more to the story than MHz or MT/s as far as DDR performance is concerned. Anyone at Digilent willing to provide a better explanation as to what's going on here (aside from the aforementioned MHz gaff ?

Edited June 23, 2023 by zygot

[concept]

Hi zygot,

A few more questions

1- The arty A7 has proper termination on the ddr3 lines, where as the Nexys doesn't..  I would assume that the signal eye would be better on the Arty if the correct lengths were used, so would it be possible to run faster than 333MHz?  Also did your engineers try to run it faster and determined the max speed is 333MHz for reliable transfers?

2- has anyone tried to run the ddr3 at max speed (533MHz) for the artix (-1) on any of your boards?

thanks again

[zygot]

Good questions, and someone who works for Digilent should be giving you a reasonable answer since they designed the original board and later revisions, or had the board designed for them. I can only speculate as to what their goals were. It's entirely possible that the faster memory part just happened to be the cheapest one or only one available when the parts for the last board production run was ordered.